New trends in physics teaching, v.4; The ... - unesdoc - Unesco

I 

New trends 

in physics 

teaching 

Volume IV 

Edited by 

E. J. Wenham, NI. B. E. 

Fellow and Former Head 

of the Science Department 

Worcester College of 

Higher Education 

(United Kingdom) 

Unesco

The teaching of basic sciences

New trends in biology teaching 

Vol. I: 1967 (out of print) 

Vol. 11: 1969 

Vol. 111: 1971 (out of print) 

Vol.IV: 1977 

New trends in chemistry teaching 


Vol. I1 : 1969 (out of print) 

Vol. 111: 1972 

Vol.IV: 1975 

Vo1.V: 1981 

trends in home economics edslcation 

itks. 1966 (out of print) 

n education (in preparation) 

New trends in mathematics teaching 


Vol. 11: 1970 (out of print) 

Vol. 111: 1972 (second impression 1977) 

Vol. IV: 1979 

New trends in physics teaching 


Vol. 11: 1972 

Vol. 111: 1976 

Vol.IV: 1984 

Mathematics applied io physics. 1966 (out of print) 

New trends in integrated science teaching 




Vol.IV: 1977 

Vo1.V: 1979 

New trends in primary school science education. 1983 

Other Unesco Publication in School Science and Technology Education 

Mew trends in the utilization of educational technology for science education. 1974 

Mew Unesco source book for science teaching. 1973 (third impression 1979) 

Unesco handbook for science teachers. 1980 

Studies in mathematics education 

Vol. I: 1980 

Vol. 11: 1981 

Vol. 111: 1984 

Vol. IV: In preparation 

Teaching school mathematics. 1971 

Teaching school physics. 1972 

Teacher’s study guide on the biology of human population: Asia. 1975 

Teaching school chemistry. 1984 

Mew trends in school science equipment. 1983 

Unesco handbook for biology teachers in Africa (in press) 

Unesco handbook for biology teachers in Asia (in press) 

Science and technology education and national development (in preparation)

The opinions expressed in this publication 

are the responsibility of the authors and 

of the editor, and do not necessarily 

reflect those of Uneseo. Furthermore, the 

designations employed and the presentation 

of the material in this work do not imply 

the expression of any opinion whatsoever on 

the part of Unesco concerning the legal 

status of any country or territory, or of 

its authorities, or concerning the delimitations 

of the frontiers of any country or 

territory. 

Published in 1984 by the United Nations 

Educational, Scientific and Cultural Organization 

7 Place de Fontenoy 

75700 Paris 

Printed by Imprimerie de la Manutention, Mayenne 

ISBN 92-3-102165-6 

OUnesco 1984 

Printed in France

Preface 

The worldwide exchange of ideas and information plays an important role in Unesco’s programme 

to promote innovations for the improvement of science education at all levels. One of Unesco’s 

contributions to this international exchange is the publication of the series The Teaching of 

Basic Sciences. Volumes on New Trends have been published in this series, devoted to the teaching 

of such subjects as mathematics, physics, chemistry, biology and integrated science. The 

present publication is the fourth of New Trends in Physics Teaching. * 

In view of both the increasing public interest in matters related to energy and the persistence 

of some confusions in this area, it was decided to devote part of New Trends in Physics Teaching, 

VoZ. IV, to helping physics teachers to deal with some of the irreversible phenomena associated 

with the transfer, conversion and utilization of enerby. About half of this book thus deals with 

the concepts of energy, entropy and irreversibility, discussing recent efforts to teach them more 

effectively in a variety of countries. 

The other half of the book deals with new approaches to teaching optics, to experiments in 

and out of the laboratory and to training physics teachers; the concluding papers present recent 

ideas on science, technology and society which should be of interest to physics teachers. 

This volume is addressed to all those who are activhly interested in the improvement of physics 

education at any level, with the emphasis on secondary and early university: teachers in teachertraining 

institutions, members of examination boards, curriculum planners and other specialized 

personnel at ministries of education, secondary schopl teachers, school inspectors, students preparing 

to become physics teachers, etc. Certain chapters might also be used as background 

material at national or regional seminars devoted to the specific aspects of physics education 

discussed in this book, at which the related problems would be discussed within the local contexts. 

Like the preceding volumes in this series, Volume IV has been prepared with the active cooperation 

of the International Commission on Physics Education, in particular Professor A. P. 

French, past Chairman of the Commission, and Professor R. Sexl, its current Chairman. A special 

expression of gratitude is due to Professor E. J. Wenham who accepted the responsibility of being 

the Editor of this volume; the competence, care and devotion with which he has carried out his 

work will no doubt be appreciated as much by the readers as it has been by Unesco. 

The opinions expressed in this volume are those of the editor and the individual contributors 

and not necessarily those of Unesco.

Editor's Note 

The previous volume in this series of books on world-wide trends in physics education was based 

on the proceedings of an international conference. On this occasion, it was felt right to make the 

attempt to identify a small number of important trends and then to invite men and women 

known to be active in developing those trends to write about their experi es. With the active 

help and encouragement of the International Commission on Physics Ed on and Unesco, it 

was agreed that the dominant trend was towards a reconsideration of teaching about energy in 

secondary school and that this was linked with the introduction of new courses in which the 

links between science, technology and society were explored. 

But there were others. At international conferences on physics education at Oxford in 1978 

and at Trieste in 1980 it became clear that there was a re-birth of interest in the teaching of 

optics - largely as a result of the great interest which was being shown by industry, commerce 

and the universities in the formation of images. 

At this time, it proved quite impossible to ignore the very great interest in the application of 

the microprocessor to the physics laboratory. Perhaps a whole volume should have been devoted 

to this, but it was felt that the time was not ripe for such an ambitious venture. 

Two continuing themes in any volume on trends are the education of physics teachers and the 

design of new and simple experiments for the children to do. 

A great debt is owed to the authors of the papers which together make 

most fortunate in having been allowed the privilege of working with them. 

respond willingly, constructively and promptly to my inquiries; I am indeed g 

My indebtedness to the staff of Unesco and to the members of the International Commis * 

on Physics Education for their help, advice and encouragement must also be expressed. And 

finally I wish to record my special thanks to the then Chairman of the Commission, Professor 

A. P. French, to its Secretary, Dr. P. Kennedy, and to Rosemary Dupuy, my secretary, and Mary 

Owers, the artist, for their help, their advice and their encouragement. 

E. J. Wenham, M.B.E., 

Fellow and Former Head of the Science Department, 

Worcester College of Higher Education, 

Worcester, 

United Kingdom.

Contents 

Part I 

Energy: the Background and the Way Ahead 

Introduction .. .. .... .. ...... 

Energy: facts and figures 

T.D.R. Hickson .. .... .. .. .... 

Forgotten fundamentals of the energy crisis 

A.A. Bartlett .. .... .. .. .. . . . . 

Measures of energy and power in terms of solar input 

A.P. French .... .. 

.. .. .. .. 

Entropy and information 

R.U. Sex1 and A. Pflug .. .. .. .. .. .... 

Energy and energy degradation as complementary aspects of energy 

processes and a stepwise introduction to the concept of energy 

H. Schlichting .. .. .... .. . . . . . . . . 

.. 

.. 

.. 

.. 

.. 

.. .. 

.. .. 

.. .. 

.. .. 

.. .. 

.. 

3 

6 

20 

38 

40 

58 

Part 11 

Energy Teaching in Secondary Schools 

Introduction .. .. .. .... .... . . . . 

The teaching of energy in Japan 

K. Hirata .. . . . . .. .. .. . . . . .. .... 

The teaching of energy in India 

B. Sharan .. .... .. .. .. .. .. .... 

The teaching of energy in Qatar 

N.H.A. Galil .. . . . . .. . . . . . . . . . . . . 

The problem of energy in the physics course in Soviet modern 

secondary schools 

G.A. Mesyats and Y.B. Yankelevitch .. .. .. .... 

Teaching energy in Hungarian schools: developing the concept 

over seven years 

F.J. Kedves, L. KOVBCS, and P. Kovesdi .. .... .. .. 

An experience in the teaching of energy in Italy 

A. Bastai Prat .. .... .... .... .... 

Reflection on current trends in physics teaching in upper secondary 

education and the first years of university education in Senegal: 

the teaching of the concepts of energy, entropy and irreversibility 

D. Fall .. .. .... .. .. . . . . 

.. 

.. 

.. 

.. 

.. 

.. 

.. 

.. 

.. .. 

.. .. 

.. .. 

.. 

.. 

.. .. 

.. 

73 

75 

89 

96 

104 

106 

116 

129

The planning and developing of an instructional system based on 

the classroom 'use of textbooks, with reference to energy, entropy 

and irreversibility 

C.Z. Dib, H.U. Gama and S. Magrini . . . . . . . . . . . . . . .. 

Energy education in the United States 

J.M. Fowler . . . . . . . . . . . . . . . . . . . . .... 

Introductory statistical physics 

J. Ogbom . . . . . . . . . . 

. . . . . . . . . . . . . . . . 

Part 111 

The Place of Optics in Physics Teaching 

Children's ideas about light 

E. GUCSIlt:.. . . . . . . . . . . .. . . . . . . ., .. .. 

Colour 

R.D. Edge .... .... .... . . . . . . . . .... .. 

Optics regained 

Taylor .. . . . . . . .... .... .... .... .. 

C.A. 

Part IV 

Teacher Education 

A case study of science teacher education for a new educational system 

J.M. Yakubu .. . . . . . . . . . . . . . . . . . . 

How to overcome the dilemma of physics education 

D. Nachtigall .. . . . . . . . . . . . . . . 

A curriculum development/teacher training scheme based on the 

study of solar energy 

P.E. Richmond . . . . . . . . . . . . . . . . . . . . . . 

.... .. 

.... .... .. 

Part V 

From Micro-computers to Low-cost Equipment 

Micro-computers as laboratory instruments 

J.W. Layman . . . . . . . . . . . . . . . . .... .... .. 

How to construct a solar cooker 

Physics Workgroup of the Science Education Center of the 

University of the Philippines . . . . . . .. . . . . . . .... .. 

String and sticky-tape experiments 

R.D. Edge . . . . . . . . . . . . . . . . . . . . .... .. 

Part VI 

Science, Technology and Society 

Introduction .. . . . . . . . . . . . . . . . . .... 

The teaching of science in relation to society 

J.L. Lewis .. .... .... .. .. 

Physics in society 

H. Eijkelhof and J. Swager . . . . . . .. . . . . . . 

Appropriate Technology 

M.K. McPhun . . . . . . .. . . . . . . . . . . . . 

Contributors .. . . . . . . .. . . . . . . . . . . . . 

.. 

.... .. 

. . . . .... .. 

.... .. 

.... .. 

.... .. 

133 

144 

157 

179 

193 

227 

253 

268 

280 

297 

30 1 

309 

343 

344 

35 1 

360 

367

Part I 

Energy: the Background and the Way 

Ahead

Introduction 

This section is concerned with one of the most important challenges to face the teacher of 

physics - that presented by the ‘Energy Problem’. To the teacher this problem has two aspects: 

the first is global, concerned with supply and demand, with resource and reserve, with ‘have’ 

and ‘have not’; the second is internal to physics education and concerned with relevant teaching 

and learning. 

Physics teachers can no longer hope to restrict their attention to the purely teaching problem 

and the traditional logical approach to it. That way required us to start with a force (which 

children found relatively easy to understand because they could feel forces), and then to define 

a parameter strangely called ‘work’ and finally to introduce energy through some such definition 

as ‘the ability to do work’. To many young minds, this traditional approach is so remote from the 

world in which they live that they decide that the whole business (and physics too) is quite 

irrelevant. 

Regrettably these young people are right in perceiving that a study of energy based solely on 

such a formalized approach makes very little contribution to their understanding of the world’s 

energy problem. It may even be a hindrance to the man or woman in the street who tries to 

understand what he or she reads about energy in the press. 

For example, one observes that the word ‘conservation’- which is now so very fashionable - 

means something quite different to the politician from what it means to the careful user of 

English in general and to the scientist in particular. To the politician and, as a result of intensive 

propaganda, to the man-in-the-street, the ‘conservation of energy’ has come to mean nothing 

more than the ‘saving of energy’. Advertisers wil say that if I eliminate some of the energy losses 

in my home or my factory, I shall ‘conserve’ energy. They mean that I shall ‘save energy’. To 

others the word conservation implies ‘preservation’; we may wish to assist in ‘the conservation of 

the countryside’ or ‘the conservation of an endangered species’. That is a legitimate use of the 

word. To the scientist, the word conjures up the image of the great conservation laws, the thought 

that energy is neither created nor destroyed as it is transformed from one form to another. If we 

are familiar with its limitations, that is a very useful statement. If we are not so familiar it may 

even appear to suggest that the ‘problem’ does not exist! Our students deserve to be alerted to 

such a difference in meaning. 

3

New Trends in Physics Teaching IV 

We, the teachers of physics, must help our students to understand - we must put them into a 

position in which they can interpret what they read or what they are told about energy in the 

press, by the oil companies, by the trade unions (to see coal miners leading an anti-nuclear lobby 

is surely worthy of sceptical comment) and all the other pressure groups. 

As teachers, we must have access to reliable information about energy in the global context, 

and about the effect of that knowledge on the approaches we might adopt in our teaching. That 

is the purpose of this first half of the part on Energy. However, the part is largely concerned with 

the impersonal and a few comments on the energy needs of human beings might be welcome. 

The energy unit which is most familiar to the men and women in the street is the kilowatt-hour 

of the electricity bill. Although it is, of course, 3600 kilojoules, its very familiarity makes it an 

attractive unit when one wishes to relate energy to a human context. 

An average requirement of energy for a human being is around 10 000 kJ per day. That is just 

under 3 kWh. And the rate of supply is just over 0.1 kW. 

If I switch a 100 W electric lamp on for 24 hours, that lamp converts energy at a rate of 0.1 

kW; and, in 24 hours, wil use 8640 kJ or 2.4 kWh. 

So you and I live by converting energy at about the same rate that a 100 W lamp converts 

energy. 

We derive this energy for living from our food. Any biology text will supply details of the 

energy which is available to us from various foodstuffs. However, those textbooks usually omit 

to point out that the foods themselves require energy for their production and that this too has 

to be paid for. Consider a loaf of bread - a staple item in so many lands. According to P. Chapman 

[ 11 a typical loaf of about 1.4 kg provides its consumer with about 14 000 kJ or nearly 4 kWh. 

To make that loaf from the wheat (allowing for the farmer’s, the miller’s, the baker’s and the 

shopkeeper’s usage of energy) requires 20000 kJ (5.5 kWh). 

The field of wheat from which the bread was derived may be thought of as a solar farm consuming 

solar energy and storing it up in the grain. We human beings then extract about 3.5 kWh 

(12 500 kJ) from each kilogram of the harvested crop. If we were to burn the crop we should 

get three times as much. But not in so useful a form. The energy would have been degraded. 

The energy we extract from the loaf of bread has, through the process of photosynthesis, 

been derived from solar radiation. Measurements from space craft confirm that the Earth receives 

energy from the Sun at a rate of about 1.4 kW per square metre. Taking the Earth’s diametric 

plane as of area 1.23 X lOI4 m2, the total input of energy to the Earth is 17.2 X 1OI6 W. Since, 

over a long period of years the mean temperature of the Earth has remained very close to its 

present value (280 K), we must conclude that just as much energy is radiated back into space as 

is received. Figure 1 gives details of the intervening energy flows. 

Of course, Stefan’s Law describes the process of radiating the energy back into space. 

and 

Dividing Eq. 2 by Eq. 1 

E = kT4 Eq. 1 

AE = k4T3AT Eq. 2 

AA E = 4r AT 

or Eq. 3 

4

~ and 

Introduction 

This simple relationship implies that if the energy to be radiated is increased by 1 per cent the 

temperature of the radiator must increase by 0.25 per cent. 

As we have seen, the energy input from the Sun is about 172 X lo1' W. Currently, the energy 

input from the various activities of human beings as they convert stored energy for their own 

purposes is around 5 X lo1' W (0.003 per cent of the input). It appears that we need not be too 

concerned about this. But, if our use of such fuels were to increase at the present rate of about 

4.3 per cent per year (corresponding to a doubling time of 16 years), the waste heat input would 

reach about 1 per cent of the solar input in about 140 years. The equation shows that this would 

have produced a temperature rise of about 0.75 K. The effect on the world's climate - particularly 

on the size of the polar ice-caps and hence on the depth of the sea - is not known! It could 

well be disastrous for those who live in the low-lying areas of the world. 

Solar radiation 

17 2 3'"w 

Reflected 

sun1 i g ht 

5 2 x 1o'"w 

Lonq wave radiation 

A 


Energy: facts and figures 

T. D. R. HICKSON 

In this brief survey of the energy situation in the world today, an attempt has been made to draw 

together information from a wide variety of sources so as to produce data with which most people 

wil agree. To expect total reliability is to dream. No matter how reliable a source may appear to 

be, sooner or later it is likely to be found to conflict with another authority. All that can be 

hoped for is to make comparisons and to discern trends. 

Quantities of energy have been quoted in kilograms of coal equivalent (kgce) or millions of 

tonnes of coal equivalent (Mtce). This seems to be most appropriate as the world enters a second 

era of growing importance for coal. 

Human progress has always been closely associated with the availability of energy. Indeed an 

early energy crisis occurred in the late sixteenth century. Holland and England were both affected 

by an acute shortage of fuel wood. As a consequence of a general rise in mercantile prosperity, 

more and more timber was needed for ships, for houses, for iron-smelting, for firewood, for 

salt-making, soap-boiling, brewing and for domestic uses. Although timber could be imported, 

the solution which lay most readily to hand was coal. Thus was born the first Industrial Revolution 

and, with it, an acceleration in the rate of growth of energy use. 

Although natural gas has been used on a small scale for a very long time, it was the introduction 

at the end of the eighteenth century of synthetic gas, produced from coal, for lighting that really 

began the exploitation of this fuel. In the middle of the present century, large deposits of natural 

gas were found. Once the problems of transport over large distances were solved, natural gas 

became an important source of energy. 

Finally, the discovery of oil in the late nineteenth century coupled with the development of 

the internal combustion engine - and its use in road transport - completed the trio of fossil 

fuels upon which twentieth century industrial development has depended. 

WORLD ENERGY DEMAND AND SUPPLY 

When considering the way in which the nations of the world consume energy, two points are 

obvious. The first is that, in spite of political and economic upheavals, the rate of consumption 

6

Energy facts 

is increasing; the second is that the distribution of energy amongst the peoples of the wortd is 

grossly uneven. This second fact is usuaIly illustrated by showing the correlation, rou 

it is, between energy consumption and Gross National Product (GNP) per capita. Figure la, b 

shows the approximate situation during the past decade. 

12 ono 

(U 

U 

;,0000 

---. 

0 

Q 

0 @OD0 

0 

h 

Y 

5 

60c10 

C 4000 

U 

z 

P 

; 2000 

U1 

0 

-United States 

Canada 

. Czechoslovakia 

German 

=morratiC Republic * 

Australia 

Netherlands . 

Federal Republic * Sweder 

of Germany 

US S R .United 

Kingdom 

France 

Italy. 

Israel 

APgentina 

.Japan 

L byan Arab Jarnchiriya 

.Mexico 

p'na. Brazil 

lnda , I I , I I 

2000 4000 6000 SO00 13000 12000 

. Kuwart 

Figure 1. Energy consumption andgrossnational product. The figures are from the World Bank and refer to 1977 (kgce= kilogram 

of coal equivalent). 

400 t 

200 

Philippines 

Egypt 

.Zambia 

. Papua New Guinea 

India 

Pakistan 

*Ghana 

0 

Bangladesh 

Nigeria 

200 400 600 800 lo00 1200 

GNP per capita 

Figure lb is an enlargement of the bottom left hand corner of figure la. 

7


Alternatively, quoting from the Brandt Report [7] : ‘one (North) American uses as much 

commercial energy as 2 Germans or Australians, 3 Swiss or Japanese, 6 Yugoslavs, 9 Mexicans or 

Cubans, 16 Chinese, 19 Malaysians, 53 Indians or Indonesians, 109 Sri Lankans, 438 Malians, or 

1072 Nepalese. All the fuel used by the Third World for all purposes is only slightly more than 

the amount of gasoline the North burns to move its automobiles.’ 

When reporting the latest figures for energy consumption, most sources also include their 

predictions for future demand. These projections follow from estimates made of the rates of 

growth of GNP, usually of groups of nations. One such grouping is as follows: the industrially 

developed countries - Organisation for Economic Co-operation and Development (OECD) plus 

Israel and South Africa; the so-called ‘planned economies’ of the Union of Soviet Socialist 

Republics (USSR), Eastern Europe and China; the oil-exporting countries and the developing 

countries. These last are conveniently sub-divided into two groups: the high-growth group, consisting 

of Argentina, Brazil, Chile, Colombia, Hong Kong, Singapore, the Republic of Korea, 

Taiwan and Uruguay and the low-growth group made of the remaining countries. 

As 1973 approached, both the oil-exporters and the high-growth developing countries showed 

a growth in their GNP of almost 8 per cent per year and the industrial countries of nearly 5 per 

cent. The GNP of the low-growth developing countries climbed at over 4 per cent per annum 

whilst that of the planned economies rose at about 5% per cent. These growth rates are expected 

to slow considerably during the rest of the century. As a result, the optimists, usually including 

the major oil companies, expect the growth rate to fall to about 3 per cent whilst the more 

pessimistic refer to about 1% per cent. 

When basing predictions of future energy demand on these figures, note must be taken of the 

efficiency with which energy is used. The industrial countries, in particular, have improved, and 

are expected to continue to improve, the energy consumption per unit of GNP. This has largely 

come about as a result of industry installing more energy-efficient plant and so making better 

use of fuel. Moves in the United States to introduce smaller and more efficient motor cars may 

help to reduce its embarrassment at having some 6 per cent of the world’s population yet using 

about one third of the world’s annual energy production. 

Whereas before 1973, the annual percentage rate of growth had tended to increase, since that 

date the trend seems to have reversed. This is reflected in the five-year averages shown in figure 2. 

The general consensus amongst the sources consulted is that growth rate wil settle at about 

3 per cent and that even at this rate the world energy demand wil be 60 to 70 per cent greater 

than at present by the year 2000. 

However, it is obvious that attempting to satisfy this increasing demand for energy in general 

is not the only problem to be faced during the next two decades. For some years now, the world 

has been consuming more oil than it has been finding and now production is expected to peak 

around the end of this century. This must lead to higher fuel prices and to a need to move away 

from today’s heavy dependence on oil. 

Industrialized countries wil have to make even greater efforts to control their demand (see 

figure 3); they wil have to reach decisions about nuclear power and the need for new coal mines; 

and they must develop synthetic fluid fuels. The developing countries which import oil wil have 

to explore and develop their own sources of commercial energy at the same time as they increase 

the efficiency of non-commercial sources. The oil exporting countries wil be concerned to 

control the rate at which they deplete their resource whilst ensuring that their customers remain 

economically healthy. For such countries there are special difficulties in making the transition 

to a future with little or no oil. 

8

Energy facts 

396,R 

0 

0 

0 

0 

0 

, 

L 

x 

; 10 

0 

0 

2 

0 

- 

Percentage annual growth rates 

- 

-4 6-6-3 5-3 3+ 

- 

I I I I 

Figure 2. World energy demand. 

r 0.3% 

Shares of World 

P oDulat ion 


Energy Production 


Energy Consumption 

Developing 

Countries 

Centrally Planned 

Economies 

Industrialised 

Countries 

Capital Surplus 

Oil Exporters 

Figure 3. Population, energy production and consumption. Based on World Bank statistics for 1976, the figure shows how the 

industrialized countries, accounting for more than one third of world production and more than one half of world consumption, 

dominate the energy market. 

9

I 


20 000 

, 

0 

.- 

L x 

‘IO 000 

(U 

0 

5 

-__--- --- 

Synthetics and VHO 

01 

0 I I I I 

1960 1970 1980 IS90 2000 

Figure 4. A projection showing how the energy demands may be met up to the year 2000. 

The graph (figure 4) includes a typical projection up to the year 2000 showing how the major 

.oil corporations tend to expect the demand to be supplied by various sources. 

Coal production is expected to increase, partly to replace oil and gas in the production of 

electricity and partly to satisfy new demands for space and process heating. If it is also used to 

produce synthetic oil and gas it could well return to its former dominance over oil. Even so the 

ratio of world proven reserves of coal to the estimated production rate wil still be significantly 

greater than that for oil. (On present production rates, the ratio for coal is about 200 years 

whereas that for oil is 30 to 40 years.) 

Nuclear energy is expected to grow also. However, the increase in the use of both coal and 

nuclear energy wil be affected by concern for the protection of the environment, safety and 

cost relative to oil. At the present time these factors have caused long delays in nuclear power 

developments. Furthermore, incidents such as that at Three Mile Island in the United States 

have heightened public sensitivity to safety hazards. Coal, too, is costly to transport and not as 

convenient as oil or gas to handle. 

The growth in hydro-power is expected to occur mainly in South America but also in Canada 

and the USSR. Geothermal and solar energy are the principal components of the ‘other’ sources. 

Ocean thermal electricity, wind, wave and tidal power are also included but their contribution 

is expected to be very small. 

Synthetic fuels and heavy oils are expected to become a major source of supply growth. This 

wil occur mainly in the United States but also in Canada, Brazil, Venezuela and Australia. 

10

Energy facts 

0 il 

TABLE 1. Oil demand and supply in 1979 

Demand Mtce/yr Supply Mtce/yr 

United States 1500 United States and Canada 1000 

Europe 1250 Europe 150 

Japan 400 Organization of Petroleum 

Other industrial countries 350 Exporting Countries (OPEC) 2700 

Developing countries 900 Non-OPEC exporters 5 00 

Centrally planned economies 1100 Centrally planned economies 1200 

TOTAL 5500" 5550" 

"The discrepancy between these totals results from rounding off numbers which have been converted from 

those using other units. lhs is always a problem when trying to compare quantities which are given in many 

different units. If converted data are not rounded off, they appear to acquire a strange precision. For example, 

the proved recoverable reserves of hydrocarbons given at the 1980 World Energy Conference was quoted in the 

magazine Atom as 11 184 746.2 petajoules. The same quantity given by the major oil corporations is 6 900 000 

petajoules. 

In the major industrial countries demand for oil is expected to drop as a result of savings, 

efficiency improvements and substitution of alternative fuels (see Table 1). It is only in the 

field of transport that there is likely to be little substantial change in demand during the remainder 

of this century. 

The centrally planned economies (CPEs) are expected to increase their demand for oil but not 

by more than about 1 per cent annual1y:China expects a rapid growth of coal production, and 

in the USSR, natural gas production wil increase. As a result, CPEs are expected to remain 

marginal exporters of energy. 

Oil consumption in the developing countries is expected to grow considerably, mainly as a 

result of the oil-exporting countries pursuing industrialization policies designed to use a significant 

share of their energy resources. 

Gas 

In contrast to oil, the current gas discovery rate still exceeds the gas production rate and it is 

thought that this state of affairs could well continue to the end of this century. Indeed there are 

countries which still 'flare-off' gas released in the extraction of oil. The peak in gas production 

is not expected to be reached until well into the 21st century. As a result, the availability of 

reserves is not expected to be a limiting factor. The most important problem to be solved is the 

development of large-scale international gas transport systems. There are significant quantities of 

gas available in remote areas in Latin America, Africa and the Far East. 

11

~ 


TABLE 2. Gas demand and supply 1979 

Demand Mtce/yr Supply Mtce/yr 

United States 

Europe 

Other 

CPE 

TOTAL 

880 United States and Canada 

330 Europe 

330 Middle East and Africa 

660 Far East and Latin America 

CPE 

Synthetics 

2200 

950 

290 

110 

150 

680 

20 

2200 

Coal 

After a period in which the use of coal actually declined, world demand is expected to double 

during the remainder of this century. Its main use is likely to be for an increasing part in the 

production of electricity, for the production of industrial heat and for the production of liquid 

fuels. The greatest constraints on coal use will continue to arise from environmental limitations. 

TABLE 3. Coal supply in 1979 

Supply 

Mtce/yr 

United States 1300 

Europe 690 

Far East 400 

CPE 2970 

Other 340 

- 

TOTAL 5700 

All the suppliers quoted in Table 3 are able to increase their output. That of the United States 

is expected to show a substantial increase as is that of China. Grouped under ‘Other’ in Table 3 

and also expected to show increases are India, Brazil, the Republic of Korea, Turkey, Yugoslavia 

and the Socialist Republic of Viet Nam. Production for export markets wil also increase in 

Australia, South Africa and Colombia. 

TABLE 4. World oil,gas and coal reserves 

North America 

Caribbean and South America 

Western Europe 

Africa 

Middle East 

Far East and Australasia 

USSR, Eastern Europe and China 

TOTAL 

Mtce 

Crude oil Natural gas coal 

15 600 

6200 

3200 

13 100 

83 000 

4400 

18 400 

13 600 

4400 

4800 

7600 

25 800 

6400 

38 200 

207 000 

11 000 

101 000 

38 000 

200 

73 000 

271 000 

143 900 100 800 701 200

Energy facts 

1960 

1979 

Natural Gas 

n Nuclear 

.. 

El 

Hydro and other 

Coal 

Figure 5. Changes in the contributions of various sources to the world energy supply, 1960 to 1979, in lo8 tonnes of coal 

equivalent per year. 

Nuclear energy 

Since nuclear energy is used solely for the production of electricity, the demand for this convenient 

source of power necessarily regulates the rate of growth of nuclear energy sources. In 

recent years, estimates of the rate of growth of demand for electricity, particularly for the 

industrialized countries, have tended to moderate. This, together with the environmenta1 constraints, 

long lead-times and limited capability for using nuclear energy for ‘load-following’ has 

caused some utilities in the major capitalist countries to back away from plans for nuclear 

expansion. 

However, since it seems that nuclear energy wil remain the lowest-cost source of base-load 

electrical power, the economic incentive for nuclear power generation wil continue to be strong. 

For this reason, together with the need to replace the use of oil and gas in power stations, it is 

generally agreed that nuclear energy could be the fastest growing major energy source. Some 

common projections see its share of the world energy supply being 10 per cent by the year 2000 

and its share of electric power generation 30 per cent. 

As a result of the long periods of time between the decision to build a power station and its 

coming into operation (lead-time), we already know what the nuclear energy supply is likely to 

be in 1990. 

13


TABLE 5. World nuclear energy supply 

Mtce/yr 

1979 1990 

United States, Canada, Europe, Japan 213 679 

Centrally planned economies 25 220 

Other 7 57 

TOTAL 245 956 

- - 

Amongst the developing countries a few, including Argentina, China, India and Pakistan already 

have nuclear power while others, such as Brazil and Mexico, are expected to become producers 

soon. In developing countries, apart from the usual causes for concern over nuclear power, the 

demanding requirements of technical and managerial expertise and the need for plants to be large 

to be commercially viable, tend to limit their use to middle income and large countries. 

Synthetic fuels and very heavy oil 

It is generally agreed that synthetic fuels and very heavy oil wil be important factors in the energy 

supply picture for the next few decades. Synthetic fuels include oil from shale, liquids produced 

from coal or natural gas, gas produced from coal, alcohol and methanol. Very heavy oil (VHO) 

‘is the term used for oil whose primary production requires the use of heat or mining. At the 

present, the only large scale production is of alcohol in Brazil, very heavy oil in Canada and 

liquid fuel from coal in South Africa. 

There are optimistic forecasts that suggest that by 1990 synthetic fuels and very heavy oil will 

account for a significant share of oil and gas demand in Brazil, Canada and Venezuela. By 2000, 

they are expected to become important world-wide. An Exxon corporation projection (1 980) 

is shown in Table 6. 

TABLE 6. Synthetic fuels and VHO as a percentage of oil and gas demand 

1990 2000 

United States 

Canada 

Venezuela 

Brazil 

Australia 

Others 

World, excluding CPE 

5 18 

15 17 

30 55 

25 34 

3 

1 

28 

2 

4 9 

These forecasts are optimistic since they require governments to make decisions to embark on 

large-scale projects in the early 1980s. 

The United States is expected to lead in synthetic fuel development in the 199Os, because of 

its vast resources of coal and of oil shale, as well as its desperate need for alternatives to imported 

oil.A number of synthetic fuel projects are already at the advanced planning stage. 

Production from Canada’s Athabasca heavy oil or tar sands is expected to make that country 

the leading producer of very heavy oil by 1985. In Venezuela, the government has already 

14

Energy facts 

announced plans to develop the Orinoco heavy oil belt. Peru and Ecuador also have large deposits 

of heavy oil. 

Brazil, China and Zaire, for example, possess substantial shale oil reserves. Furthermore, Brazil 

is expected to continue to be the leader in alcohol production for motor fuel supplies. Alcohol 

from fermented sugar cane at present accounts for 20 per cent of Brazil’s gasoline consumption 

and it is planned to increase that to about 85 per cent in the 1990s. 

Australia also has large shale oil reserves which it is expected to develop. 

Renewable energy sources 

With the continued technological development, solar energy sources are expected to become 

major sources of supply in the 21st century. If the nuclear physicists are successful, this could 

eventually be joined by nuclear fusion. However, with the exception of hydropower, the contribution 

of renewables to total, commercial energy supplies is expected by most people to be 

relatively small for the rest of this century. 

Obviously, non-commercial renewable sources of energy wil have some effect on the demand 

for commercial energy if their use were to increase. As an example, in some parts of the world 

rooftop water tanks or other simple devices capture solar energy. If these became more widespread, 

there would be a slight reduction in the demand for, say, electrical energy. On the other 

hand, in many parts of the world, firewood and dung are used to provide energy for cooking and 

heating. If this fuel became unavailable, then there might be a substantial increase in the demand 

for commercial energy of some sort. 

Photovoltaic electricity, the direct conversion of sunlight to electricity, cannot compete at 

present with central power grids but it can be economical at remote installations where the 

alternative is batteries or small diesel-driven generators. Technology must reduce costs to a tenth 

or less of current levels before photovoltaic electricity becomes economically competitive on a 

larger scale. Even then, the land area required could be inhibiting. 

Few projections suggest that wave, wind and tidal power sources are capable of providing 

much more than 8 million tonnes of coal equivalent per year of electricity before the end of the 

century. 

THE DEVELOPING COUNTRIES’ ENERGY OUTLOOK 

Over the next few decades, the developing countries are expected to account for much of the 

growth in the world’s demand for energy and virtually all of the growth in the consumption of 

oil. Most projections suggest a growth in total energy demand of more than 5 per cent per annum 

through to the year 2000. 

The traditional sectors of developing economies rely heavily on energy from firewood, charcoal, 

plant and animal residues, human and animal effort, solar energy and, to a lesser extent, wind and 

water power. In the majority of developing countries today, these forms of energy supply about 

half the total energy demand whilst in rural areas, the proportion goes up to over 80 per cent. 

The demand for such fuels is dominated by household uses, primarily cooking. At present, about 

half the world’s population cooks with locally gathered fuel. 

Deforestation and fuelwood shortages are becoming a critical problem, just as they were in 

Europe in the late sixteenth century. In Nepal, the growing demand for fuelwood, fodder and 

cultivable land is denuding the hillsides and causing severe erosion. Haiti and El Salvador are 

meeting similar problems, which, in the Sudan, have contributed towards the growth of the 

15


desert. In many countries it appears that wood is being used for fuel at rates faster than their 

forests can sustain. Many more are experiencing severe fuelwood shortages around densely 

populated areas. 

In addition, as wood becomes more and more difficult to obtain there is a tendency to use 

animal and crop residues, with serious implications for agriculture. This seems to be particularly 

significant in the drier areas of Africa, much of South Asia and some parts of Latin America. 

To tackle this problem, some countries, including the Philippines and the Republic of Korea, 

have launched promising afforestation schemes on a large scale. With the use of appropriate fastgrowing 

trees it seems possible to make an area yield five times as much fuelwood as a natural 

forest. 

In China, Taiwan, India and the Republic of Korea, biogas plants are in use. However, economies 

of scale make them more viable for relatively wealthy families with four or five head of cattle 

and enough land to use the sludge produced for fertilizer. An Indian subsidy programme for 

biogas plants was discontinued when it was found to have increased the effective price of dung, 

causing hardship to the poor. 

Alcohol fermented from agricultural products can be used for cooking, but it is more costly 

than petroleum and production is still small scale, except in Brazil. 

Fuel for industry and for transport, however, must come mainly from oil, gas and coal. Of the 

oil-exporting countries, Nigeria and Indonesia also have significant reserves of coal. The countries 

with a high economic growth rate, Argentina, Brazil, Chile, Colombia, Hong Kong, Singapore, the 

Republic of Korea, Taiwan and Uruguay, are expected to have to import oil and sometimes coal 

during the next decade. The remaining developing countries are expected to depend mainly on 

domestically produced fuel with some imported oil. 

A LAST WORD 

It seems appropriate to let the Brandt Report [7] have the last word. 

Energy shortages take many forms. Sudden rises in petroleum prices affect all countries; but while pleasure 

motoring continues on a large scale, fishermen in poor island communities like the Maldives may not get oil at 

all to operate their boats, or farmers in India or Pakistan to work their irrigation pumps. The energy crisis in 

much of Africa and Asia means the shortage of firewood: poor families have to search further and further to 

find wood to cook their rice and wheat, while more of the land is denuded of trees. Many developing countries 

are experiencing balance of payment difficulties or economic stringency as higher expenditure on fuel forces cuts 

elsewhere. The long-term solutions lie in the development of alternative and renewable energy sources but the 

short-term difficulties are acute. Both require nothing less than a global strategy for energy. 

REFERENCES 

Information has been obtained from a wide variety of sources including the following: 

1. COOK, E. Man, Energy, Society. San Francisco, Calif., W.H. Freeman & Co., 1976. 

2. Energy and Power. Scientific American (New York), Vol. 225, No. 3, September 1971. 

3. Energy in Profile. London, Shell International Petroleum Co. Ltd., 1980. 

4. Energy Prospects to 1985. Paris, Organization for Economic Co-operation and Development (OECD), 1974. 

2 vol. 

16

Energy facts 

5. Energy Resources. Milton Keynes, Open University Press, 1976. 

6. KENWARD, M. Potential Energy. New York, Cambridge University Press, 1976. 

7. North-South: a Programme for Survival (The Brandt Report). Cambridge, Mass., MIT Press; London, Pan 

Books Ltd., 1980. [The Report of the Independent Commission on International Development Issues.] 

8. WORLD BANK. World Development Report. Oxford, Oxford University Press, 1980. 

9. World Energy Outlook. New York, Exxon Corporation, 1980. 

10. World Energy Conference, llth, Munich, 1980. Energy for Our World. London, World Energy Conference, 

1980. 

And many articles in such journals as Atom (London, United Kingdom Atomic Energy Authority), New 

Scientist (London, IPC Magazines Ltd.),Scientific American (New York, Scientific American Inc.). 

APPENDIX 1 

Units 

This paper has been consistent in its use of the kgce and Mtce to compare energy quantities. 

1 Mtce = lo9 kgce 

Many other units are in use however; some of these are listed below. 

The joule family 

The basic unit of energy is the joule (J). 

Multiple units are the kilojoule kJ lo3 J 

megajoule MJ = 106J 

gigajoule 

GJ lo9 J 

terajoule TJ 1012J 

petajoule PJ = loE J 

Units associated with the joule include:- 

The Q unit 

1 Q unit 

The kilowatt hour (kWh) = 3.6 X 106J 

= 1.06 X 1021 J = l0”J 

The megawatt hour (MWh) = 3.6 x 1 09~ 

The gigawatt hour (GWh) = 3.6 X 1012J 

Approximate equivalents of other units 

Each of the following is approximately equivalent to 1 tonne of coal (tce):- 

2.8 X 10’OJ 

8 X lo3 kWh 

0.588 tonnes of oil 

750 m3 of natural gas. 

1 tonne of oil equivalent (toe) is approximately equivalent to 1.7 tce or 4.76 X lolo J. 

1 GWh is approximately equivalent to 135 tce and 80 toe. 

1 barrel of oil is 0.13 tonnes (equivalent to 6 X 1 O9 J). 

17


APPENDIX 2 

A selection of other statistics 

1. The daily energy requirement of a human being depends on his or her mass and the work 

being done. Some average figures (all in kJ per day) for adults are:- 

Men 

Women 

Lying in bed 

Light work 

Heavy work 

7400 

11 600 

14 700 

6300 

9500 

12 500 

As a rough average one can take 10 000 kJ per day, which is a little more than the energy 

transformed by a 100 W lamp in 24 hours (8640 kJ). 

2. Power station efficiencies (about 30 per cent) 

Fuel - 1000 units 

850 units 

Flue Gases 

150 units 

Steam Turbine 

and Alternator 

I 

Cooling Water 

550 units 

Electrical Energy 

300 units 

Note that these efficiencies determine the efficiencies of energy conversions in the electrical 

appliances used in industry and in the home. 

3. A special problem in temperate and cold climates 

Heat losses from houses: through the roof 25 per cent 

through the windows 10 per cent 

through the walls 35 per cent 

through the floors 15 per cent 

through draughts 15 per cent 

4. Energy costs in manufacture 

A tin of beans 

A colour television set 

A small motor car 

11 OOOJ 

25 000 MJ 

80 000 MJ 

18

5. Energy in history 

Energy facts 

The ratio of the energy collected for human use to the energy expended in the collection of that 

energy has been estimated to be:- 

For hunter-gatherers 10to 1 

For slash and burn agriculture 20 to 1 

For early technology based on wind and water l00to 1 

For current technology 1000 to 1 

6. Solar farms (1980 prices) 

A forest yields energy at 

A field of wheat yields energy at 

A silicon solar cell yields energy at 

U.S. $0.01 per kWh 

U.S. $0.05 per kWh 

U.S. $0.05 to 1.00 per kWh 

19


Forgotten fundamentals of the energy crisis 

ALBERT A. BARTLETT 

“Facts do not cease to exist because they are ignored”. Aldous Huxley. 

What are the fundamentals of the energy crisis? Rather than travel into the sticky abyss of 

statistics it is better to rely on a few data and on the pristine simplicity of elementary mathematics. 

With these it is possible to gain a clear understanding of the origins, scope and implications 

of the energy crisis. 

BACKGROUND 

When a quantity such as the rate of consumption of a resource is growing by a fixed percentage 

per year, the growth is said to be exponential. The important property of the growth is that the 

time required for the growing quantity to increase its size by a fixed fraction is constant. For 

example, a growth of 5 per cent (a fixed fraction) per year (a constant time interval) is exponential. 

It follows that a constant time wil be required for the growing quantity to double its size 

(increase by 100 per cent). This time is called the doubling time T2, and it is related to P, the 

percentage growth per unit time, by a very simple relation that should be a central part of the 

educational repertoire of every person. 

As an example, a growth rate of 5 per cent/year wil result in the doubling of the size of the 

growing quantity in a time T2 = 70/5 = 14 years. In two doubling times (28 years) the growing 

quantity wil quadruple in size. In four doubling times it wil increase sixteenfold (24 = 16);and 

so on. It is natural then to talk of growth in terms of powers of two. 

THE POWER OF POWERS OF TWO 

Legend has it that the game of chess was invented by a mathematician who worked for an ancient 

20

The energy crisis 

king. As a reward for the invention the mathematician asked for the amount of wheat that would 

be determined by the following process: he asked the king to place 1 grain of wheat on the first 

square of the chess board, double this and put two grains on the second square, and continue in 

this way, putting on each square twice the number of grains that were on the preceding square. 

The filling of the chess board is shown in Table 1. We see that one wil place 2@ grains on the last 

square and that the total number of grains on the board wil then be one grain less than 264. 

TABLE 1. Filling the squares on the chess board. 

Square number Grains on square Total grains thus far 

1 

2 

3 

4 

5 

6 

7 

64 

1 

2 

4 

8 

16 

32 

64 

263 

1 

3 

7 

15 

31 

63 

127 

264 - 1 

How much wheat is 264 grains? Simple arithmetic shows that it is approximately 500 times the 

1976 annual world-wide harvest of wheat! This amount is probably larger than all the wheat that 

has been harvested by humans in the history of the earth! 

Exponential growth is characterised by doubling, and a few doublings can quickly lead to 

enormous numbers. 

The example of the chessboard (Table 1) shows us another important aspect of exponential 

growth; the increase in any doubling is approximately equal to the sum of all the preceding 

growth. When 8 grains are placed on the 4th square, the 8 is greater than the total of 7 grains that 

were already on the board. Covering any square requires one grain more than the total number of 

grains that are already on the board. 

On 18 April 1977 President Carter told the American people, ‘And in each of these decades 

(the 1950s and 1960s), more oil was consumed than in all of man’s previous history.’ 

We can now see that this astounding observation is a simple consequence of a growth rate 

whose doubling time is T, = 10 years (one decade). The growth which has this doubling time is 

P = 70/ 10 = 7 per cent/year. 

When we read (in 1975) [2] that the demand for electrical power in the United States was 

expected to continue its long-term history of 6 to 7 per cent growth per year and to double in 

the next ten to twelve years, we should recognize that this meant that the amount of electrical 

energy that was expected to be used in these ten to twelve years would be approximately equal 

to the total of all of the electrical energy that had been used in the entire history of the electrical 

industry in the United States. Many people find it hard to believe that when the rate of consumption 

is growing at a mere 7 per cent per year, the consumption in one decade exceeds the 

total of all of the previous consumption. 

Populations tend to grow exponentially. The world population in 1975 was estimated to be 

4 X lo9 people and it was growing at the rate of 1.9 per cent/year. It is easy to calculate that, 

at this low rate of growth, the world population would increase by I X 1 O9 in less than 12 years, 

the population would double in 36 years, the population would grow to a density of 1 person/m2 

21


on the dry land surface of the Earth (excluding Antarctica) in 550 years, and the mass of people 

would equal the mass of the Earth in a mere 1620 years! Tiny growth rates can yield incredible 

numbers in modest periods of time. Since it is obvious that people could never live at the density 

of 1 person/m2 over the land area of the Earth, it is obvious that the Earth wil experience zero 

population growth. The present birth rate and/or the present death rate wil change until they 

have the same numerical value, and this wil probably happen in a time much shorter than 550 

years. 

A report in 1976 suggested that the rate of growth of world population may have dropped 

from 1.9 to 1.64 per cent/year [3]. If this reported drop can be confirmed, the report would 

probably qualify as the best news the human race has ever had. The report seemed to suggest 

that the drop in this growth rate was evidence that the population crisis had passed, but it is easy 

to see that this is not the case. The arithmetic shows that an annual growth rate of 1-64 per cent/ 

year wil do anything that an annual rate of 1.9 per cent will do; it just takes a little longer. For 

example, the world population would increase by 1 X lo9 people in 13.6 years instead of 11.7 

years. 

Steady inflation causes prices to rise exponentially. An annual inflation rate of 6 per cent will, 

in 70 years, cause prices to increase by a factor of 64. If the inflation continues at this rate, the 

$1 .OO loaf of bread we feed children today wil cost $64.00 when those children are retired and 

living on their pensions! 

It is very useful to remember that steady exponential growth of n per cent/year for a period 

of 70 years (1 00 X ln2) will produce growth by an overall factor of 2n. 

The reader can suspect that the world’s most important arithmetic is the arithmetic of the 

exponential function. One can see that the world’s long history of population growth and of 

growth in per-capita consumption of resources lies at the heart of the energy problem. 

EXPONENTIAL GROWTH IN A FINITE ENVIRONMENT 

Bacteria grow by division so that 1 bacterium becomes 2, the 2 divide to give 4, the 4 divide to 

give 8 and so on. Consider a hypothetical strain of bacteria for which this division time is 1 

minute. The number of bacteria thus grows exponentially with a doubling time of 1 minute. 

One bacterium is put into an empty bottle at 11 a.m. and it is observed that the bottle is full 

at 12 noon. Here is a simple example of exponential growth in a finite environment. This is 

mathematically identical to the case of the exponentially growing consumption of our finite 

resources of fossil fuels. Keep this in mind as you ponder three questions about the bacteria: 

(1) When was the bottle half-full? Answer: 1 1.59 a.m.! 

(2) If you were an average bacterium in the bottle, at what time would you first realise that you 

were running out of space? Answer: There is no unique answer to this question, so let’s ask, 

‘At 11.55 a.m., when the bottle is only 3 per cent filled (1/32) and is 97 per cent open space 

would you perceive that there is a problem?’ See Table 2. 

22


TABLE 2. The last minutes in the bottle 

11.54 am. 

11.55 am. 

11.56 a.m. 

11.57 a.m. 

11.58 am. 

11.59 am. 

12 noon 

1/64 full (1.5%) 

1/32 full (3%) 

1/16 full (6%) 

1/8 full(12%) 

1/4 full(25%) 

1/2 full(50%) 

full (1 00%) 

63/64 empty 

3 1/32 empty 

151 16 empty 

718 empty 

314 empty 

1/2 empty 

no space left 

Suppose that at 11.58 a.m. some farsighted bacteria realized that they are running out of 

space and, consequently, with a great expenditure of effort and funds, they launch a search for 

new bottles. They look offshore on the continental shelf and in the Arctic and at 1 1.59 a.m. they 

discover three new empty bottles, Great sighs of relief come from all the worried bacteria, 

because this magnificent discovery is three times the number of bottles that had hitherto been 

known. The discovery quadruples the total space resource known to the bacteria. Surely this 

wil solve the problem so that the bacteria can be self-sufficient in space. The bacterial ‘Project 

Independence’ must now have achieved its goal. 

(3) How long can the bacterial growth continue if the total space resources are quadrupled? 

Answer: Two more doubling times (minutes)! See Table 3. 

TABLE 3. The effect of the discovery of three new bottles 

11.58 a.m. 

11.59 am. 

12.00 noon 

12.01 p.m. 

12.02 p.m. 

Bottle No. 1 is one quarter full 

Bottle No. 2 is half full 

Bottle No. 1 is full 

Bottle No. 1 and 2 are both full 

Bottle No. 1,2,3 and 4 are all full 

Quadrupling the resource extends the life of the resource by only two doubling times! When 

consumption grows exponentially, enormous increases are consumed in very short times! 

James Schlesinger, Secretary of Energy in the Carter administration in the United States of 

America noted that in the energy crisis ‘we have a classic case of exponential growth against a 

finite source’[41. 

LENGTH OF LIFE OF A FINITE RESOURCE WHEN THE RATE OF CONSUMPTION IS 

GROWING EXPONENTIALLY 

Thoughtful people would tend to agree that the world’s mineral resources are finite. The extent 

of the resources is only incompletely known, although knowledge about the extent of the 

remaining resources is growing very rapidly. 

For generations the consumption of resources has tended to grow steadily. The growth in consump 

tion has been driven by growing populations, by growing aspirations of individuals to consume 

and by the great growth ethic of our society. So it is natural to ask how long a resource wil last 

under conditions of steady growth. Let us plot a graph of the rate of consumption r(t) of a resource 

(in such units as tonnes/year) as a function of time measured in years. The area under the curve 

in the interval between times t = 0 (the present, where the rate of consumption is r,) and t = T 

wil be a measure of the total consumption C in tonnes of the resource in the time interval. We 

23


can fine the time Te at which the total consumption C is equal to the size of R of the resource 

and this time wil be an estimate of the expiration time of the resource. 

Imagine that the rate of consumption of a resource grows at a constant rate until the last of 

the resource is consumed, whereupon the rate of consumption falls abruptly to zero. It is appropriate 

to examine this model because this constant exponential growth is an accurate reflection 

of the goals and aspirations of our economic systems. Unending growth of the rates of production 

and consumption and of GNP is the central theme of our economies and it is regarded as 

disastrous when actual rates of growth fall below the planned rates. Thus it is relevant to calculate 

the life expectancy of a resource under conditions of constant rates of growth. Under these 

conditions the period of time necessary to consume the known reserves of a resource may be 

called the exponential expiry time (EET) of the resource. The EET is a function of the known 

size R of the resource, of the current rate of use ro of the resource and of the fractional growth 

per unit time k of the rate of consumption of the resource. The expression for the EET is derived 

in the Appendix where it appears as Eq. (6). This equation is known to scholars who deal in 

resource problems [ 51 and there is some evidence that it is beginning to be understood by some 

of the political, industrial, business and labour leaders who deal in energy resources. Certainly 

growth rates are now falling. For example the growth rate of electrical power consumption in 

the United States is now much lower than the 7 per cent annual rate that was predicted in 1975. 

This drop is the result of rapid price increases. The price increases and their effect on consumption 

were not anticipated as recently as 1975. 

HOW LONG WILL OUR FOSSIL FUELS LAST? 

The question of how long our resources will last is perhaps the most important question that 

can be asked in a modern industrial society. 

Dr. M. King Hubbert, the geophysicist, is a world authority on the estimation of energy 

resources and on the prediction of their patterns of discovery and depletion. Many of the data 

used here come from Hubbert’s papers and several of the figures are redrawn from figures in 

them [61. 

TABLE 4. World crude oil data. Units are lo9 barrels. 

Ultimate total production 1952 

Production to 1972 26 1 

Percentage of total production produced to 1972 13.4% 

Annual production 1970 16.7 

Note that by 1972 a little more than 1/8 of the world oil had been consumed. The ‘world 

petroleum time’ is between 2 and 3 minutes before noon, i.e. we are between two and three 

doubling times from the expiry of the resource. 

Table 4 gives statistics on world production of crude oil. Figure 1 shows the historical trend 

in world crude oil production. Note that from 1890 to 1970 the production grew at a rate of 

7.04 per cent per year, with a doubling time of 9.8 years. It is easy to calculate that the world 

reserves of crude oil would last 101 years if the growth in annual production was halted and 

production in the future was held constant at the 1970 level. Table 5 shows the life expectancy 

(EET) of world crude oil reserves for various rates of growth of production and shows the 

amount by which the life expectancy is extended if one adds world deposits of oil shale. Column 

4 is based on the assumption that the available shale oil is four times as large as the value reported 

24


by Hubbert. Note again that the effect of this very large hypothetical increase in the resource is 

very small. Figure 2 shows a dramatic model from Mario Iona [ 71 which can be used to represent 

the history of 7 per cent annual growth of world consumption of petroleum and to show the 

consequences of continuing the 7 per cent annual growth in the future. 

D 0 

C 

0 

.- 

U 0.1 

1880 1900 1920 1940 1960 1980 

Figure 1. History of World Crude Oil production (redrawn from Hubbert [6a]). The approximate straightline on this semilogarithmic 

graph shows that world oil production has grown steadily at a rate of a little over 7 per cent per year for nearly a 

century. 

This amount of oil must be 

discovered if we wash oil 

Consumption to continue to 

grow at 7 per cent per 

year for the decade 

2000 - 2010 

Figure 2. The 7 per cent solution (?) for world petroleum (Iona [7]). This representation presents a graphical answer to the 

question ‘How long could world petroleum consumption continue to grow at 7 per cent per year as shown in figure l?’ The 

area of each rectangle represents the quantity of petroleum consumed in the labelled decade. This makes it clear, as was seen in 

the example of the chess-board (table l), that if the doubling time is one decade, the consumption in any decade is equal to the 

total of all previous consumption. The area of the rectangle ABDC represents the known world petroleum resource. 

25


When consumption grows 7 per cent each year the consumption in any decade is approximately 

equal to the sum of all previous consumption, as can be seen by the areas representing 

consumption in successive decades. The rectangle ABDC represents all known 

that has been used in the past; the rectangle CDFE represents the new d 

made if we wish the 7per cent growth to continue for the decade from the year 

From these calculations, we can draw a general conclusion of great impmtzmce. When we are 

dealing with exponential growth, we do not need to have an accurate 0te of the size of a 

resource in order to make a reliable estimate of how long the resource 

TABLE 5. 

Col I 

Zero 

1% 

2% 

3% 

4% 

5% 

6% 

7% 

8% 

9% 

1 WO 

Life expectancy in years of various estimates of world oil reserves for different rates growth of annual 

production. Units are lo9 barrels. This table was prepared by using Eq. (6) with r, 

= 16.7 X lo9 

barrels/year. Column 1 is the percentage annual growth rate of production. Column 2 is the EET of 

the resource calculated using R = 1691 as the estimate of the amount of the remaining oil. Column 3 

is the EET calculated using R = 169 1 + 190 = 1881 representing crude oil plus shale. Column 4 is the 

EET calculated using R = 169 1 + 4( 190) = 245 1 which assumes that the amount of shale oil is four 

times the amount which is known now. 

Col 2 (year) 

101 

699 

55.3 

46.5 

40.5 

36.0 

32.6 

29.8 

27.6 

25.7 

24.1 

Col 3 (year) 

113 

75.4 

59.0 

49.2 

42.6 

37.8 

34.1 

312 

28.8 

26.8 

25.1 

Col 4 (yea) 

I47 

90.3 

68.5 

562 

48.2 

42.4 

38.0 

34.6 

31.8 

29.5 

27.5 

In a recent advertisement in papers and magazines in the United States a major American oil 

company said: ‘Vast oil potential in the U.S. untapped and unavailable’. The advertisement 

went on to note that ‘the United States may still have as much undiscovered and unproduced 

oil as has been used in our entire history’. The optimistic tone of the advertisement (the oil 

remaining is equal to all we have used) is negated by a simple understanding of what is meant 

by the fact that we have already used one half of the recoverable oil that was ever in the ground 

in the United States. The ‘oiltime’ is one minute before noon. 

As the reader ponders the seriousness of the situation and asks ‘What will life be like without 

petroleum?’ the thought arises of heating homes electrically or with solar power and of travelling 

in electric cars. A far more fundamental problem becomes apparent when one recognizes that 

modern agriculture is based on petroleum-powered machinery and on petroleum based fertilizers. 

This is reflected in the definition ‘Modern agriculture is the use of land to convert petroleum to 

food.’ 

NEWS ITEM (Exxon News [ 81 )‘United States agriculture is the most energy intensive in the 

world. From farm to ultimate consumer all of its activities account for about 15% of total United 

States energy consumption. Oil and gas combine to meet about 80% of agriculture’s energy needs. 

The petroleum and agriculture industries have been partners in making United States agriculture 

the most productive in the world. In 1850, the average American farmer could raise food for 

himself and four others. Today, such a farmer could feed himself and 59 others. By the year 

2000 he expects to feed himself and 95 others.’ 

26


TABLE 6. Major United States industrial users of petroleum products 

Farming 

Industrial 

Aviation 

Marine 

Railroad 

3.86 X lo7 tonneslyear 

3.47~ 107 

2.54 x 107 

1.96 x 107 

1.35 x 107 

~~ ~~~~ 

Think for a moment of the effect of petroleum on American life. Petroleum has made it 

possible for American farms to be operated by only a tiny fraction of the population; only one 

American in twenty-six lived on a farm in 1976. The people thus displaced from the farms by 

petroleum-based mechanization have migrated to the cities where the way of life is critically 

dependent on petroleum. The farms without the large number of people to do the work are also 

critically dependent upon petroleum-based mechanization. The approaching exhaustion of 

domestic reserves and the rapid depletion of world reserves of petroleum wil have a profound 

effect on Americans in the cities and the farms. It is clear that agriculture as it is known in the 

United States wil experience major changes within the life expectancy of most of us, and with 

these changes could come a major further deterioration of world-wide levels of nutrition. The 

doubling time (36 to 42 years) of world population (depending on whether the annual growth 

rate is 1.9 or 1.64 per cent) means that we have this period of time in which we must double 

world food production if we wish to do no better than hold constant the fraction of the world 

population that is starving. This would mean that the number starving at the end of the doubling 

time would be twice the number that are starving today. This was put into bold relief by David 

Pimentel of Cornel1 University in an invited paper read to the 1977 annual meeting of the 

American Association of Physics Teachers and the American Physical Society : 

As a result of overpopulation and resource limitations, the world is fast losing its capacity to feed itself. 

More alarming is the fact that while the world population doubled its numbers in about 30 years the world 

doubled its energy consumption within the past decade. Moreover, the use of energy in food production has been 

increasing faster than its use in many other sectors of the economy. 

An absolute upper limit for oil 

It is possible to calculate an absolute upper limit to the amount of crude oil the earth could contain. 

We simply assert that the volume of petroleum in the earth cannot be larger than the volume 

of the earth. The volume of the earth is 6.81 X lo2' barrels which would last for 4.1 X 10" 

years if the 1970 rate of consumption held constant with no growth. The use of Eq. (6) shows 

that if the rate of consumption of petroleum continued on the growth curve of 7.04 per cent per 

year of figure 1, this earth-full of oil will last only 342 years! 

Coal 

It has frequently been suggested that coal wil answer the United States and world energy needs 

for a long period in the future. What are the facts? 

Table 7 shows data on United States coal production that are taken from several sources. 

Figure 3 shows the history of coal production in the United States. Note that from 1860 to 1910, 

American coal production grew exponentially at 6.69 per cent per year (T2 = 10.4 year). The 

production then levelled off at 0.5 X 1 O9 tonnes/year which held approximately constant until 

1972 when the rate started to rise steadily. Coal consumption remained level for 60 years because 

the country's growing energy demands were met by petroleum and natural gas. In early 1976 

27


the annual coal production goals of the United States government were 1.2 X 10' tonnes for 

1980 and 2.1 X lo' tonnes for 1985. Consumption during 1976 was reported to be 0.60 X lo9 

tonnes and the administration of President Carter set the goal of raising annual coal production 

to 1 X 1 O9 tonnes by 1985 [ 91. From these data we can see that these goals called for an annual 

increase in United States coal production of over 5 per cent per year. 

r 

1 

L 

m 

ar 

>. 

a, 

C 

0 

10: 

10' 

[D 

P 10: 

2 

m 

L 

C 

0 

U 

0 

I) 

U 0 

a' 

IO" 

0' 

E x p i r a t i on of ' tot a I re source i nc I u d in g -* 

hypothetical' in the year 2000 

4 

/ 

-i 

Expiration of 'total identified 

resource' in the year 1987 

/ 

/ 

/ 

/ 

I 

Expiration of 'reserve base 

in the year 1966 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

f 

/-E,69 per cent per year 

i 

/ 

/ 

I I I 1 I I I 

1870 1890 1910 1930 1950 1970 1990 

Figure 3. History of United States coal production (redrawn from Hubbert [6a] 1. From the close of the American Civil War to 

about the year 1910, coal production grew steadily at a rate that averaged 6.69 per cent per year. Production then levelled off 

(with wide fluctuations) for 60 years and has now started to climb again. The crosses in the steep dashed curve at the right show 

the coal production targets set by the Ford administration while the circle in the lower dashed line represents the production 

goals of the Carter administration. The long dotted straight line shows what would have happened if the growth of consumption 

had not stopped or slowed in 1910. The three triangles mark the expiry times (EETs) of Averitt's three estimates of United States 

coal resources. Coal is an energy option for the United States in 1980 only because coal production had zero growth for 60 years 

following 1910. 

28

The energy cris@ 

TABLE 7. United States coal resource. Units are lo9 tonnes. 

Ultimate total production [6] 

High estimate 1486 

Low estimate 390 

Produced through 1972 (My estimate from Hubbert’s Figure 22) 

50 

Percentage of ultimate production produced through 1972 

Percentage of high estimate 3% 

Percentage of low estimate 13% 

Coal resource remaining 

High estimate 1436 

Low estimate 340 

Annual production rate, 1972 0.5 

Rate of export of coal, 1974 

0.06 



Table 8 shows the EETs of the high and low estimates of United States coal reserves for various 

rates of increase of the rate of production as calculated from Eq. (6). If we use the conservative 

smaller estimate of American coal reserves, we see that the growth of the annual rate of consumption 

will have to be held below 3 per cent if we want coal to last until 2076 A.D. If we want coal 

to last 200 years, the rate of growth of annual consumption wil have to be held below 1 per cent. 

TABLE 8. Lifetime in years of United States coal (EET). The lifetime (EET) in years of United States coal 

reserves (both the high and low estimate of the United States Geological Survey - USGS) are shown 

for several rates of growth of production from the 1972 level of 0.5 X lo9 tonnes per year. 

Zero 

1% 

2% 

3% 

4% 

5% 

6% 

7% 

8% 

9% 

1 W O 

11% 

12% 

13% 

High Estimate (yr) 

2872 

339 

203 

149 

119 

99 

86 

76 

68 

62 

57 

52 

49 

46 

Low Estimate (yr) 

680 

205 

134 

102 

83 

71 

62 

55 

50 

46 

42 

39 

37 

35 

One obtains an interesting insight into the problem if one asks how long beyond the year 1910 

could coal production have continued on the curve of exponential growth at the historic rate 

6.69 per cent per year of figure 3. The smaller estimate of United States coal would have been 

consumed around the year 1967 and the larger estimate would have expired around the year 

1990. Thus it is clear the use of coal as an energy source in 1980 and in the years to come is 

possible only because the growth in the annual production of coal was zero from 191 0 to about 

19 72! 

29


The current programme in the United States calls for increasing coal production in order to 

have enormous growth of coal exports. A study of the facts shows that raising coal exports now 

wil probably cause shortages of coal within the United States within one human lifetime. 

A WORD OF CAUTION 

We must note that these calculations of the EET of fossil fuels are not predictions of the future. 

They simply give first-order estimates of the life expectancies of known quantities of several fuels 

under the conditions of steady growth which our society and our government hold sacred. These 

estimates are emphasized as aids to understanding the consequences of any particular growth 

scenario that the reader might want to consider or to evaluate. 

The rate of production of our mineral resources will not rise exponentially until the EET is 

reached and then plunge abruptly to zero as modelled in these calculations and as shown in curve 

A of figure 4 even though our national goals are predicted on uninterrupted growth. The rate 

of production of our non-renewable mineral resources wil not follow the classic S-shaped transition 

from an early period of exponential growth to a horizontal curve representing a constant 

rate of production, curve B. Such a curve can be achieved in the production of renewable resources 

such as food, forest products, or the production of solar energy, provided the rate of production 

of the renewable resource is not dependent upon fossil fuels. Reference has already been made 

to the dependence of modern agriculture on petroleum, and as long as this dependence continues, 

the curve of agricultural production would be expected to follow curve C (the curve for nonrenewable 

petroleum) rather than curve B. Although the rate of production of mineral resources 

has been growing exponentially, one knows that at some time in the future the resources will be 

exhausted and the rate of production wil return to zero. Past history, this one future datum and 

a careful study of the rate versus time of production of resources that have expired has led 

Hubbert to the conclusion that the rate of production of a non-renewable resource will rise and 

fall in the symmetrical manner of a Gaussian curve as shown in curve C of figure 4. When he fits 

the data for United States oil production to a curve such as C, Hubbert finds that we are now just 

Te 

EET 

Figure 4. Three patterns of growth. Curve A represents steady exponential growth in the rate of production of a non-renewable 

resource until the resource is exhausted at T,, the exponential expiry time (EET). The area under the curve from the present 

(t = 0) to t = T, is equal to the known size of the resource. Curve C 

- 

represents Hubbert’s model of the way in which the rate of 

production of a non-renewable resource rises and falls. This model is based on studies of the rate of use of resources which have 

been nearly consumed. The area under this curve from the present to 1 = is equal to the size of the resource. Curve B represents 

the rate of production of a renewable resource such as agricultural or forest products where a constant, steady-state production 

can be maintained for long periods of time provided this production is not dependent on the use of a non-renewable resource 

(such as petroleum) whose production is following a curve such as C. 

30


to the right of the peak. We have used one half of the recoverable petroleum that was ever in 

the ground of the United States and in the future the rate of production can only go downhill. 

However until the late 1970s American demand for petroleum continued to grow exponentially 

and the difference between demands and production was made up by imports. Bold initiatives 

by the Congress could temporarily reverse the trend and could put a small bump on the downhill 

side of the curve. Alaskan oil can also put a little bump on the downhill side of the curve. 

The most dramatic conclusion that Hubbert draws from his curve for the complete cycle of 

United States oil production is that the consumption of the central 80 per cent of the resource 

will take place in only 67 years! 

It is sobering to face the downhill side of the curve and to note that in the past the rise in our 

annual consumption of energy per head has gone hand-in-hand with the increase in our standard 

of living. It is more sobering to note the close coupling between our production of food and our 

use of petroleum. It is even more sobering to note that as long ago as 1956 Dr. Hubbert addressing 

a large group of petroleum engineers and geologists said ‘According to the best currently 

available information, the production of petroleum and natural gas on a world scale wil probably 

pass its climax within the order of half a century, while for the United States the peak of production 

can be expected to occur within the next 10 or 15 years.’ (i.e. between 1966 and 197 1 .) 

We now know that that peak did occur in 1970! 

The United States is not alone in having reached the peak of production. There are signs that 

the Soviet Union may also be nearing that peak, if it has not already done so; and this is likely 

to be true of world production. 

MISREPRESENTATIONS OF THE ENERGY PROBLEM 

We have now established the critical background of facts and information that are needed to 

understand the energy problem and can turn our attention to public representations of the 

pioblem. 

The most common misrepresentation in the news and other reports on energy is to quote the 

life expectancy of a resource based on the assumption of zero growth. This assumes that rate of 

consumption (tonnedyear) wil not grow above the present rate until the resource is exhausted. 

Sometimes the assumption is stated explicitly as, for example, in Simon [ 101 : ‘We have half of 

all the coal reserves in the non-communist world, of which at least 425 X lo9 tonnes are immediately 

recoverable. At 1973 levels of consumption we have enough for 800 years.’ 

Sometimes the assumption is not stated as in an advertisement by the American Electric Power 

Company which claimed in 1975 [ 111 : ‘We are sitting on half of the world’s known supply of 

coal - enough for 500 years.’ 

Sometimes the assumption is stated but then rapid growth (which invalidates the assumption) 

is predicted or advocated. Here are quotations from an advertisement by the Exxon Corporation 

in 1975 [ 121 : ‘At the rate the United States uses coal today, these reserves could help keep us in 

energy for the next 200 years. . . . Most coal used in America today is burned by electric power 

plants. . . . (which). . . . consumed about 400 million tons of coal last year. By 1985 this figure 

could jump to nearly 700 million tons.’ 

It is obviously and demonstrably misleading to tell people that coal or some other nonrenewable 

resource, will last for x centuries ‘at present rates of consumption’ when it is a matter 

of blind faith that the United States and world economies must maintain steady growth of the 

31


consumption of these resources endlessly into the future. Furthermore, one must recognize that 

the energy cost of producing a unit of fossil fuel energy increases as the reserves are depleted. So 

the net energy represented by a tonne of coal or of crude oil will generally decline into the future. 

Thus even if the fossil fuel were produced in the future ‘at present rates’, the net energy available 

to society from this production would decline. As noted by Odum [ 131 : ‘Scenarios based on 

gross reserves overestimate the time the reserves wil last. Scenarios should be based on net 

energy, that is energy yield minus that needed to collect and process the energy.’ 

It is vital that we point out this ‘Most Common Misrepresentation’ to our students so that they 

can recognize it and can appreciate that the misrepresentation gives life expectancies which are 

longer (often by an order of magnitude) than the Exponential Expiry Times calculated for 

reasonable current and anticipated rates of growth of production. We must also point out the 

importance of the concept of net energy in estimating the lifetime of fossil fuel reserves. 

Our students must recognize that, in response to legitimate technical questions, we wil be 

given answers which sound impressive but which, on close examination, are seen to bear no 

relation at all to the question. This is well illustrated in a discussion in US. News and World 

Report (13 August, 1979, p.35): 

However gasohol has many critics who focus on its hgh costs and claim that it results in a net loss of energy. 

‘You’re making alcohol that generates less energy when burned than it took to make it’ argues a distillery official. 

Advocates respond that the price gap between gasoline and gasohol narrows with each increase in oil prices; mass 

production of alcohol wil make it even cheaper, they contend. 

Note that the ‘answer’ bears no relation to the question. 

WHAT DO WE DO NOW? 

The problems are such that we have rather few options. All of the following points are vital: 

(i) We must educate all of our people to an understanding of the arithmetic and consequences 

of growth, especially in terms of population and in terms of the earth’s finite resources. David 

Brower [ 141 has observed that ‘the promotion of growth is simply a sophisticated way to steal 

from our children.’ 

(ii) We must educate people to the critical urgency of abandoning our almost religious 

belief in the disastrous dogma that ‘growth is good’, that ‘bigger is better’, that ‘we must grow 

or we will stagnate’, etc. We must realize that growth is but an adolescent phase of life which 

stops when physical maturity is reached. If growth continues in the period of maturity, it is 

called obesity or cancer. Prescribing growth as the cure for the energy crisis has all the logic of 

prescribing increasing quantities of food as a remedy for obesity. 

(iii) We must economize in the use and consumption of everything. We must recognize that, as 

important as it is to economize, the arithmetic shows clearly that large savings from that action 

wil be wiped out in short times by even modest rates of growth. For example, in a dozen or so 

years a massive federal programme might result in one half of the heat for the buildings where we 

live and work being supplied by solar energy instead of by fossil fuels. This would save 10 per 

cent of our national use of fossil fuels, but this enormous saving could be completely wiped out 

by two years of 5 per cent growth! Conservation alone cannot do the job! The most effective 

way to conserve is to stop the growth in consumption. 

(iv) We must re-cycle almost everything. Except for the continuous input of sunlight, the 

32


human race must finish the trip with the supplies that were aboard when the ‘spaceship earth’ 

was launched. 

(v) We must invest great sums in research (a) to develop the use of solar, geothermal, wind, 

tidal, biomass and alternative energy sources; (b) to reduce the problems of nuclear fission power 

plants; (c) to explore the possibility that we may be able to harness nuclear fusion. These investments 

must not be made with the idea that if these research programmes are successful the new 

energy sources could sustain growth for a few more doubling times. The investments must be 

made with the goal that the new energy sources could take over the energy load in a mature and 

stable society in which fossil fuels are used in a declining exponential curve as chemical raw 

materials and are not used as fuel for combustion. One great area of responsibility of our 

community of scientists and engineers is vigorous pursuit of research and development in all these 

areas. These areas offer great opportunities to creative young people. 

Perhaps the most critical thing we must do is to decentralize and consequently humanize, the 

scale and the scope of our national industrial and utility enterprises [ 151 . 

(vi) We must recognize that it is exceedingly unscientific to promote ever-increasing rates of 

consumption of our fuel resources based on complete confidence that science, technology and 

the economics of the market-place wil combine to produce vast new energy resources as they 

are needed. 

The most recent major new energy source that scientists discovered was nuclear fission. Fission 

was discovered in 1939. The operation of a nuclear reactor was demonstrated in 1942. The first 

commercial nuclear power stations date from the 1950s and in the United States and in the 

United Kingdom over 10 per cent of electric energy is obtained from nuclear reactors. The great 

progress that has been made in the forty years since the discovery of fission has demonstrated 

that nuclear power systems are costly and complex. It seems safe to guess that any new source 

of energy that might emerge from the laboratory wil be even more costly and complex. This 

wil mean that the time scale with which a hypothetical new source of energy could take over the 

energy load of the United States wil be even longer than it has been for fission. 

Fusion is most commonly mentioned as being an unlimited energy source. The optimism that 

leads some people to believe that fusion power wil be ready whenever it is needed should be 

balanced against this opening statement in a report on fusion from the Massachusetts Institute 

of Technology (MIT): ‘Designing a fusion reactor in 1977 is a little like planning to reach heaven: 

theories abound on how to do it, and many people are trying, but no one alive has ever suceeded’ 

1161. 

(vii) We can no longer sit back and deplore the lack of leadership and the lack of response of 

our political systems. The arithmetic makes clear what wil happen if we hope that we can 

continue to increase our rate of consumption of fossil fuels, Some experts suggest that the system 

wil take care of itself and that growth will stop naturally, even though they know that cancer, if 

left to run its natural course, always stops when the host is consumed. My seven suggestions are 

offered in the spirit of preventive medicine. 

WHAT MUST PHYSICS TEACHERS DO? 

For decades physics teachers throughout the world have discussed the RC circuit and the decay 

of radioactive nuclei and have thus introduced the simple differential equation that gives rise 

to exponential decay of the charge on the capacitor or of the number of radioactive nuclei 

remaining. These provide a wonderful opportunity to digress and to point out that exponential 

33


arithmetic has great value outside these two special examples and to show our students that 

exponential arithmetic is probably the most important mathematics they wil ever see. It is 

especially important for students to see how the change in the sign of the exponential can make 

an enormous difference in the behaviour of the function. But we wil need to do more. We must 

integrate the study of energy and of the exponential arithmetic into our courses [ 171 . In addition 

we have an even larger task. As science teachers, we have the great responsibility of participating 

constructively in the debates on growth and energy. We must be prepared to recognize opinions 

such as the following, which was expressed in a letter to me that was written by an ardent 

advocate of ‘controlled growth’ in our local community: ‘I take no exception to your arguments 

regarding exponential growth. . . .. I don’t think the exponential argument is valid on the local 

level.’ 

We must bring to these debates the realism of arithmetic and the new concept of precision in 

the use of language. We must convey to our students the urgency of analysing all that they read 

for realism and precision. We must convey the importance of making this analysis even when 

they are reading the works of eminent national figures. In the following example, such a figure 

was writing in one of the world’s most widely circulated magazines. (The emphasis in the quotations 

is in the original.) 

The simple truth is that America has an abundance of energy resources. 

An estimated 920 trillion (10l2) cubic feet of natural gas still lies beneath the United States. Even at present 

consumption rates, this should last at least 45 years. 

About 160 billion (lo9) barrels of oil still lie below ground or offshore. That’s enough to last us into the next 

century at present rates of consumption [ 181. 

When students analyse these statements they can see that the first is false if ‘abundance’ 

means ‘sufficient to continue currently accepted patterns of growth of rates of consumption 

for as long as one or two human lifetimes’. An evaluation of the second and third statements 

shows that they are falsely reassuring because they suggest the length of time our resources 

wil last under the special condition of no growth in the rates of use. The condition of no growth 

in these rates is contrary to the precepts of a growth-oriented society. It is completely misleading 

to introduce the results of ‘no growth’ unless one is advocating ‘no growth’. 

If it is true that United States natural gas reserves wil last 45 years at present rates of consumption 

(R/ro = 45 years) then Eq. (6) shows that this amount of gas would last only 23.6 

years at an annual growth rate of 5 per cent, and only 17 years at an annual growth rate of 10 

per cent. 

When the third statement is analysed one sees that the given figure of 160 X IO9 barrels of 

reserves is roughly 60 per cent greater than Hubbert’s estimate. This amount would last 49 years 

if oil was extracted at the 1970 rate of 3.3 X IO9 barrels/year, held constant with no growth. 

However, United States domestic consumption is now roughly twice the rate of domestic production, 

so this amount of oil would satisfy domestic needs for only about 25 years if there was 

no growth in those domestic needs. If R/ro = 25 years, then Eq. (6) shows that this amount of oil 

would last only 16.2 years if consumption grew 5 per cent per year and only 12.5 years if it grew 

10 per cent per year. 

We can conclude that the author is probably advocating growth in the rate at which we use 

fossil fuels from the following imprecise statement, ‘The fact is that we must produce more 

energy’. Therefore the author’s statements about the life expectancy of resources at current rates 

34


of use are irrelevant. When they are offered as reassurance of the lack of severity of our energy 

problem, they can seem to be dangerously and irresponsibly misleading. 

Students should be able to evaluate the same author’s statement about coal: ‘At least 220 

billion tons of immediately recoverable coal awaits mining in the United States.’ This ‘could 

supply our energy needs for several centuries.’ 

Students can see that the size of the coal reserves given by the author is smaller than either 

of the two estimates given by Hubbert. They can see that it is imprecise and meaningless to 

suggest how long a resource wil last if one says nothing about the rate of growth of production. 

In addition to encouraging our students to carry out their responsibility to analyse what they 

read, we must encourage them to recognize the callous (and probably careless) inhumanity of a 

prominent person who is perhaps in his fifties [ 181, offering reassurance to younger readers to 

the effect, ‘don’t worry, we have enough petroleum to last into the next century’. The writer 

is saying that ‘There is no need for you to worry, for there is enough petroleum for the rest of 

my life’. Can we accept the urgings of those who advocate unending expansion and growth in 

the rates of consumption of our fossil fuels and who say Why worry, we have enough to last 

into the next century’? 

We must give our students an appreciation of the critical urgency of evaluating the vague, 

imprecise and meaningless statements that characterize so much of the public debate on the 

energy problem. The great benefits of the free press place on each individual the awesome responsibility 

of evaluating the things that he or she reads. Students of science and engineering have 

special responsibilities in the energy debate because the problems are quantitative and therefore 

many of the questions can be evaluated by simple analysis. 

Speaking recently, Dr. Hubbert noted that we do not have an energy crisis, we have an energy 

shortage. He then observed that the energy shortage has produced a cultural crisis. 

We must emphasize to our students that they have a very special role to play in our society, a 

role that follows directly from their analytical abilities. It is their responsibility (and ours) to 

become great humanists. 

Acknowledgements 

A great deal of correspondence and hundreds of conversations with dozens of people over six 

years have yielded many ideas, suggestions and facts which I have incorporated here. I offer 

my sincere thanks to all who have helped. I am deeply indebted to E.J. Wenham for his work 

and patience in preparing this manuscript for publication. 

35


APPENDIX 

When a quantity such as rate r(t) of consumption of a resource grows a fixed percentage per 

year, the growth is exponential. 

where Y, is the current rate of consumption at t = 0, e is the base of natural logarithms, k is the 

fractional growth per year, and t is the time in years. The growing quantity wil increase to twice 

its initial size in the doubling time T2 where 

T2 (yr) = (ln2) / k = 70/P, (Eq. 2) 

and where P, the percentage growth per year, is 100k. The total consumption of a resource 

between the present (t = 0) and a future time Tis 

=l C r(t) dt. 

The consumption in a steady period of growth is 

C = rol ekTdt 

If the known size of the resource is R tonnes, then we can detennine the exponential expiry 

time (EET) by finding the time T, at which the total consumption C is equal to R: 

We may solve this for the exponential expiry time T, , 

R = (r0/k)(ekT, - 1). 0%. 5) 

EET = T, = (l/k) In (kR/v, + 1). (Eq. 6) 

This equation is valid for all positive values of k and for those negative values of k for which the 

argument of the logarithm is positive. 

36


REFERENCES 

1. This article originally appeared in the American Journal of Physics, Vol. 46, No. 9, September 1978, pp. 

876-88 and is printed here in modified form. 

2. General Electric Co. (advertisement).Newsweek, 21 July 1975, p. 1. 

3. BROWN, L., quoted in Newsweek, Vol. 88, No. 23,6 December 1976, p. 58. 

4. SCHLESINGER, J., quoted in ‘Opening the Debate’, Time, Vol. 109, No. 17,1977, pp. 27-32. 

5. VAN ENGELHARDT, W. et al. EnvironmentalGeology, Vol. 1,1976, pp. 193-206. 

6. (a) HUBBERT, M.K. A National Fuels and Energy Policy Study, Serial 93-40 (92-75) Part 1, Washington, 

D.C., U.S. Government Printing Office, 1973; (b) M.K. HUBBERT, ‘Survey of World Energy Resources’ in: 

L.C. RUEDISILI and M. FIREBAUCH (eds.), Perspectives on Energy, New York, Oxford University Press, 

1975; (c) M.K. HUBBERT, Resources and Man, San Francisco, Calif., Freeman, 1969; (d) M.K. HUBBERT, 

The Energy Resources of theEarth, San Francisco, Calif., Freeman, 197 1 (reprinted from Scientific American 

(New York), Vol. 225, No. 3, September 1971, p. 60-70). 

7. IONA, M. Physics Teacher, Vol. 15, No. 6,1977, p. 324. 

8. Exxon News. ‘U.S. Agriculture - Largest Petroleum Consumer’, 1978. 

9. Newsweek, 31 January 1977. 

10. SIMON, W.E. A Time for Truth. New York, Reader’s Digest Press, 1978. 

11. American Electric Power Co. Inc. (advertisement). Newsweek, 20 October 1975. 

12. Exxon Corporation (advertisement). Newsweek, 21 July 1975. 

13. ODUM , H.T. et al. Middle and Long-Term Energy Policies and Alternatives, Part 1: Hearings Before the Us. 

House of Representatives Committee on Interstate and Foreign Commerce, 94th Congress, 25-26 March 

1976. Washington, D.C., U.S. Government Printing Office. (Serial No. 94-63). 

14. BROWER, D. Not Man Apart (San Francisco, Calif.), Vol. 6, No. 20, November 1976. 

15. LovmS, A. Soft Energy Paths: Towardsa Durable Peace. Cambridge, Mass., Ballinger, 1977. 

16. Technology Review, December 1976, p. 21. Reprinted in 2nd edition of L.C. RUEDISILI and M. FIREBAUGH 

(eds.), Perspectives on Energy, New York, Oxford University Press, 1975. 

17. As examples of new texts in which this is done, see R.H. ROMER, Energy -An Introduction to Physics, San 

Francisco, Calif.,Freeman, 1976 and Association for Science Education, Science in Society - Teacher’s 

Guide, London, Heinemann Educational, 1981. 

18. LAIRD, M. The Energy Crisis:Made in USA. Reader’s Digest, September 1977, p. 56. 

37


Measures of energy and power in terms of solar input 

A. P. FRENCH 

This short note is based on an article by A. Rose entitled ‘A Global View of Solar Energy in 

Rational Units’.’ Rose points out that most measures of energy are presented in units that have 

little or no meaning even for the technically trained reader, He proposes a simple scale based on 

the solar unit - a unit of power: ‘1 solar unit equals the solar power striking the earth, averaged 

throughout the day and throughout the year’. 

The solar unit is elastic in the following sense: if applied to the whole earth, it is the average 

solar power striking the whole earth’s surface. If applied to just a part of the earth (e.g. the 

United States) it equals the average solar power falling on that part of the earth. The world 

average of one solar unit is about 200 watts per square metre.2 

The generation and use of power by humans is added to the solar input. This will raise the 

mean temperature of the earth, or of particular portions of the earth, because the mean temperature 

is the result of a balance between the energy being received or generated at the earth’s surface 

and the energy being radiated away into space. Actually these man-produced changes of mean 

temperature are very tiny - it would be disastrous if it were otherwise - but the solar input still 

provides a very convenient measuring stick with which other energy sources or consumptions can 

be compared. 

The present mean temperature of the earth is close to the freezing point of water. This is just 

about what one would expect theoretically from the balance between radiation loss and one 

solar unit of input. Now suppose that world energy generation added a second solar unit of input. 

What would happen to the mean temperature? The answer is that it would rise close to the 

boiling point of water, and almost all life would be eliminated. What if world energy generation 

were one tenth of a solar unit? This would produce a world-wide temperature rise of about 

8°C. Regarded simply as a temperature rise, this would not be disatrous for life in general; it 

would simply imply a tropical climate for most regions. But it would be intolerable because the 

1. A. Rose, ‘A Global View of Solar Energy in Rational Units’, Physica Status Solidii (A). Applied Research, Vol. 56, 1979, 

p. 11-26. 

2. The solar power input at the earth’s surface is less than that measured by spacecraft in orbit above the earth’s atmosphere 

which plays a major role in the reflection, absorption and reemission of the radiation. 

38

A solar unit 

polar ice caps would melt and shorelines everywhere would be inundated. (Actually, however, 

the power consumption in major metropolitan areas is in some cases of the order of 0.1 solar 

unit over those areas - and their mean temperatures are raised by several degrees in consequence. 

New Yorkers keep their whole city warm!) 

Moving down the scale, we now come to situations that are less hypothetical. If world-wide 

power generation were equivalent to 1/100 of a solar unit, the world mean temperature would 

rise by about 1 K. As Rose says, ‘At this point, experts may disagree on whether such a temperature 

rise would have major effects on the ice caps, the cloud cover, the weather patterns and the 

distribution of plant and animal life. Whatever the arguments may be, pro or con, it is not the 

sort of experiment the world should choose to explore.’ Yet such a temperature rise appears to 

be the likely consequence, through the greenhouse effect, of continuing to increase the carbon 

dioxide content of the atmosphere by the burning of fossil fuels at their present rate for another 

century or so. 

Going down another factor of 10, we have l/lOOO of one solar unit. This corresponds to the 

present level of power generation in the United States. That is, the total power now generated 

in the United States is equal in amount to 0.1 per cent of the total solar radiation falling on the 

country. 

For the world as a whole, the total power generated is at present only 1/10 000 of a solar 

unit - i.e. the equivalent of 0.01 per cent of all the solar power received by the earth. However, 

there are at least two factors operating to increase this figure. First, the population of the world 

is continuing to increase at a rapid rate, and seems destined to double, or more, within much 

less than a century. Second, the urge toward a higher standard of living wil certainly cause the 

energy usage per person in the developing countries to rise and perhaps to approach the United 

States level. It is thus not at all unlikely that global energy production and use wil come to 

exceed 1/1000 of a solar unit, and will be enough to create concern about climatic changes of 

the sort mentioned above. 

The magnitude of this projected global demand for energy suggests that, rather than accepting 

it as a need that must somehow be supplied, we ought to look very critically at the way 

energy is squandered in a high-technology society. Albert Rose, after presenting the above 

estimates, points out that the ‘good life’ in the United States involves an average power usage 

of about 10 kilowatts per person, whereas only about 100 watts is needed to keep the human 

machine going (equivalent to one medium power light bulb). Thus North American society 

uses the energy equivalent of 100 servants for eaeh citizen - a hundred times the energy we 

need to stay alive. In Rose’s words, ‘flipping on a 100 W bulb is the energy equivalent of adding 

another servant. Stepping on the accelerator of an automobile in anticipation of a green light 

calls forth the equivalent of over 1000 servants pushing on the rear end of the car and would 

have been the envy of any Pharaoh.’ It is obvious that any significant retreat from this lavish 

existence would be strongly resisted by any society that now enjoys it. Indeed, the present 

predictions are that the demand for electrical power in the United States will double in the 

next decade or so. But, if humanity as a whole is to aspire to a comfortable standard of living, 

we had better watch those solar units - and the ‘haves’ must be prepared to make some concessions. 

39


Entropy and information 

R. U. SEXL AND A. PFLUG 

WHO IS AFRAID OF ENTROPY? 

Among the many quantities used in physics, such as energy, momentum, electrical charge or 

temperature, there is one which has often been considered to be somewhat mysterious and hard 

to understand: entropy. It is interesting to ask why entropy acquired this reputation. 

The first reason is that entropy - unlike energy, electrical currents or velocities - plays no 

important role in everyday life. Second, in contrast to energy or momentum, entropy is not a 

conserved quantity which would remain constant in all possible physical processes. On the 

contrary, entropy generally increases in the course of time. Finally there is no piece of experimental 

equipment which could be used to measure the entropy of a body directly. The entropy 

is a ‘theoretical concept’ which can be calculated only with the help of a specific heat according 

to the well-known relation 

Here dS denotes the increase in entropy of a body when the amount of heat dQ is supplied 

at the temperature T, and c is the corresponding specific heat. [ 11 

What are the motivations for this strange definition of entropy? In (Eq. 1) a quantity has been 

defined which is capable of describing the direction of all thermodynamic processes. In this 

respect entropy is the characteristic quantity of thermodynamics, since only in this sub-field of 

physics are the two directions of time not equivalent. 

The considerations which follow aim to suggest an approach to the concept of entropy which 

wil lead to an intuitive understanding of this physical quantity, comparable to the ‘feeling’ one 

usually has for charge, temperature or energy. In many cases our ‘feelings’ about these quantities 

can be used to derive qualitative statements about the behaviour of a physical system even without 

details and exact calculations. 

A suitable approach starts from one of the most important scientific concepts of our century, 

the concept of information. It was the discovery of Claude Shannon and Norbert Wiener that 

40

Entropy and Information 

information can be measured (at least in part) and thereby made into a metric concept, which 

can be dealt with mathematically [2]. This led to a new discipline, information theory, which 

turned out to be of great relevance for mathematics and science [ 31 . From an educational point 

of view the relevance of the new concepts lies in the fact that a number of surprising insights 

into the behaviour of systems and processes is possible with elementary mathematical means. 

This is in marked contrast to many other areas of mathematics which are used in schools for the 

solution of rather trivial problems with great mathematical effort. 

The metrical, quantitative concept of information wil be applied to thermodynamic systems 

in the second part of this paper. It is a characteristic property of these systems that the positions 

and velocities of the individual molecules are not known in detail. This lack of information is - 

up to a trivial factor - the mysterious entropy. 

INFORMATION CAN BE MEASURED 

In order to make information a metric concept we need a suitable unit of information. This unit 

is the ‘bit’. It corresponds to the information contained in the answer to a question such as: 

‘Up or down?’; ‘Yes or no?’; ‘To be or not to be?’. One bit of information allows one to distinguish 

between two possibilities, which can be symbolized by the numbers 0 and 1, for example. 

Two bits of information allow one to distinguish between four possibilities and three bits 

contain the information describing eight possible events (see figure 1). 

Figure 1. 

The number n of ‘yes - no’ questions needed for distinguishing between N different cases. 

The general result is that: 

n bits of information are required to distinguish between N = 2n events. 

This relation can also be written in the form 

log N 

n = iog, N = - log n 

We shall restrict ourselves here however to examples which require no knowledge of logarithms 

in order to restrict the mathematical requisites to a minimum. This wil enable us to deal with 

41


some simple cases only, in which all events considered occur with equal probability. Despite this 

restriction we will, however, be able to deal with a number of very interesting and relevant 

examples from various sciences [ 41 . 

With the definition given above, we can discuss several relevant examples of information 

storage. Table 1 gives the number of bits contained in various sources of information. 

TABLE 1. Information content of the ‘letters’ of various sources of information 

Alphabet N=32 n=5 

Genetic code N=4 n=2 

Numbers N= 10 n = 3.32 

- 

According to this table, one letter of the alphabet contains five bit of information and an average 

word - containing six letters - corresponds to thirty bit. For simplicity, we have assumed here 

that all letters in the alphabet occur with equal probability. Only in this case can our result 

(Eq. 1) be applied. If this is not the case - or if the sequence of letters contains correlations - 

the amount of information contained in one letter is less than the result indicated above. This 

leads to interesting questions of redundancy, which wil not be dealt with here [ 5 I . 

A different type of alphabet is contained in the genetic code [6]. The genetic information 

contained in DNA is encoded into the sequence of the four different bases (thymine, adenine, 

cytosine, and guanine). One base corresponds to two bit of information, since there are four 

different possibilities. The double helix of Drosophila (the fruit-fly) is a giant molecule with 

a length L = 1.2 cm. Each of its subunits containing two bit of information has a length of 

approximately 1 = 1.2 X lU7 cm. The total information contained in the genetic code of 

Drosophila is thus 

n = 2L/Z = 2 X lo7 bit. (Eq. 3) 

In a similar way the information content of various other organisms can be calculated (see 

Table 2). With the help of Table 1, we can translate this into various other types of information. 

How many pages are needed for a ‘build-your-own-man’ book? If one page has 30 lines with 70 

characters to a line then its information content is 

TABLE 2. Information content of various organisms 

Organisms 

Virus 

Drosophila (fruit fly) 

Mm 

n (1 page) = 30 X 70 X 5 = lo4 bit. (Eq. 4) 

Information 

2 X lo4 bit 

2 X lo7 bit 

lo9 bit 

Thus the genetic information contained in a virus corresponds to two pages, while for Drosophila 

2000 pages are needed and for a man lo5 pages, i.e. the content of about 500 books. It is rather 

surprising that so little information is needed to build a virus. Maybe this can help in understanding 

how life originated. 

This result brings us to one of the most important technical problems in communication 

theory. If we want to communicate information at a great rate - as is required by modern 

42


society - one has to switch currents off and on as fast as possible. In each half wave of an alternating 

current, one bit of information can be stored (whether or not the half wave is at full 

amplitude). Therefore, the feasibility of communication networks was linked historically to the 

progress of high-frequency technology. The highest requirements are posed by television. Each 

television picture consists of, say, 500 lines containing 600 points each, i.e. a total of 3 X 10’ 

points. If we assume, for the sake of simplicity, that each point can be either black or white, the 

total information content of one picture becomes 3 X IO5 bit. Since 25 pictures have to be 

transmitted per second, the total information flow becomes 7.5 X lo6 bit/s. From this we can 

easily calculate the band width required for the transmission of television pictures. Since each 

bit corresponds to a half wave, the total band width becomes 

Af=?hX7.5X 106/s~4MHz. 

The frequency f of the carrier signal should be at least f x l0OAf~ 400 MHz. From the relation 

fX=c we can now calculate the wavelength used in television: 

X=c/f= 3 X i08ms-l/4 X lo8 s-l x 1 m. 

Returning to our examples from biology we can calculate to how many seconds of television 

commercials the genetic information contained in man corresponds. Since roughly 1 O7 bit can 

be transmitted per second we obtain for the time T needed: 

lo7 bit/s X T = lo9 bit or T= 100 s. 

Therefore it would take about two minutes to transmit the genetic make-up of man in the form 

of a television commercial. 

In another example using television we can check the proverb: ‘A picture says more than a 

thousand words.’ One word contains about 30 bit of information, if we assume that it consists 

of six letters. Therefore the information contained in 1000 words is 3 X lo4 bit. Bearing in mind 

that one television picture contains about 3 X lo5 bit, it follows that one picture corresponds 

to roughly 10 000 words (or about 30 pages). 

In conclusion, we refer to another problem which can also be solved with the help of information 

theory. Of twelve balls, one ball is either heavier or lighter than the other eleven balls. The 

object is to find out, using a balance, which ball is the odd one out and whether it is heavier or 

lighter than the rest. This problem is clearly one of missing information, which is to be gained by 

using the balance. How many times do the balls have to be weighed in order to supply the missing 

information? 171. 

ENTROPY AND INFORMATION 

With the help of the metric concept of information we can characterize the information missing 

about thermodynamic systems. While a detailed knowledge of the initial positions and velocities 

of all mass points contained in an n-body problem is assumed in mechanics, the exact positions 

and velocities of the numerous molecules contained in a gas or another thermodynamic system 

are never known exactly. This lack of information about thermodynamic systems is described 

by entropy. 

At first it might seem that the lack of knowledge about the initial conditions of the molecules 

43


contained in a gas, liquid or a solid is due only to the laziness of experimental physicists. It would 

be most useful to have more detailed information about these systems, as the following example 

shows. About 2000 years ago the famous Iibrary of AIexandria was destroyed by a fire annihilating 

many unique works of ancient Greek and Roman literature. Couldn't the physicist help the 

historian here in reconstructing the contents of this Iibrary by measuring the positions of the 

individual smoke particles, which should still be contained in our atmosphere? From this 

knowledge one could calculate backwards in time and reconstruct the contents of the lost manuscripts 

exactly. In such a calculation the exact information about the position of the various 

molecules is obviously relevant since the reconstruction of the average position of letters in the 

ancient manuscripts would not be very helpful. 

Unfortunately it turns out very soon that physicists are Iousy historians. The initial position 

x and the initial momentum p of each molecule can only be determined with an accuracy compatible 

with the Heisenberg uncertainty relation Ax Ap -itit. An attempt to calculate - starting 

from the initial conditions - even the first collision of each molecule fails immediately, since 

the highest accuracy compatible with the uncertainty relation prevents a calculation of even 

this very first collision which takes place (under normal conditions) on the average after lo-' s. 

With the best possible choice of the initial conditions for position and momentum of each 

molecule the final position (Figure 2) at the end of the mean free path length L can be predicted 

only with the accuracy [ 81 

ax, =- 

I 

0 

0 

0 

0 

0 

0 

0 

0 0 

0 

Figure 2. Already the first collision between two selected molecules in a gas cannot be predicted exactly due to the Heisenberg 

uncertainty relation. 

44


Inserting L X lo-’ m, p % kg m/s we obtain Axl = 10- m. The uncertainty at the first 

collision is thus about 10 times the diameter of a molecule so that the specific molecule aimed at 

wilI be hit only with a probability of about 1 per cent. The detailed, molecular processes occuring 

in a gas are thus CO etely undetermined after lom9 s and each repetition of an experiment 

- starting from the same initial conditions - wil lead to a completely different course of events, 

when detailed questions about the positions and velocities of molecules are asked. The same 

applies to any attempt to trace the past positions of molecules. Physicists therefore turn out to 

be very poor historians, who cannot even calculate details over a timespan of s when dealing 

with individual molecules in a gas. 

Any attempt to obtain detailed information about the individual positions of molecules in a 

gas is therefore completely useless. A precise prediction of detailed events, corresponding to the 

ideals of classical physics, is impossible in principle. It is thus necessary to restrict oneself to 

‘ensembles’ of thermodynamic systems which have the same macroscopic properties but differ 

in their individual molecular details. 

The simple arguments given here have shown the futility of all attempts of detailed calculations 

concerning thermodynamic systems. They show that the lack of knowledge about molecular 

details lead in general to a further decrease of the available information in the course of time [91 . 

These preliminary considerations enable us now to introduce the concept of entropy. Entropy 

is a measure of the missing information about the molecular details of gases or other thermodynamic 

systems and is defined as follows: 

The entropy S of a thermodynamic system is given by 

S = 0.7 X k X (missing information) (Eq. 6) 

In this relation the missing information is measured in bit and k is the Boltzmann constant 

(1.38 X J/K). The conversion factor 0.7k (more accurately k ln2) between information and 

entropy wil turn out to be convenient [ lo]. 

IRREVERSIBLE PROCESSES 

I 

I 

‘The passage of heat from a colder to a hotter body cannot take place without compensation.’ 

Starting from this apparently trivial statement, Rudolf Clausius was able to prove in 1865 the 

existence of a function of state S - the entropy - for every thermodynamic system [ 11 I . His 

argument showed furthermore that the entropy remains constant for reversible processes in 

isolated systems and increases during irreversible processes. From the point of view of information 

theory, this increase of entropy corresponds to a loss of information about the thermodynamic 

system as the following examples wil show. 

As a first example of a typical irreversible process we consider the expansion of a gas into a 

vacuum (see figure 3). During this process information is lost. Before the expansion we were 

able to answer the question: ‘Left or right?’ for each molecule. After the expansion this is no 

longer possible. Therefore one bit of information is lost for each molecule, leading to a decrease 

of N bit of information available about the thermodynamic system. The corresponding increase 

of entropy is 

AS = 0.7 k N. 0%. 7) 

A similar loss of information occurs when two gases consisting of N/2 molecules each are 

45


Ltherrna I 

insule ition d 

Figure 3. Irreversible expansion of a gas into a vacuum. 

Figure 4. Reversible expansion of a gas into a vacuum. 

mixed. When the wall separating the two gases is removed, N bit of information are lost since the 

question concerning the type of molecule (gas A or gas B) can no longer be answered by simple 

macroscopic means. 

These two examples indicate that irreversible processes are always connected with a loss of 

information which is described thermodynamically by the increase of entropy. 

Finally we have to give the reasons for the choice of the special factor of proportionality, 

0.7 k, in the definition of entropy. For this purpose we consider a gas in contact with a heat 

reservoir with temperature T. This gas can be expanded to twice .its volume by slowly moving 

a piston outward (figure 4). The initial and the final conditions of this reversible process are the 

same as for the irreversible process (figure 3) considered before. In both cases the volume of the 

gas doubles while the temperature remains constant. The increase of entropyAS = 0.7 X k X N is 

thus the same in both cases. 

During the reversible process, the total entropy of the gas and the heat reservoir has to remain 

constant. Thus not only the heat AQ but also the entropy AS = 0.7 k N flows from the heat 

reservoir to the gas during the expansion. Reversing this process, heat and entropy return again 

to the reservoir. This indicates a connection between heat and increase of entropy. The elementary 

calculation of AQ leads to AQ = 0.7 p V = 0.7 k X N X T. Thus at least in our special example 

we see: 

46

If a system receives the amount of heat AQ in a reversible process 

at temperature T the entropj, of the system increases by AS =AQf T. 


Thus heat is the form of energy transfer connected with entropy increase. This was to be expected 

since heat increases thermal motions and thereby decreases the information available about the 

system. 

The choice of the special factor 0.7 k in the definition of entropy is now motivated by the 

simple connection AS= AQ/T between entropy and heat which results thereby. We shall not 

attempt here to give a general proof for this relation [ 121 . 

THE FREE ENERGY 

A satisfactory description of all reversible processes taking place in isolated thermodynamic 

systems can now be given with the help of the entropy concept introduced above. In many 

practical problems - especially in chemistry and biology - thermodynamic systems are not 

isolated from their surroundings. In these cases it is necessary to consider the total thermodynamic 

system, composed of the original system and the laboratory. The total entropy ST 

increases during irreversible processes, while the total energy ET remains constant: 

AS, = AS+ AS, > 0, AE, = AE + AE, = 0. (Eq. 8) 

It is desirable to eliminate the variables concerning the laboratory from these equations. Since 

the laboratory can be considered a heat reservoir with approximately constant temperature we 

have TAS, = AEL = - AE. Inserting this into the first of the equations given above we obtain 

upon multiplication by T 

Because of the constancy of the temperature we can write this also in the form 

The quantity F defined by (Eq. 10) is the free energy of the thermodynamic system. Our result 

shows that the free energy decreases during thermodynamic processes taking place in a system in 

thermal contact with its surroundings. In thermal equilibrium the free energy becomes a 

minimum. 

These considerations can then be generalized to thermodynamic systems for which not only 

the temperature but also the pressure is fixed by their surroundings. In this case the free enthalpy 

G = E + p I' - TS decreases during irreversible processes 

AG = A (E + pV - TS)= AH - TAS < 0. (Eq. 11) 

The quantity AH, i.e. the change in enthalpy, is the heat given off to the surroundings during a 

chemical reaction or during other irreversible processes. This heat can also be negative (endothermic 

processes). 

These abstract considerations will be illustrated with some concrete examples in the following 

sections. 

47


WHY THE SKY DOES NOT COLLAPSE: THE HEIGHT OF THE ATMOSPHERE 

During the 17th century it was slowly recognized that we live on the bottom of a gigantic sea of 

air which extends even above the highest mountains. The question arises why this sea of air does 

not collapse and cover the earth in a thin layer with the density of liquid air. This density is of 

the same order of magnitude as that of water. A liquid air layer would therefore be only about 

10 m high, since a column of water of this height exerts the same pressure as the earth's atmosphere. 

The preceding discussion has shown that at a fixed temperature the equilibrium of a thermodynamic 

system is not determined by the minimum of the energy E but by the free energy 

F = E - TS. Which height H of the earth's atmosphere - we shaIl assume constant density for 

simplicity - leads to the minimal free energy at the temperature T = 300 K? 

In order to calculate H, we break the volume of a vertical column of air down into N = 2" 

sections, each with the 'minimal height' H, = 10 m. The average potential energy of an air 

molecule with the mass m in this column is 0.5 X 2" mg H, . This corresponds to an increase in 

energy of the molecule AE = (2"-' - 0.5) rng H, when compared to the imaginary liquid air 

layer. Similarly the entropy increases with H since we no longer know in which of the N = 2" 

sections of the air column the molecule will be found. The loss of information compared to the 

(idealized) initial state is thus n bit. The entropy therefore increases by 0.7 nk and the change 

in the free energy of the molecule becomes 

F(n) = (2"-l - 0.5) rng H, - 0.7 nk T. (Eq. 12) 

We now determine the minimum of the free energy as a function of n. This minimum is determined 

by F(n) F(n+l), since the derivative of F with respect to n vanishes. From this we obtain 

2"-' mgH, = 2"mgH, - 0.7 kT (Eq. 13) 

or with 2n H, = H 

This result can easily be interpreted. The average kinetic energy of the air molecules at the 

temperature T is 1.5 kT. The molecules can therefore rise up to a height H at which their potential 

energy rng H is equal to their kinetic energy. Inserting numerical values (k 10-23 

J K-l, T x 300 K, 

m = 3 X kg, g x 10 m/s2) leads to the correct order of magnitude of the height of earth's 

atmosphere, H 14 km [ 131. This corresponds to n X 10 and thus to the well-known fact that 

under normal (i.e. atmospheric) conditions the density of gases differs by a factor 21° 1000 

from the density of solids or liquids (figure 5). 

Our first example has illustrated some of the properties of the entropy and the free energy 

with the help of well-known facts. In the following examples we shall use the same mathematical 

framework to proceed slowly into more complicated and interesting problems [ 141. 

WHEN LIQUIDS LET OFF STEAM: MOLECULES IN SEARCH OF FREEDOM 

Every housewife knows that energy is needed for cooking. This energy is used basically for 

48


I l----i t--U-I 

I 1 , I I l l 1 

Figure 5. The scale height of the atmosphere. 

maintaining high temperatures, not for evaporating water, which has to be avoided rather carefully, 

since five times more energy is needed for evaporating than for heating water from 0 - 100°C. 

This energy is required to overcome the attractive forces between water molecules and for 

performing work against the air pressure. The heat of evaporation corresponds to this energy 

requirement. 

The higher energy of the molecules in the gaseous phase must correspond also to a higher value 

of the entropy since the free enthalpies of liquid and gas have to agree [ 151. 

Here A denotes the difference between gas and liquid and AH is the heat of evaporation, containing 

both the work against the molecular forces and against the external air pressure. 

In order to calculate AS we note that we lose ten bit of information when we go from a liquid 

to a gas, since the volume of a gas at normal temperature and pressure is roughly 1000 = 21° times 

the volumii of the corresponding liquid (figure 6). The entropy of each molecule increases therefore 

by AS = 7 k during evaporation. According to (Eq. 15) this leads to a heat of evaporation per 

molecule 

The ratio of (molecular) heat of evaporation and boiling temperature T should be a universal 

constant, 7 k. If the boiling temperature (at a pressure of 1 atmosphere) is not close to 300 K, 

but may be approximated by T = 300 X 2n K, where y1 is a positive or negative integer, the 

corresponding increase in volume during evaporation is given by 1000 X 2n x 2(10+n). This 

follows from the equation of state v = kT/p, since v, the volume per molecule, is proportional to 

the absolute temperature, if the pressure is kept fixed. Thus the entropy per molecule increases 

49


*- 

. . . . . I 

Figure 6. The loss of information per particle during evaporation is mainly due to the larger volume of the gaseous phase. Under 

normal conditions, the volumes of gas and liquid differ by a factor 1000 2”. 

during evaporation by 0.7k (1 O+n), as the following tables show. Table 3 gives the increase of 

entropy AS during evaporation under normal pressure as a function of the boiling temperature 

T. Table 4 compares this simple theoretical prediction with empirical data. The boiling temperatures 

considered vary by a factor IO3, the corresponding enthalpies even by 104. Despite this 

large range of variation, the ratio is almost constant (it changes only by a factor of 5). The 

agreement between theory and experiment - expressed by Trouton’s rule - is roughly 50 per 

cent [ 161. 

TABLE 3. Entropy increase during evaporation (theory) 

Boiling temperature T/K at p = 1 atmosphere 

4 

9 

19 

38 

75 

150 

3 00 

600 

1200 

2400 

4800 

Entropy increase AS per molecule 

2.8 k 

3.5 k 

4.2 k 

4.9 k 

5.6 k 

6.3 k 

7.0 k 

7.7 k 

8.4 k 

9.1 k 

9.8 k 

50


TABLE 4. Entropy increase during evaporation (experiment) 

Substance T AH AS' 

kT 

k 

(kelvin) 

(per molecule) 

AH 

TAS 

Helium 

Hydrogen 

Argon 

Methane 

Ethane 

Propane 

Butane 

Benzene 

Acetic acid 

Mercury 

Potassium 

Lead 

Iron 

Platinum 

4.27 

20.4 

87.6 

112 

185 

23 1 

273 

353 

391 

630 

1027 

2024 

3343 

4573 

2.37 

5.41 

8.55 

8.79 

9.56 

9.78 

9.87 

10.5 

7.29 

11.23 

9.08 

10.65 

12.75 

11.74 

2.8 

4.2 

5.8 

6.0 

6.4 

6.7 

6.9 

7.1 

7.2 

7.7 

8.2 

8.9 

9.4 

9.8 

0.85 

1.29 

1.47 

1.47 

1.49 

1.46 

1.43 

1.48 

1.01 

1.46 

1.1 1 

1.20 

1.36 

1.20 

1. See Table 3 (interpolated values) 

CRYSTALS WITH HOLES; OR NO (SOLID) BODY IS PERFECT 

We shall apply the principle of minimal free energy now to those systems which are usually considered 

to be the incarnation of perfect order, i.e. to crystals. The result is that this perfect order 

can be achieved only at zero absolute temperature. At finite temperatures imperfections, such as 

vacancies (Schottky defects) are unavoidable. 

In order to calculate the density of vacancies we consider a small segment of a two-dimensional 

crystal model containing 4 X 4 atoms or ions (figure 7). In a perfect crystal, all 16 lattice sides 

are occupied by an atom. In order to remove one of these atoms from the crystal lattice and to 

bring it to the surface, the energy E is needed, which is of the order of a few eV. The creation 

of a vacancy does, however, not only increase the energy, but also the entropy of the crystal, 

since the vacancy can be at any of the 24 = 16 lattice sides. This corresponds to a loss of information 

of 4 bit, i.e. an increase in entropy of AS = 0.7 X k X 4. 

Correspondingly the creation of two vacancies requires the energy 2~ [ 171 . Since these vacancies 

can be arranged in 16 X 15/2 = 120 27 different ways, the corresponding increase in entropy is 

AS = 0.7 k X 7. If we assign a free energy F = 0 to the ideal crystal (by an appropriate choice of 

the zero of energy), we obtain the free energy of the crystal as a function of the number of 

vacancies. The result is given in table 5. 

TABLE 5. Free energy of a crystal 

Number of vacancies E S F 

0 0 0 Fo = 0 

1 E 2.8 k F1 =E- 2.8 kT 

2 2E 4.9 k F2 = 2~ - 4.9 kT 

51


1. 0 0 01 

no vacancies 

one vacancy 

two vacancies four vacancies 2 

melting point: breakdown of 

long range order 

Figure 7. Vacancies in a crystal due to thermal motion. 

Figure 8 shows Fo, F1, F2 as functions of the temperature. The number of vacancies results from 

the condition that the free energy be a minimum for each given temperature. This leads to no 

vacancies up to a temperature To = ~/2.8 k, one vacancy for To < T < TI = e/2.1 k and more 

vacancies at higher temperature. 

The theoretical prediction of the number of vacancies as a function of temperature can be 

checked experimentally by measuring the density of the crystal. This density decreases at higher 

temperatures due to an increase in the number of vacancies. The vacancies contribute therefore 

to the thermal expansion. The main contribution to this expansion is due, however, to the 

increase of the lattice constant with temperature, a consequence of anharmonic lattice vibrations. 

These effects - vacancies and change in lattice constant - can be measured separately by 

determining the lattice constant as a function of temperature with the help of X-ray diffraction. 

The difference between the observed change in the lattice constant and the observed thermal 

expansion is the contribution of the vacancies shown in figure 9. 

TO ERR IS THERMAL: MOLECULES ARE LOUSY COPISTS 

In the introductory sections of this paper, we noted that the entropy of isolated thermal systems 

always increases, corresponding to a decrease in information about the system. The statement of 

the second law of thermodynamics seems to contradict the evolution of life, which has led to a 

52


\ 

Energy 2€\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ \ 

\ \ 

\ \ 

\' \ 

L\ \ 

\ \ 

\ \ 

\, 

\ ' 

' 1 

\ \ 

' \ 

h r 

&T 

Figure 8. The contribution of the vacancies to the free energy of a crystal is a function of the temperature. 

continuous increase of the information, contained in the genetic code. It had sometimes been 

argued that life contradicts the laws of thermodynamics and that a special quantity - entelechy 

- is necessary to characterize living organisms. It is remarkable that Ludwig Boltzmann had 

already speculated about this point and was firmly convinced that the laws of thermodynamics 

applied to living matter in the same way as to any other matter. 

Living systems are usually in thermal equilibrium with their surroundings. In contrast to the 

systems considered before, they are 'open systems' maintaining a continuous stream of matter 

and energy. This metabolism can maintain and even increase the information content of a system. 

In order to study how information is copied in living systems we consider a piece of RNA. 

This molecule plays an important role in the form of the transfer-RNA in every living cell and is 

one of the oldest information carrying molecules (figure 10). It is well-known that the RNA 

has the form of a phosphate-sugar-chain, each segment containing one of the four bases A(denine), 

U(racil), C(ytosine) and G(uanine). Hydrogen bonds can connect the base pairs A and U on the 

one hand and G and C on the other hand, since only these fit one another geometrically. 

If one inserts these strands of RNA into a solution containing free monomers, i.e. single chain 

segments with bases A, U, G and C, these segments arrange themselves into a complementary 

strand of the original molecule due to the formation of hydrogen bonds between corresponding 

base pairs (figure 10). After polymerization, i.e. formation of covalent bonds between adjacent 

segments, this second strand can then be separated from the original RNA and can itself become 

53


m 

0 

19 

I 18 

c- 17 

rc 

1 6 

LI1 

e 15 

C 

' 1 4 

\ 

q m '3 

L 

0 12 

d1-I 1 1 

Aluminium 

1 0 

400 450 500 550 600 650 

Te m p e r at u re/OC 

Figure 9. The contribution of thevacancies to the thermal expansion. This contribution is measured by determining the difference 

between the thermal expansion nL/L and the relative change of the lattice parameter aula. 

Complementary Array of Monomers ( before Polymerisation to 

a "Mirror" Strand) 

Original RNA- Strand 

Figure 10. When a RNA-molecule is copied without the help of enzymes, a number of 'thermal errors' will occur. 

54


the starting point of a new copying process. In this process, an identical copy of the original 

molecule results. 

In order to preserve the genetic information it is essential that errors in copying are duly 

avoided. There is a limit,however, to the fidelity of the copying process due to the thermal 

motion of the molecules. Therefore there wil be a corresponding limit in the maximal length 

of the molecule that can be duplicated essentially free of errors. For molecules longer than this 

limit,the probability for the occurrence of copying errors wil be overwhelming. In order to 

calculate this critical length we repeat the considerations of the previous section. The vacancy 

in a crystal corresponds here to a copying error. Since no hydrogen bonds wil be formed in this 

case, an energy increase E wil result. Energy and entropy again fight for the privilege to minimize 

the free energy. If the RNA-molecule consists of N = 2" bases, we obtain for the free energy 

of a copy containing zero or one error: 

The critical length of the molecule is given by F1 = 0, i.e. by E = 0.7 y1 k T. The corresponding 

length of the molecule is thus 

N= 2" = 2 (elO.7 kT). 

(Eq. 18) 

Since the energy of a hydrogen bond is roughly 0.1 eV, we have E 0.2 eV or 0.3 eV. From 

this we obtain N x 214 lo4. Since the critical length depends exponentially on E an exact 

estimate is rather difficult. 

Our result shows that the transfer-RNA which contains about seventy base pairs and is likely 

to be one of the oldest information carrying molecules, could reduplicate without difficulty in 

an error-free way during the initial phases of the evolution. In contrast to this, the DNA-molecules 

of microbes, containing 1 O6 base pairs each, can reduplicate in an accurate manner only with the 

help of enzymes. 

CONCLUSION 

The preceding examples have shown that numerous interesting properties of thermodynamic 

systems can be described without the help of complicated mathematical methods by using the 

information theory approach to thermodynamics outlined above. All examples considered here 

are based on a single equation which is used in various versions and interpretations, i.e. the free 

energy of a system consisting of 2" pieces. Without difficulty, the number of examples considered 

here can be increased and problems such as adiabatic demagnetization, the entropy of thermal 

radiation etc. can be considered. In many of these problems, a quantitative calculation will not 

be needed and a qualitative insight into the behaviour of the system, based on the information 

theory approach to thermodynamics, can be of great pedagogical value. 

55


REFERENCES 

1. The entropy at zero absolute temperature is usually assumed to be zero according to the third law of thermodynamics. 

This law is however not universally valid and is not correct for all materials with degenerate 

ground states, such as ice. The zero point energy can be determined experimentally by using (l), since the 

entropies in the gaseous phase can be calculated from a universal expression. 

2. SHANNON, C.E.; WEAVER, W. A Mathematical Theory of Communication. Urbana, Ill., University of 

Illinois Press, 1949. 

WIENER, N. Cybernetics. Cambridge, Mass., MIT Press, 1961. 

3. BRILLOUIN, L. La vie, la matigre et la thkorie de l’lnformation. Paris, Albin-Michel, 1959. 

Science and Information Theory. 2nd ed., New York, Academic Press 1956, 1962. 

Scientific Uncertainty and Information. New York, Academic Press, 1964. 

WOODWARD, P. Probability and Information Theory with Applications to Radar. London, Pergamon, 1953. 

PIERCE, J.; CUTLER, C. Interplanetary Communications. New York, Academic Press, 1959. 

FEINSTEIN, A. Foundations of Information Theory. New York, McGraw-Hill, 1958. 

SCHULTZE, E. Einfiihrung in die mathematischen Grundlagen der Informationstheorie. Lecture Notes in 

Operational Research and Mathematical Economics. Berlin, Springer, 1969. 

4. A treatment of the more general case with events of unequal probability is given in all the references mentioned 

above. 

5. See e.g. PIERCE, J.R., Symbols, Signals and Noise. New York, Harper, 1961. 

6. See e.g. STRYER, Lubert, Biochemistry San Francisco, Calif., Freeman, 1975. 

7. See e.g. MEYER-EPPLER , W. Grundlagen undAnwendungen der Informationstheorie. 2nd ed., Berlin, Springer, 

1969. 

8. See e.g. SEXL, R.U. ‘Irreversible Prozesse’,Physik und Didaktik, Vol. 1, 1980, pp. 1-14. 

9. If one tries to prove this fact mathematically from the equations of motion of the molecules it turns out 

that the entropy is constant in time for all strictly closed systems with a finite number of particles. Real 

systems are, however, never strictly closed but interact on their surface with their surroundings, SO that the 

constancy of the entropy cannot be derived for such systems. Even in completely isolated systems where no 

information is lost in the course of time this information changes its meaning completely. After sufficient 

time the information is no longer contained in the distribution of the various particles in configuration or 

momentum space but in the correlation of all particles. The distance between two initially distinct states in 

phase space becomes unmeasurably small in the course of time. This distance is even completely meaningless 

from the point of view of physics if the number of particles N exceeds the order of magnitude 100. The 

reason for this is that N enters the distance between various states in phase space exponentially and the range 

of all magnitudes known to physics extends at most over 10’Oo. One therefore would have to measure the 

position and momentum of all particles for macroscopic systems at the same time with the precision loi“ 

(N is the number of particles) in order to distinguish initially different states after sufficient time. Any 

arbitrarily small disturbance of the system by the surroundings leads to a complete loss of the initial information. 

10. The connection between entropy and missing information was recognized for the first time by Ludwig 

Boltzmann, about 70 years before the creation of the information theory by Shannon and Wiener. Boltzmann’s 

famous equation S = k In W uses natural logarithms for the description of information and not the 

binary logarithms customary in information theory. The quantity W, Boltzmann’s thermodynamic probability, 

corresponds to our symbol N, i.e. to the number of all microscopic configurations of the system. 

11. CLAUSIUS, R. Fur die Anwendung bequeme Form der Hauptgleichung der mechanischen Warmetheorie. 

PoggendorfjsAnnalen, Vol. 125,1865,~. 390. 

12. See all standard textbooks of thermodynamics, e.g. REIF, F. Fundamentals of statisticaland thermal physics. 

New York. McGraw-Hill, 1965. 

13. Here we refer to the height of the troposphere, which has - in contrast to the higher layers of the atmosphere 

- a rather sharp upper limit, the tropopause. 

14. Taking into account the possibility that the various sectionsconsidered here do not necessarily have to contain 

the same number of particles one can decrease the free energy even further. In equilibrium one obtains a 

density distribution p(h) = p(0) exp(-F;h ). At the height h = H = 1.4kT/mg the density decreases to 

exp(-1.4) e 1/4 of the surface value. 

56


15. If the free enthalpy of one of the two phases would be lower than in the other phase the absolute minimum 

of the free enthalpy would be completely on the side of this phase and the two phases would not coexist. 

16. The experimental values for the increase in entropy - with the exception of helium - are larger than the 

theoretical values calculated from the information loss during evaporation. Since the liquid and its steam 

have the same temperature at the boiling point, the momentum distribution should agree according to the 

equipartition theorem. Certain degrees of freedom, e.g. rotation of the molecules can be ‘frozen’ in the liquid, 

however. This leads to a possible increase of the thermal motion, of the angular momentum and similar 

quantities in the gaseous phase as compared to the liquid and thus to a further increase in entropy. This 

increase is especially large for polar, non-linear molecules. This is the reason for the large heat of evaporation 

of water, which is 80 per cent higher than the simple theoretical value calculated here. 

The reason for the exceptional properties of helium is the fact that the density of this liquid is much lower 

than the size of the molecules would indicate. Due to quantum fluctuations, the average distance between 

particles is 0.45 nm rather than 0.1 nm. The increase in volume during evaporation and the corresponding 

increase in entropy is therefore much lower than for standard liquids. 

17. Close to the melting point, a high concentration of vacancies occurs. In this case, the creation of additional 

vacancies requires an energy lower than E. 

57


Energy and energy degradation as complementary aspects 

of energy processes and a stepwise introduction to the 

concept of energy 

H. SCHLICHTING. 

One reflection of the permanent public interest in problems concerning energy is the renaissance 

of interest in the concept of energy in science teaching. New school books devote more space 

to energy than their predecessors and the number of articles about energy in journals of science 

teaching has increased. 

However, the influence of the real problems of the scientific-technical world on the content of 

science teaching is one-sided; there is little appreciation that the investigation of energy in school 

would contribute to a better understanding of the world’s energy problems. 

In our opinion this is largely due to two factors: first, the energy concept is generally taught 

independently of its significance for everyday life, and, second, the topic of energy is reduced to 

just one aspect - conservation. The consumption or down-grading aspect, although much more 

important in everyday life, is given scant attention. 

The first of these two factors refers to the current practice in school courses. Apart from a few 

exceptions, mainly in English-speaking countries (e.g. Nuffield [ 1 1 energy is derived from 

other mechanical quantities according to the scheme: force + work += energy. This implies that 

the understanding of energy is intended to follow from an understanding of combinations of 

quantities which are, by themselves, very difficult concepts. This detour via other quantities 

renounces not only the possibility of starting from a common-sense understanding of energy 

based on many familiar phenomena (see e.g. Schlichting and Backhaus [ 21 ) but even detracts 

from any common-sense understanding that may develop. A confusion, injurious to understanding, 

of two ideas about energy may result. Moreover, this academic treatment leads to 

another conflict with everyday experience: energy is introduced as a conserved quantity and 

pupils are taught that it may neither be created nor destroyed. In a physics lesson taught by the 

author, a pupil asking how the existence of an energy crisis fits with the conservation of energy, 

alludes to those experiences which have taken energy into the focus of social-political interest: 

(1) Man’s energy supply has become uncertain because (2) the conventional energy resources are 

being steadily depleted. (3) Alternative resources are being sought and, (4) on all sides, people 

are asked to save energy and to be ‘energy conscious’. 

Furthermore, the experience of pupils in which the fuel tanks of cars and trucks become 

58

Energy degradation 

empty and in which their parents have to pay more for electrical energy and gas as each month 

goes by do not exactly exclude the possibility of ‘energy consumption’. In order to avoid the 

discrepancy between what the pupil perceives as reality and the scientific description of reality, 

it must be stressed that the words ‘consumption’ and ‘conservation’ as applied to energy do not 

imply a contradiction when used in discussions on energy. They express complementary aspects 

of the same experience. 

ENERGY CONSUMPTION AS DEGRADATION OF ENERGY 

From the physical point of view, this procedure is fully justified. It reflects the fact that these 

two aspects correspond to the physical concepts of ‘energy’ and ‘entropy’. These are as closely 

related to each other as are the corresponding common-sense concepts of ‘energy’ and ‘energy 

consump tion’. 

To talk about ‘energy consumption’ is in accord with the use of the word ‘consumption’ in 

other fields. For instance, in a household, water is used up (permanently) for washing, cleaning, 

flushing the water closet etc. But, obviously, the water is not annihilated; it is conserved quantitatively. 

This may even appear in the fee charged for the disposal of the spoiled (waste) water and 

sometimes calculated from the quantity of water discharged into the sewer. Water drained off 

into the sewage system is used up in the sense that it is impossible to re-use it as it is. Similarly, 

a motor-car is ‘used up’ because, in the course of time, it depreciates - it gets more and more 

defective and finally ends its life at the scrap yard. 

Such examples show that the words ‘to conserve’ or ‘to use up’ are not normally applied in 

the sense of a destruction of quantity but of a change in quality. Because of the impossibility 

(or, at best, ‘limited possibility’) of re-using the above mentioned things for their original purpose, 

the change in quality is a loss of value, a degradation. 

As the following examples show, the expressions ‘energy consumption’, ‘energy loss’, and 

‘to use up energy’ may be applied in the same sense. 

Example I Hot water, exposed to cooler surroundings, cools to the temperature of those 

surroundings. This process involves a degradation of energy in that the energy of the water, 

originally supplied, perhaps, by an immersion heater, has disappeared. It has been transferred 

irrevocably to the surroundings. There, it is good for nothing. 

Example 2 The water of a waterfall, falling through a height, may be used to drive turbines 

and, by means of a generator, produce electrical energy. Without turbines, the potential energy 

of the water would have been transformed into thermal energy and shared between the water 

and the surroundings. The energy has been degraded.’ 

Example 3 A motor-car uses up the chemical energy contained in petrol. Except during 

acceleration, this energy is used to overcome air and rolling resistance, and it is dissipated. It is 

degraded because it may not be re-used. 

These few examples may suffice to show: 

Energetic processes are always accompanied by a degradation of energy. 

This finally transforms the energy into a form of which no use can be made. (1) 

1. This example shows how difficult it may be to detect energy conservation in the phenomena observed. Here the effects of the 

turning turbines which are, in turn, responsible for other obvious effects are much more striking than the almost imperceptible 

thermal effect. 

59


This statement contains the qualitative content of the second law of thermodynamics. According 

to Brillouin [3, p.3221, ‘the inanimate world, governed by physics and chemistry, obeys a 

natural law of degradation, of loss of value. This law sums up the essentials of thermodynamics, 

but the notion of value remains linked to. . . energy. Physics has not been able to (and probably 

cannot) separate these two entities.’ 

THE QUALITATIVE CONCEPT OF ENERGY DEGRADATION 

~ 

In order to compare different processes with respect to their different degrees of degradation, the 

concept itself must be made more precise. This requires us to free the valuation of energetic 

processes from their subjective attributes. This cannot be done without introducing a certain 

artificiality in explanation which must be accepted as the price we pay for a gain in .precision. 

As may be concluded from the examples given above, degradation consists (objectively) of a 

kind of irrevocable change; one which cannot be undone. The cooling of the hot water in a cold 

room is no more reversible than is the transformation of the kinetic energy of a motor-car into 

thermal energy of its surr0undings.l 

To object that the mechanical energy of the motor-car could be recovered by the consumption 

of additional chemical energy of petrol and that the cooled water can be re-heated is invalid. For, 

in addition to restoring the original states, there is an increase in the thermal energy of the 

surroundings and an equal decrease in the chemical energy of the petrol in the first case and a 

further input of electrical energy in the second case. 

A process is accompanied by a degradation of energy if it cannot be reversed 

without causing an additional change in its surroundings. (2) 

Such irreversible, energy-degrading processes which run spontaneously in a certain, natural 

direction we shall call ‘spontaneous processes’. 

Extending this consideration to composite processes, proposition (2) even holds in situations 

where a part of a whole process consists of a process running opposite to its natural direction 

(e.g. the objection already referred to). 

Reversing the ‘cooling of water’, i.e. the ‘heating of water’ combined with the ‘consumption 

of electrical energy’ considered as a whole, is a process which runs down without causing any 

additional change in the surroundings and, therefore, gives rise of an energy degradation. 

Thus although the spontaneous process ‘cooling of water’ is reversed and therefore accompanied 

by an upgrading of energy, it may take place because simultaneously, another process, ‘the consumption 

of electrical energy’ is running down providing for an even larger degradation. Overall, 

a small degradation results. 

Or, more generally: 

The energy degradation due to a spontaneous process a is greater than that due to a 

second spontaneous process /3 if a can drive /3 backwards (i.e. in the opposite direction 

to the natural one). This implies that the degradation of energy associated with a 

exceeds the upgrading of energy due to the reversed process 0, (3) 

1. In the following pages, the processes which are fully described as ‘cooling of a hot system by transferring energy to the 

sunoundings’ and ‘braking a moving system by transferring energy to the surroundings’ are sometimes abbreviated to ‘cooling’ 

and ‘braking’. 

60


1 

The heating of water by, for example, an immersion heater may be thought of as the reversal of 

the process ‘cooling of the hot water by transferring energy to the surroundings’ by the application 

of the process ‘dissipation of electrical energy to the surroundings’. The upgrading of energy 

associated with the transfer of energy from the surroundings to the hot water is compensated 

by the degradation of electrical energy. The net effect corresponds to what is observed, namely 

the transfer of electrical energy to the water raising its temperature.’ 

Our concept of degradation of energy implies that the spontaneous processes may run without 

affecting anything else. In that case, the energy degradation is a maximum. Alternatively, spontaneous 

processes may be used to reverse other processes which have already run down spontaneously. 

In this case, the degradation is reduced by the upgrading which is effected. 

To give a concrete example, instead of using an immersion heater to increase the thermal 

energy of a lake which would not perceptibly change the temperature of the water, we could 

increase the temperature of a pot of water considerably with the same electrical energy. 

A spontaneous process combined with an energy degradation may 

I 

drive another process combined with the upgrading of energy. (4) 

From this point of view, the human use of energy is not energy destruction but the application 

of certain energy transformations (e.g. the burning of oil or the passage of an electric current) to 

drive in reverse certain processes which humans regard as important. In other words, in using up 

energy these processes may be prepared to run spontaneously again and again producing heat, 

motion, light, sound and various other forms of energy. 

A first impression of the power of the concept developed so far may be obtained by considering 

the processes involved in the absorption and emission of sunlight by the earth. We shall 

demonstrate how events which, analysed by energetic arguments alone, turn out to be relatively 

complex and even inexplicable, may be unfolded in a simple way by applying the concept of 

energy value. 

On the degradation of sunlight 

We may interpret the solar energetic events to which man owes nearly all his available energy in 

terms of the value of the energy as follows. Consider the Sun as a huge energy radiator. A part 

of that radiation is absorbed by the Earth and the same amount is reemitted into space. If one 

were limited to the principle of energy conservation, this balance would be all one could describe. 

However, the radiation received from the Sun is not only absorbed and re-emitted; it is degraded. 

Arriving at the Earth with a temperature of 5700K (for temperature of radiation see e.g. 

Schlichting et al [41) the re-radiated energy leaves at the Earth’s temperature of about 290K. 

This temperature change corresponds to a change in the frequency of the radiation. As visible 

light arrives at the Earth, invisible infra-red radiation leaves. If the dissipation of the solar radiation 

is the only process involved, this enormous cooling of the radiation represents a very large 

down-grading of the energy. As an example approximating to this, consider the absorption and 

the re-emission of energy from, say, the Sahara desert. Elsewhere, and more normally, this 

energy degrading process goes on in a very roundabout way, driving other spontaneous processes, 

already run down, in reverse. 

1. Although it changes nothing, the participation of the surroundings has to be introduced if we are to conceive the whole 

process as a combination of one process driving another one backwards. This is fundamental to our concept of value. 

61


The absorption of ‘hot’ solar radiation by the green leaves of plants (photosynthesis) may be 

regarded as a first step in a long, roundabout path which eventually leads to the release of the 

energy to space as invisible low temperature radiation. In this first step, the spontaneous process 

of decay of biological material is reversed. Left to itself, and deprived of sunlight, biomatter 

decays, absorbs oxygen, produces carbon dioxide and water and emits heat to its surroundings; 

photosynthesis reverses the process. Using sunlight, biomatter is synthesized from carbon dioxide 

and water with the emission of oxygen. 

A second step on this roundabout path may be the utilization (i.e., burning) of fossil fuels to 

generate (e.g., by means of thermal power plants) mechanical and electrical energy. Having been 

buried under massive layers of rock for many millions of years, huge masses of biomatter have 

been prevented from decaying. In a power plant, the energy degradation which might have been 

dissipated in the process of decay is harnessed to reverse important processes (such as the dissipation 

of electrical and mechanical energy) and hence upgrade energy. The overall degradation is 

thus reduced. 

Further steps may include (i) the application of the dissipation of the electrical energy to drive 

in reverse processes which are important for human purposes and (ii) the use of biomatter as 

food, making possible human and animal life in its various manifestations. 

The driving of the natural water cycle provides another example of a roundabout path of 

great importance. In condensing and then falling from the clouds as rain or snow, water transforms 

huge quantities of mechanical energy into heat. It is lifted back to high altitude by the 

reverse process of evaporation which is driven by sunlight. Condensing yet again to form clouds, 

water may once more fall back to Earth and so on. Under appropriate conditions, the precipitation 

may accumulate in the hills,form rivers and then, instead of dissipating the rest of its mechanical 

energy by flowing to the sea, it may be harnessed to drive hydroelectric power stations. 

A further example of a potentially useful roundabout path lies in the driving backwards of 

spontaneous temperature balancing processes in the atmosphere, producing further temperature 

differences. The balancing of those differences through the movement of air as wind may then be 

used to reverse other spontaneous processes useful for human affairs. 

These few examples may suffice to indicate how, in the end, these and similar events may be 

explained by the possibility that spontaneous processes, when running down, may pass along 

roundabout paths and drive in reverse other spontaneous processes of importance to mankind. 

By the overall process of energy degradation, the absorption of visible sunlight and the emission 

of invisible infra-red radiation, many processes important for life on Earth are driven through 

cycles; running spontaneously in one direction, they are harnessed to run up in the other direction. 

Energetically speaking, we may say that energy degradation may cause energy to be upgraded. 

visible sunlight 

photosynthesis 

Figure 1. One of the life cycles on Earth driven by the dissipation of sunlight (after Bent [5]). 

62


Therefore ‘the general struggle for life of all creatures is not a struggle for raw material. . . 

nor for energy, which is, unfortunately, unchangeable, contained in every body, but a struggle 

for entropy [we would say: for energy upgrading] which becomes available by the transfer of 

energy from the hot Sun to the cold Earth’ (Boltzmann, [ 6, p.401). 

On the value of different energy forms 

For understanding and estimating most of the energy problems in the world today the scheme 

of energy degradation described above may be simplified by abstaining from the processes and 

concentrating attention on the different forms of energy involved. By assigning a certain value 

to each form of energy, we can at least give a rough estimate of the events in the spirit of our 

degradation concept. 

For instance, electrical energy may be regarded as being more valuable than heat. We can see 

that this is so by noting that, while it is not possible to drive (in any simple way) a television set 

or a vacuum cleaner with heat, heat at the temperature we need may readily be produced by 

electrical energy. Electrical energy is universally applicable. In principle, it may be used to 

reverse other processes (although the opposite does not hold). A definite quantity of electrical 

energy may be used to drive in reverse another process which involves the same quantity of 

energy in a different form. This is also true of mechanical energy; so we may assign the same 

high value or grade to both electrical and mechanical energy. 

Generally speaking, the following sequence provides a hierarchical scheme which may be 

used in the qualitative examination of energetic events: 

High grade or value 

Mechanical, electrical energy 

L 4 

Chemical energy 

4 

Thermal energy (0 ) 

3- 

Thermal energy (0,) 

Low grade or value (5) 

This assumes that mechanical and electrical energies are the most valuable whilst thermal energy 

is lessvaluable. More precisely, the value of the thermal energy (heat) depends on the temperature 

(e) at which it appears or is transferred; the higher the temperature, the more valuable is the 

energy. This will be considered in more detail below. Here it may suffice to remark that a body at 

a high temperature can be used to heat a cold body, (i.e. can reverse its cooling down) while the 

opposite is impossible. In practice, the thermal energy of the (coldest) surroundings has no value, 

because nothing can be driven in reverse by this energy. 

Chemical energy holds a middle place in the value sequence for, in chemical processes, since a 

part of the energy is emitted as heat at a finite temperature, the chemical energy is not as valuable 

as electrical and mechanical energies. But, in the domain of normal temperatures, chemical 

energy is generally more valuable than thermal energy. 

63


It should be noted that this simple concept of value is largely in accordance with the usefulness 

of the energy forms to man: the higher the corresponding temperature, the more useful is 

the thermal energy. Electrical and mechanical energy are good for nearly everything - including 

the production of thermal energy at arbitrarily high temperatures. 

Examples 

A heat engine (HE) may be considered as a device which produces high value electrical or 

mechanical energy from low value thermal energy. To accord with the principle of energy 

degradation stated above, this can only be achieved if one part of the thermal energy is upgraded 

to electrical energy while another part is degraded into thermal energy at a lower temperature 

(usually the temperature of the surroundings). This explains the necessity for a cold reservoir 

in a heat engine. The quantity of energy transferred to the cold reservoir must be large enough 

to ensure that the corresponding degradation exceeds the revaluation involved in upgrading the 

thermal energy into the electrical form.’ 

Further qualitative conclusions may be drawn from this presentation without the need for 

special thermodynamic knowledge (of, e.g., the Carnot cycle). If we define the efficiency qHE of 

the heat engine as the ratio of the energy in the form desired (here, electrical) to the energy in 

the form supplied (here, thermal at a relatively high temperature), one realizes that must 

be less than unity, because the electrical energy developed is less than the thermal energy supplied. 

Moreover, one may conclude that the efficiency depends on the temperatures of the ‘hot’ 

reservoir (e.g. steam) and the ‘cold’ reservoir (e.g. condenser): the higher the temperature of the 

former and the lower the temperature of the latter the greater the efficiency which is theoretically 

possible. For, if the temperature of the hot reservoir is high, i.e. the thermal energy has 

already a high value, only a small upgrading is needed to produce mechanical energy. Applying 

proposition (I), only a small amount of energy has to be degraded. Moreover, the lower the 

temperature of the cold reservoir, the smaller this amount becomes because the effect of degrading 

a given quantity of energy is the greater the lower the temperature of the cold reservoir at 

which this energy is absorbed. 

In apparent contradiction to experience, a heat pump (HP) succeeds in shifting the thermal 

energy of cool surroundings to the higher temperatures able to warm a room. This difficult idea 

turns out to be simple to understand if considered in the light of the value of the energy involved. 

To shift thermal energy to a higher temperature the heat pump uses, say, electrical energy (i.e. 

high value energy). The upgrading required for the production of the temperature difference is 

compensated by the downgrading of the electrical energy provided. In fact, the quantity of 

upgraded thermal energy is closely related to the quantity of electrical (or mechanical) energy 

driving the pump: the higher the temperature shift and the greater the quantity of energy 

upgraded, the more electrical (or mechanical) energy has to be supplied. If we consider the 

efficiency of the process qHp, we see that qHp > 1, because the desired energy (here thermal 

energy to heat a room) is greater than the energy supplied to work the pump. As we have seen, 

the smaller the temperature shift required, the greater the efficiency which is theoretically 

possible. In order to save valuable electrical energy, the temperature to be reached in the heated 

room should be as low as possible and the temperature of the surroundings from which energy is 

drawn should be as high as possible. This may be achieved by using ground water rather than the 

air, for example. 

1. Here we make the obvious assumption that the degradation increases with the quantity of degraded energy. This is explained 

below. 

64


Finally, we note that the description of the life cycles (see above) driven by the dissipation of 

sunlight could be further simplified by assigning a value to the different energy forms instead of 

considering the capabilities of some processes to reverse other processes. For example, photosynthesis 

could be described, by analogy with the heat engine, as upgrading heat radiation to 

chemical energy to be stored in plants. The emission of heat to the surroundings by the plants 

(through evaporation etc.) may be considered as the corresponding energy degradation, necessary 

to compensate that upgrading. (The far-reaching analogy between the green leaf and a heat engine 

has been worked out by Schlichting et a1 [ 41 .) 

QUANTITATIVE ASPECTS OF ENERGY DEGRADATION (ENTROPY) 

On the connection be tween energy degradation and entropy 

The explanations above have shown that the qualitative concept of degradation is able to describe 

a multitude of phenomena from a single viewpoint and to contribute to a deeper understanding 

of energy problems. 

If, in addition, one wishes to estimate certain degradations quantitatively and to make 

measurements, it is necessary to quantify the concept. 

As a description of an appropriate measuring procedure does not contribute significantly new 

aspects, we shall confine ourselves to a rough sketch showing how the qualitative aspects of 

degradation may be related in an intuitive way to the quantitative concept of entropy (see 

Backhaus et al, [7, 81 ). The starting point for the quantification is the fact, described above, that 

the overall degradation is the smaller the-more strongly one spontaneous process is harnessed 

to drive another backwards. 

To be more precise, we must first demonstrate the fact implicit in the notion of degradation 

that the energy degradation increases with increasing energy consumption. If two otherwise 

equal processes differ in the quantity of dissipated energy (e.g. the cooling of two different 

masses of water from, say, 100°C to the temperature of the surroundings), the degradation of 

energy increases as the quantity of dissipated energy increases. 

If we assume that energy degradations are additive we may state: 

The energy degradation of a process is proportional to 

the energy degraded. (6) 

On the other hand, the different temperatures of the systems involved in the process have to 

be taken into account. Considering, for example, the ‘cooling of hot water in cold surroundings’, 

it is obvious that the degradation depends intimately on the temperature 8 of the water and the 

temperature O2 (< 8 ) of the surroundings; and we may write 

This may be shown as follows: 

(a) The higher the temperature 8 of the hot water and 

(b) the lower the temperature O2 of the surroundings 

the greater the down-grading of the energy. (7) 

(a) Let a be the process ‘cooling down of a body at temperature 8 to temperature O2 by the 

transfer of energy to the surroundings’. The process 0 differs from a only in that the body has a 

temperature 8 < 8 1. a may be used to drive 0 in reverse, As a result of cooling one body from 

65


8 to O2 the other body is heated from O2 to 8 ;(< 8 ). 

In general a combination of heat engine and heat pump are required to achieve the reversing 

process: heat conduction between the two bodies works only in special cases. 

(b) The process Y differs from a only in that the surroundings are at a temperature 8 2' , which 

is greater than 02, i.e. by a heat conduction process between 8; and 02. Therefore the energy 

degradation produced by a! is equal to the energy degradation due to 'd and this heat conduction 

process; this means that it is greater than that of 'd alone. 

The qualitative concept of energy degradation is based on a consideration of processes. 

Although, in most of the examples considered, our interest has been focused either on the 

energy emission (e.g. the cooling of hot water) or on the energy absorption of a system (e.g. 

the melting of ice in a warm room), the degradation always referred to the full process of energy 

exchange between at least two systems. If one is interested in making more precise statements 

(e.g. about the behaviour of just one system involved in the process) the concept of degradation 

already developedis too crude. This is the price we pay for doing without thermodynamic notions 

and reasoning; for, in other words, simplicity. 

The quantitative concept has to be able to describe the behaviour corresponding to degradation 

of energy within a part of a process (e.g. the emission of energy only) and express it in terms of 

one of the systems involved as well as the properties already described by the qualitative concept. 

As already indicated, this is achieved by introducing the entropy change AS'. 

In the usual phenomenological definition 

Qrev 

AS=- T 

where Qrev is the reversibly exchanged heat and T the absolute temperature (see e.g. Zemansky 

191 ). 

It can be seen that entropy change is proportional to the energy exchange and inversely 

proportional to the Kelvin temperature. 

The following examples wil show how the energy degradation of a process can be further 

subdivided in terms of entropy and be related to single systems. 

Some examples 

The cooling of hot water 

First, we wil consider the simple example of hot water cooling in colder surroundings. 

This process is associated with energy degradation and in terms of (8) we have 

AS20 (9) 

(This is the quantitative version of the principle (1) of spontaneous energy degradation; it 

is the Second Law of Thermodynamics. The equality sign holds for the ideal limiting case in 

1. This is not the only possibility; but it does permit a connection with standard thermodynamics. A more direct quantitative 

development such as an application of the concept of degradation to systems would lead to a somewhat different quantity, which 

would assign a value proportional to the exchanged quantity even if only mechanical and electrical energy were involved. 

66


which the downgrading of a spontaneous process CY is equal to the upgrading of the process p 

reversed by a, i.e. in which CY and p may drive each other backwards.) 

If we subdivide the process into (a) the emission of heat Q1 at temperature Tl of the system 

‘hot water’ and (b) the absorption of heat Q, at temperature T2 of the system ‘surroundings’, 

we get two contributions to the overall entropy change AS. The system ‘hot water’ suffers an 

entropy decrease of* 

The system ‘surroundings’ acquires an entropy increase of 

The overall entropy change AS, which describes the energy degradation amounts to 

in accordance with (9). 

Figure 2. Diagrammatic representation of a heat engine. According to our sign convention Q, > 0; W, Q, < 0. 

We now wish to describe two examples which are characterized by energy transformations 

from one form to another. In order to get quantitative expressions, we must make use of the 

quantitative version of the principle of conservation of energy - the so-called First Law of 

* These simple expressions are approximations. They are strictly valid only for reservoirs, where the temperature changes which 

are connected with heat transfers may be neglected. 

** In accordance with most German-language textbooks, the emission of energy from a system is regarded as negative and the 

absorption is regarded as positive with respect to the system. 

Editor’s note: 

In English-speaking countries, it has been the custom to adopt an alternative sign convention according to which 

the First Law of Thermodynamics is written b? = Q - W and in which both the energy absorbed and the work (energy) put out 

are positive in sign. 

67


Thermodynamics. The well known expression’ 

AE=W+Q (13) 

means that an energy exchange AE of a system may be realised by absorption (counted positively) 

and emission (counted negatively) of mechanical (electrical etc.) energy (transmitted in the form 

of work) or of heat2. 

As already discussed qualitatively, (page 64) a heat engine (HE) transforms, in principle, a 

quantity of heat Ql given out by a hot reservoir at temperature Ti partly into mechanical work 

(energy) W and partly into heat Q, given to a cold reservoir at temperature T2 (< TI 1. 

See figure 2. 

The amount of heat Q2 given to the cool reservoir has to be large enough for the corresponding 

degradation of the energy to compensate for the upgrading associated with the transformation 

of heat into mechanical work. Speaking quantitatively3 

Qi 

The efficiency vHE which is defined as the ratio of the desired work -W and the heat supplied 

may be determined by condition (1 5) together with (14): 

From this we conclude that heat may be transformed completely into mechanical (electrical, 

etc.) work only at infinitely high temperatures. Conversely, mechanical work may be conceived 

of as heat transferred at infinitely high temperatures (see Boltzmann [ 61 ). The corresponding 

entropy change is then AS = 0 and there would be no degradation. This is in accordance with 

our qualitative estimate (page 63) that the mechanical (or electrical) energy has to be regarded 

as the most valuable form .of energy. In practice the production of arbitrarily high temperatures 

by means of electrical or mechanical work is restricted only by technical considerations. 

1. See Editor’s note at the foot of page 67. 

2. The problem of the exchange of chemical energy will be omitted here. 

3. Relative to the system HE, Ql > 0 and Q2, W < 0; the entropy change a(;3 of the HE is zero because the HE is working 

cyclically. 

68

The heat pump 


Finally, we wish to consider the application of the concept of entropy to the heat pump (see 

figure 3). As has been shown above (page 64) a heat pump (HP) is a device with which it is 

possible to harness the process of the degradation of high value energy (e.g. electrical energy) 

to shift thermal energy (e.g. of the surroundings at temperature T2) to a higher temperature 

T1. On condition that the overall devaluation is kept to a minimum, the quantity of electrical 

energy W necessary to 'produce' a desired quantity of heat Q, (which is a measure of the efficiency 

qHp) can be calculated as follows: 

The entropy decrease of the surroundings at temperature T2 

has to be compensated by the entropy increase 

Q2 

AS2 = -- ,(Q2 > 0) 

T2 

of the room heating, such that 

Qi + 

AS=ASl +AS2 7-- Qi+W >o 

Tl T2 

The efficiency is, therefore, 

I 

TI 

1 

w 

I 

T2 I 

Figure 3. Diagrammatic representation of a heat pump. 

69


SUMMARY 

Starting from the observation that there is a discrepancy between the scientific concept of energy 

conservation and the popular notion of energy consumption, it is shown that, contrary to the 

usual presentations in textbooks where energy is restricted to its quantitative aspect, energy 

possesses an aspect of value. As this aspect is important for a clear understanding of problems in 

the energy field, a concept of energy degradation has been worked out at a qualitative level. 

Describing some important examples within the concept, it was shown that energy problems 

governing our own lives may be explained and understood, at least in principle, without reference 

to thermodynamics. This is a basic requirement if we are to achieve energy awareness for then 

saving energy becomes a question of minimizing energy degradation, that is, seeking the optimal 

possibility of harnessing a given process to drive another useful process in reverse. For instance, 

realising that heating a room by dissipating electrical energy involves a large downgrading of 

energy may lead to a consideration of the possibility of harnessing this degradation to upgrade 

energy, that is, by pumping low temperature heat to a higher temperature as in the heat pump. 

According to the simpler version of our concept, saving energy means matching carefully the 

quality of the available energy forms with the quality of the energy required for a particular 

job. Finally, it has been shown that the concept of entropy may be conceived of as one possible 

way of describing energy degradation in a quantitative way. 

Only the major features of this concept of value, as applied to energy, could be sketched in 

this paper. We have confined ourselves to a few examples only. Application to further physical, 

chemical and biological problems may lead to an estimate of the range of the concept. It should 

be pointed out that the concept may be generalized to give a new understanding of economic 

problems where the principle of degradation is not yet generally accepted as fundamental (see 

e.g. Georgescu-Roegen [ 101 ). 

REFERENCES 

1. NUFFKELD FOUNDATION SCIENCE TEACHING PROJECT. Physics. 1 st ed. London, Longman, 1967. Revised 

edition: Revised Nuffild Physics. London, Longman, 1977. 

2. SCHLICHTING, H.J.; BACKHAUS, U. Energie als grundlegendes Konzept. Physik und Didaktik, Vo. 7, NO. 2, 

1979, p. 139. 

3. BRJLLOUIN, L. Thermodynamics, Statistics and Information. American Journal of Physics, Vol. 29, 1961, 

p. 322. 

4. SCHLICHTING, H.J.; BACKHAUS, U.; FARWIG, P. Das grune Blatt als Warmekraftmaschine. In: A Scharman 

(ed.), Vortrage der Fruhjahrstagung, p. 325. Giessen, 1978. 

5. BENT, H.A. Haste Makes Waste. Chemistry, Vol. 44,No. 9, 1971, p. 6'. 

6. BOLTZMANN, L. Der zweite Hauptsatz der mechanischen Warmetheorie. In: Popullire Schriften. Leipzig, 

1905. 

7. BACKHAUS, U.; SCHLICHTING, H.J. Die Einfuhrung der Entropie als Irreversibilitatsmass. Begriffsbildung 

und Zusammenhang mit der absoluten Temperatur. Der mathernatische und natunvissenschaftliche Unterricht, 

1981. 

8. BACKHAUS, U.; SCHLICHTING , H.J. Die Unumkehrbarkeit naturlicher Vorgange. Phanomenologie und 

Messung als Vorbereitung des Entropiebegriffs. Der mathematische und natunvissenschaftliche Unterricht, 

1981. 

9. ZEMANSKY, M.W. Heat and Thermodynamics. 5th ed. New York, McGraw-Hill, 1968. 

10. GEORGESCU-ROEGEN , N. The Entropy Law and the Economic Process. Cambridge, Mass., Harvard University 

Press, 1971. 

70

Part I1 

Energy Teaching in Secondary Schools

Energy teaching in schools 

Introduction 

The diverse range of approaches to teaching energy in schools throughout the world as evidenced 

by the collection of papers which follows suggests very strongly that there is a special difficulty 

inherent in the topic itself. 

As so often with words used by physicists, the word ‘energy’ had a refined, specialized meaning 

when used in a scientific context which it does not have in ordinary speech. My English dictionary 

defines energy as ‘force, vigour, activity’, all synonyms which do not commend themselves to 

a physicist. In such cases, it is very tempting indeed to point this out to the children and to start 

with a definition. But that step itself may lead to even greater problems than the one it sets 

out to cure. Consider the very common ‘energy is the ability to work’. What can the beginner 

with an open mind make of that? And how does his teacher respond to the obvious question 

about the meaning of ‘work’? James Clerk Maxwell had a much more graphic phrase when he 

talked of energy as ‘the go of things’. 

The truth is that the energy idea is not an obvious one. The concept itself came very late. It 

arose from the many experiments performed by distinguished physicists between, say, 1798 

when Rumford bored his cannon and the 1840s when James Prescott Joule was determining 

the so-called ‘mechanical equivalent of heat’ by so many different methods and when Hermann 

Helmholtz formulated the Law of Conservation (1 847). Entropy followed closely (1850). Ideas 

which arise so late in the history of a science always have inherent difficulties. And it is not hard 

to see why this is so. Energy cannot be seen; it cannot be heard; it cannot be felt. Indeed we can 

only detect it when it is undergoing some transformation or other. What is light? Energy in 

transit. What is heat? Energy in transit. What indeed is work? Energy in transit. 

If, as teachers, we believe that a child’s understanding of an idea comes through the use of that 

idea and that understanding grows through application, we must reject the adult, formalized 

approach which takes its starting point in a definition. And then we can introduce the idea very 

much earlier. Hence many present-day approaches introduce the topic of energy to children in 

the primary schools and so provide a firm basis in experience on which later formalized teaching 

may build. 

Even this does not rid us entirely of difficulties at the later stage. One recalls arguments about 

73


such a basic matter as the First Law. Henry Bent, in his delightful book ‘The Second Law’’ 

points out that ‘most people believe this law firmly; mathematicians because they believe it is a 

fact of observation; observers because they believe it is a theorem of mathematics; philosophers 

because they believq, it is intellectually satisfying, or because they believe no inference based 

upon it has ever been proven false, or because they believe new forms of energy can always be 

invented to make it true. A few neither believe nor disbelieve it; these people maintain that the 

First Law is a procedure for book-keeping energy changes, and about book-keeping procedures 

it should be asked, not are they true or false, but are they useful?’ 

In recent years, as energy has assumed greater and greater importance in the world at large 

with real shortages, high costs and a barrage of propaganda, any separation of energy teaching in 

physics courses in schools from the real world has become a real danger to understanding. It is 

clear from the contributions which follow, that this point is thoroughly accepted by forwardlooking 

teachers the world over. 

As citizens, we wish our students to appreciate the following things about energy, whatever 

else they leam about it in formal terms: 

1. Energy gets things done - it grows crops, drives machines, lifts loads, heats our homes, 

cooks our food, operates communication systems, keeps us alive and so on. 

2. Energy costs money (fuels, foods and the costs hidden in their production). 

3. Energy continually shifts from form to form - and in so doing may be applied to useful 

(and not so useful) human purposes. 

4. Energy ultimately derives either from the Sun or the nucleus. 

5. Energy is ‘conserved’ in the scientific sense; but, in the end, it is degraded to the form we 

call ‘heat’- and, unless at sufficiently high temperature, is virtually useless. 

Nothing there conflicts with the more formal approach we may wish to adopt with older 

students in the secondary schools. Indeed, that approach wil then be recognized for what it is - 

-a refinement of the intuitive view providing a necessary sense of proportion. 

These older students are exposed to a further trend - that towards a statistical view of heat 

processes. Teachers attempting to follow this trend wil find the comparative study of some of 

these approaches which has been prepared by JM. Ogbom especially valuable. It is therefore 

included at the end of this part. 

1. Henry A. Bent, The Second Law: An Introduction to Classical and Statistical Thermodynamics, New York, Oxford University 

Press, 1965. 

74

Japan 

The teaching of energy in Japan 

K. HIRATA. 

It is barely one hundred years since modern scientific thought was introduced into Japan. Nevertheless 

Japan today is not only at a high level in the scientific and technological fields, but is 

also having a great impact on Western society in many ways. We can assume that many people 

all over the world are interested in the sort of science education going on in Japan. The present 

situation in Japanese science education is described in several science education journals, but this 

is not enough. It wil therefore be appropriate to touch on some features of science education in 

relation to the theme. In the first section, some unusual characteristics of elementary science 

education are discussed briefly in connection with the teaching of energy. 

In the succeeding two sections, the outlines of energy teaching in lower and upper secondary 

schools are discussed. In Japan elementary and secondary education are controlled by the Ministry 

of Education which announces the course of study and revises it every ten years or so. In these 

sections, the content concerning energy described in the revised course of study is reviewed and 

some problems are discussed. 

Although the course of study is rather rigid, the teachers have considerable freedom in terms 

of methodology. Some teachers are trying to develop new teaching methods, some to devise new 

experimental apparatus; some study groups try to develop new curricula, while others investigate 

the process of understanding of important scientific concepts. 

In the final section, an example of curriculum development related to the teaching of energy 

is reviewed. 

SOME IMPORTANT FEATURES OF ELEMENTARY SCIENCE EDUCATION 

(1) Science is taught in all grades at primary school. 

Science is taught for two periods per week for the first and second grades (ages 6 and 7 years), 

and three periods for the grades from three to six. Each period lasts for 45 minutes. Language 

and arithmetic are basic subjects in Japan as in other countries, but a notable feature in Japanese 

education is that science is provided for all children at primary schools, even in the first grade. 

75


Opinions vary as to whether or not it is appropriate that science should be taught to such young 

children as an isolated subject. But after lengthy discussion, the Advisory Council for Courses of 

Study decided to continue science teaching as before [ 13. This decision is appropriate for a variety 

of reasons, e.g. where science is taught as a part of a language lesson, it can be predicted that the 

learning of science by observation would be given little attention in the present situation in 

primary schools. 

(2) Children learn science using authorized textbooks. 

All textbooks which are used at primary and secondary schools are edited by publishers following 

the guidelines in the course of study. These textbooks are inspected every three years by the 

Ministry of Education. Primary and lower secondary education are compulsory, and all textbooks 

which are used at these schools are given, not lent , to children. 

This system is effective in maintaining a high standard of compulsory education. But, on the 

other hand, it is also true that it restricts educational activities for both teachers and children. In 

addition, this system has a negative effect on the development of new curricula by various study 

groups. But, despite the fact that most primary school teachers are non-science majors, the 

system maintains high learning standards. 

(3) The content of subject matter is constructed systematically, 

According to the revised course of study the objectives of elementary science are to cultivate the 

abilities and attitudes of investigation, the understanding of natural phenomena and things, and 

to instil a love of nature [2]. Elementary science consists of three main domains, each with a 

solid structure. The emphasis on a systematic structure is a notable feature of elementary science 

in Japan. 

The three main domains for study are (A) living things and their environment, (B) matter and 

energy, and (C) Earth and universe. It wil suffice here to review the outline of structure and 

contents in domain (B). 

Domain (B): Matter and Energy 

(1) Characteristics of matter 

Substances which dissolve in water: dissolution and change, solubility and temperature, dissolution, 

concentration and conservation of quantity, acidity and alkalinity. 

The air: existence of air, elasticity of enclosed air, combustion and the change of matter, 

structure of a candle flame. 

(2) Interaction between matter and energy 

Weight and force: simple toys using weights and rubber-bands, action of weight and balancing, 

wind power and windmills, equal-arm balance, principle of the lever. 

Sound: sound and vibration, propagation of sound, power of sound. 

Light: sunshine and shadow, magnifying glass and sunlight, lenses and propagation of light. 

Heat: heat and temperature, expansion of volume by heat, conduction of heat. 

Electricity and magnets: playing with magnets, battery and bulb, magnetic needles and the 

action of magnet, simple electric circuits, electromagnet and its action. 

Although domain (B) relates directly to the concept of energy, teachers, needless to say, do 

76

Japan 

not teach energy concept directly. Instead, children are shown various natural phenomena, and 

tacitly made aware of the relationship between the change and energy. It is obvious that the 

teaching of energy concepts in elementary science also relates directly to domains (A) and (C), 

yet the explanation of these points is omitted here, 

From this brief description, it wil be understood that children are very busy learning lots of 

things. Some people insist that content in elementary science should be selected more carefully, 

and that the most important thing in science teaching is to give children the chance to investigate 

natural phenomena freely, with an inquiring mind. 

The process of inquiry which involves observing, classifying, measuring, inferring, and so on is 

very important in science teaching. Recently many teachers in primary schools have recognized 

this, but they usually have to struggle against a lack of teaching time. There are many problems 

to be solved for elementary science teaching. 

TEACHING ABOUT ENERGY IN LOWER SECONDARY SCHOOLS 

Science is taught for 105 periods per year for the seventh and eighth grades and for 140 periods 

for the ninth grade (one period is 50 minutes). Although the objectives of lower secondary 

science which are described in the revised course of study are almost the same as those for 

elementary school science, the following three points are particularly emphasized [3 1 . 

1. The formation of basic scientific concepts and learning by inquiry must be stressed as 

before. But special care must be taken to teach in accordance with the mental and physical 

development of a child. 

2. The content of the subject matter must be selected carefully to be basic and fundamental. 

3. Learning about the relationship between nature and human beings must be included in 

.science teaching. This means that basic knowledge about protecting the environment and natural 

resources and about energy problems in the world must be taught in the appropriate way. 

The spirit of revolution in science education which was engendered in the United States and 

in the United Kingdom in the 1960s was quickly introduced into Japan. The course of study of 

science for lower secondary schools which was proclaimed in 1969 emphasized that the process 

of inquiry and basic scientific concepts such as ‘matter and energy’ must be stressed in science 

teaching. As the result, such teaching was carried out earnestly by not a few progressive teachers. 

But it was also true that many others were perplexed by it. The problems were in much of the 

content studied, and in the formalization of the process approach. It is nonsense, for example, 

to make children memorize the patterns of inquiry! Since then, the revised course of study has 

come out. 

The science curriculum for lower secondary schools had originally the character of combined 

science, and consisted of two main domains (1) matter and energy, (2) living things, the Earth 

and the universe. 

The introduction to and the teaching of the energy concept are, needless to say, treated mainly 

in the first domain. In the previous science course of study, the concept of energy and its forms 

were introduced in the seventh grade, and the transformation of energy, and the concept of 

energy conservation in the ninth. But many teachers were critical for it is difficult, in general, to 

make children at the seventh grade understand such very abstract concepts as energy. This 

criticism had to be listened to. Energy is frequently defined as ‘the capacity to do work’. But 

the proper meaning of this neatly packaged definition is not simple to appreciate; moreover, this 

77


definition is incomplete. It is maybe true that ..... rather than beginning with a definition, a 

better eventual comprehension and appreciation of the significance of the idea of energy can be 

achieved through building an understanding of how the concept of energy can be applied to 

many phenomena’ [41. 

As a result of criticism by teachers, supervisors and others, the teaching plan for the energy 

concept was revised as follows. 

1. The teaching of the concept itself was omitted from the seventh grade, and replaced by 

studies of various closely related phenomena. 

2. The teaching of energy was transferred to the ninth grade. 

3. The teaching of energy conservation was transferred to the upper secondary school level. 

4. It was decided that material on energy resources, the effective utilization of energy, and 

the relationship between energy and the life of man should be taught throughout the course. 

The sequence relating to energy teaching is: 

(I) 

Force .......... seventh grade 

Objectives: To make children understand the basic characteristics and action of forces by 

thorough observation and experimenting. Although the term ‘energy’ is not taught, basic 

learning to build up the energy concept is planned. 

(1) The action of force: 

Force and the deformation of a spring. 

Force at a distance: electrostatic force, magnetic force. 

Gravitational pull, weight and mass. 

Unit of force. 

A force can be represented by an arrow. 

(2) The balance of forces: 

Balance of two forces. 

Balance of three forces which act on one point. 

Addition of forces, resolution of force. 

(3) Pressure and force: 

Characteristics of pressure. 

Pascal’s principle. 

Water pressure is proportional to depth. 

Buoyancy, Archimedes’ principle. 

(11) Electric currents .......... eighth grade 

Objectives: To develop the children’s understanding of various phenomena and the nature 

of electric currents by thorough observation and experiments. 

78 

(1) Electric currents and voltage: 

Conservation of electric currents. 

Introduction of voltage, Ohm’s law. 

Resistance. 

(2) Generation of heat by electric currents: 

Temperature change of water depends on the mass and amount of heat added.

Japan 

Amount of heat generated relates to the electric current, resistance and time. 

Electric power. 

Direct current and alternating current. 

(3) Electric currents and electrons: 

Vacuum discharge. 

Cathode rays consist of streams of negatively charged particles. 

Electric currents in metals; electrons. 

(111) Motion and energy . . . . . . . . . . ninth grade 

Objectives: Understanding simple motion of bodies and the work done by light, heat and 

electric currents, and developing the elementary concept of energy transformation. 

(1) Motion: 

Speed and direction. 

Frames of reference. 

Uniform motion in a straight line. 

Distance, speed and time. 

Free fall, acceleration of gravity. 

(2) Work: 

Definition of work. 

Work done against friction. 

Principle of work. 

Power. 

(3) Work done by light and heat: 

Light can do work. 

Heat can do work, work generates heat. 

(4) Electric currents and work: 

Electric currents produce magnetic fields. 

Magnetic field exerts force upon electric currents. 

Electric currents can do work. 

Work can generate electric currents. 

(5) Energy: 

Energy is measured by the work which can be done externally. 

Gravitational potential energy depends on height and mass. 

Kinetic energy depends on speed and mass; qualitative treatment. 

Transformations between potential energy and kinetic energy. 

Effective utilization of natural resources and energy. 

It is true to say that the strategy of the teaching of energy in lower secondary science has been 

much more improved by these changes. The reasons are that (1) children in the lower grades have 

experienced a range of phenomena which helps them to appreciate the idea of energy; (2) the term 

‘work’ has not been used as a name for a type of energy itself, nor has it been used as a rough 

name for mechanical energy; (3) the idea that ‘energy is measured by the work which can be 

done externally’ is an appropriate treatment for an introductory course, though not complete; 

(4) it is enough for the lower stages that various forms of energy are introduced, and that the 

convertibility of energy from one form to another is discussed; and (5) it is proper not to touch 

on energy conservation, because it needs quantitative treatment. 

79


The content which children have to learn in elementary science and in lower secondary science 

is extensive. Further examination is required to see whether learning by inquiry is possible. 

TEACHING ABOUT ENERGY IN UPPER SECONDARY SCHOOLS 

Although upper secondary education is not compulsory, about 93 per cent of the children who 

finish their lower secondary course now want to go on to upper secondary education in one form 

or another (generally, a three-year course). Upper secondary education has become quasicompulsory. 

Reflecting this situation and others, the course of study for upper secondary schools 

was revised in 1978 [ 51 . Six subjects have been set up in science. 

1. Science I: 4 credits, required at the tenth grade 

2. Science 11: 2 credits, selective 

3. Physics: 4 credits, selective 

4. Chemistry: 4 credits, selective 

5. Biology: 4 credits, selective 

6. Earth science: 4 credits, selective 

(1 credit: 1 period per week throughout a year) 

‘Science I’ and ‘Science 11’ are the subjects which are newly set up in the revised course of 

study for senior high schools. ‘Science I’ is a required subject for all students at the tenth grade. 

The objectives of the course are concerned with the basic principles and laws which relate to the 

motion of objects, change of substances, the evolution of living things, the balance of the natural 

world through observation and experiment, and the close relationship between nature and human 

lives. ‘Science I’ has the character of an integrated science with five main areas of study: force 

and energy (force and motion, the motion of a falling body, work and heat, transformation and 

conservation of energy); composition and change of substance (the various units which compose 

substances, elements, amount of substance, the mole, quantitative relations in chemical reactions); 

evolution (the cell and its division, reproduction and generation, heredity and variation, evolution 

of living things); the balance of the natural world (the motion of the Earth, form and state of the 

Earth, incoming and outgoing radiation, ecosystems and the circulation of matter); and human 

beings and nature (nature resources, solar energy, the utilization of nuclear power and the 

preservation of the natural environment). 

‘Science 11’ is intended for students who want to learn additional science after they have 

finished ‘Science 1’. This course has some unusual features. First, instead of following a definite 

syllabus, students may choose freely from three main themes. These are (a) observation of and 

experimentation with some specified phenomena, stressing the process of inquiry; (b) the investigation 

of a natural environment (field studies on living things or the local area) and (c) a case 

history of science studying the nature of intellectual activity in a scientific field with a historical 

approach to some important principles and laws. Second, a student may choose a theme freely 

from these three themes and can spend many hours on his study. Third, ‘Science 11’ offers a high 

degree of freedom to both teachers and students. 

Although this course is unique, it is questionable what fraction of the total enrolment at senior 

high school will wish to choose it. 

‘Physics’,‘Chemistry’,‘Biology’, 

and ‘Earth Science’ are subjects which provide an understand- 

80

Japan 

ing of basic concepts, fundamental principles and laws in each field and provide an opportunity 

to master scientific thought and methods on the basis of ‘Science 1’. These subjects are all selective. 

Some students do not take them at all, and some choose one or two according to their future 

courses. Today, the number of students who want to learn physics is decreasing gradually. This 

is a serious tendency from the viewpoint of physics education. 

Teaching of energy in ‘Science I’ 

Energy is one of the most important concepts considered in ‘Science I’, and it is closely related 

to all areas of the course. As already mentioned, the course is intended to develop students’ 

ability to consider natural phenomena in a unified way, so that the aim to make students understand 

nature in connection with energy is undoubtedly appropriate. The areas which relate 

mostly to the teaching of energy are ‘Force and energy’, ‘The balance of natural world’, and 

‘Human beings and nature’. 

Teaching in the area


of a falling body or projectile motion. Some student experiments which are intended to verify 

the conservation law have been planned. For instance, an investigation using a pendulum can be 

carried out. That is, the maximum velocity of a pendulum bob which is released from certain 

height is measured in various ways, and the maximum kinetic energy of the bob is compared 

with the potential energy lost by calculation. 

The main objectives of the learning about ‘heat and work’ are to make students understand 

that: (1) heat is generated by work: experimental evidence; (2) heat can do work: experimental 

evidence; (3) there is a certain relationship between the amount of heat Q and the amount of 

work W: W = JQ; the meaning of the mechanical equivalent of heat J; (4) heat is a form of energy; 

and (5) heat is a form of energy which relates to the internal state of substance. 

It is well-known that heat is one of the most difficult concepts for students to understand. 

Judged from the viewpoint of the first law of thermodynamics, heat is not internal energy itself, 

but the transfer of energy from one state to another. Heat is not a ‘quantity of state’ as kinetic 

energy is, but a ‘flowing form’ of energy. Therefore, there are some who insist that to use the 

term ‘thermal energy’ in physics teaching is inadequate, and a main cause of confusion [6]. 

It is really difficult for many students to identify the differences between ‘heat’ and ‘thermal 

energy’ and ‘internal energy’. A few physics texts do not use the term ‘thermal energy’. 

It is obviously inappropriate for the ‘Science I’ course to lead students into these discussions. 

But, it is important for students to understand the historical background, that is, that the relationship 

between heat and energy was developed against a background of industrial developments in 

the nineteenth century which had such an important impact on scientific theories [ 71. 

It is not planned to treat the idea of the first law of thermodynamics in ‘Science 1’. Therefore, 

the microscopic view of heat is not taught in depth. Laboratory work on the relationship 

between work and heat has been frequently planned in many texts in various ways. Forms of 

energy such as electricity, light, waves, sounds, etc. are introduced, and the transformation of 

energy from one form to another discussed. The general conservation law of energy is taught 

simply as a conclusion. 

Teaching in the area ‘Balance of the natural world’ 

The part of the syllabus which relates closely to the teaching of energy is concerned with 

‘incoming and outgoing radiation on the Earth’. Solar radiation is indispensable, directly or 

indirectly, for life on earth, and is also closely connected with phenomena in the atmosphere. 

An example of the sequence certain textbooks use is as follows: 

Energy coming from the Sun: amount of solar radiation and the solar constant, measuring 

the amount of solar radiation (student experiment), solar radiation and wave length, 

absorption of solar radiation by the atmosphere. 

Where does solar radiation go to? Energy the Earth receives and its effects, the balance 

between incoming and outgoing radiation. 

The transport of energy by the atmosphere: land and sea breezes, circulation of the atmosphere, 

moisture in the air, heat transport by moisture, heat-islands and the generation of 

typhoons. 

The transport of energy by ocean currents: ocean currents, vertical circulation of sea water. 

Circulation of water and other materials: circulation of water, substances which rivers 

bring into sea, substances ejected by volcanoes.

Japan 

The teaching in this area is carried out using a text, data, photographs, and reference books 

with a little laboratory field work. The problem is to devise interesting lessons in this field. 

Teaching in the area ‘Human beings and nature’ 

The objectives are to help students to understand the importance of natural resources, energy 

sources, and preservation of natural environment, and to make them recognise the relationship 

between human beings and nature. Three points are particularly stressed: (i) a world-wide viewpoint 

must be adopted; (ii) natural resources and energy sources in the Earth are not endless; 

and (iii) the activity of human beings must harmonize with the natural environment. 

A noteworthy feature of the teaching of energy in ‘Science I’ is that it has been developed 

synthetically and has not been confined within physics teaching. It is hoped that the purpose 

is achieved effectively. 

Teaching of energy in ‘Science I’ 

As already described, students can choose freely from three main themes and no more. Leaming 

about energy accordingly depends heavily on the wil of a student. If a student wishes, various 

kinds of investigation can be carried out. For example: (1) a case history of the development of 

the energy concept; (2) investigations on solar radiation; (3) experimental studies on the transformation 

and conservation of energy; (4) a study on ‘science in society’ which is centred on 

energy problems; and (5) society and the utilization of nuclear energy. 

The teaching of energy in ‘Science 11’ is an open field for teachers, and active studies in this 

field are expected. 

Teaching of energy in the Physics (optional) courses 

The physics course is taught four periods per week as standard for students in the eleventh or 

twelfth grade. One or two additional periods are available. Physics is chosen mostly by the 

students who wish to go on to further scientific or engineering studies, though the course itself 

does not aim specifically at science majors. 

The course covers four areas: force and motion, waves, electricity and magnetism, and atoms. 

The most important and basic concepts aimed at in this course are those of conservative quantities, 

wave nature, corpuscular nature, field, etc. Needless to say, energy belongs in the category of 

‘conservative quantities’, and is of great importance. 

The study of energy in ‘Science I’ is developed more fully, and is applied to various phenomena. 

The conservation law of mechanical energy is applied to many mechanical phenomena, such as 

circular motion, simple harmonic motion, waves, etc., and its great application is demonstrated. 

Gravitational potential energy in the general case is introduced, and the binding energy of satellites 

is studied in some schools. 

The kinetic model of a gas is another important example in which the laws of motion and the 

energy concept are applied powerfully. The equation of state for an ideal gas, the kinetic theory 

of gases, internal energy of an ideal gas, the first law of thermodynamics, etc. are treated in some 

depth. A microscopic viewpoint of heat is established by the study of relationship between heat, 

temperature, internal energy and the random motion of molecules. Laboratory work on Boyle’s 

law, Charles’ law, and the temperature change of gas in an adiabatic process is available. 

Needless to say, many ideas and phenomena in electricity and magnetism connect closely with 

83


energy. The relationship between an electric field and its potential, energy stored in a capacitor, 

Joule heating and electromagnetic induction are good examples. But the treatment followed in 

most textbooks is far from fresh. For example, the careful introduction and experimental 

development of the concept of electrostatic potential which the Nuffield Advanced Physics 

course has developed cannot be found in Japanese Physics texts [81. This concept and the 

relevant phenomena are among the most difficult for students to understand. Research into ways. 

of teaching this material is needed. 

The KBGK’ project started in Japan in 197 1. Much effort has been devoted by many teachers 

and professors since then, and KBGK physics books Vol. 1 and Vol. 2 were published in 1977 

and 1978 respectively [9]. KBGK physics is not a text for students, but a kind of reference book 

for teachers including many thoughtful suggestions for teaching physics. But, regrettably, it 

seems that many years may be needed to produce satisfactory results. 

A few studies on the teaching of dynamics which put stress on the energy concept can be 

found in Japan as well as in other countries [ 10, 1 13. According to many of these, the concept of 

force is more difficult to understand than the concept of energy for many children and students. 

The studies mentioned above started from the point of view that the leading actor in the 

traditional approach to dynamics was force, but that it would be preferable to cast momentum 

and energy in this leading role. This is a valuable opinion to listen to. But, regrettably, no concrete 

plan has yet come into existence. 

It is agreed that energy is an abstract and difficult concept to understand. But, even younger 

children today frequently use the term ‘energy’ though they do not understand its full meaning. 

Yet it is not difficult to introduce the elementary concept of energy appropriately into the 

beginning stage of introductory science, though this view is not held by many lower secondary 

school teachers. There are good-examples of it in many introductory science courses. We note, 

too, that it is the concept of energy rather than that of force which is most helpful in quantum 

physics. We may say that, in modern physics, energy is more fundamental than force. Such 

considerations encourage us to hope that energy-centred curricula wil be studied by a number 

of groups. 

Another unsolved problem in approaching the teaching of heat and energy concerns the use of 

the term ‘thermal energy’. In his comparative study on the teaching of energy, G.W. Dorling 

quotes the opinion of M.W. Zemansky: ‘The concept of thermal energy is by all odds the most 

obscure, the most mysterious, and the most ambiguous term employed by writers of elementary 

physics and by chemists’ [ 121 . This criticism applies to most Japanese introductory physics 

texts. There are several opinions about this, but little agreement. Reconsideration from the 

educational viewpoint is badly needed. 

A CASE STUDY: AN EXAMPLE OF CURRICULUM DEVELOPMENT 

It wil be appropriate to review an example of curriculum development which relates to energy 

in order to explain the new trends in energy teaching. The study was carried out by the group 

composed mainly of the members of Faculty of Education, Yamanashi University with the 

support of the science research funds of the Ministry of Education [ 131 . 

The objective of the study was to build the framework of a new integrated science curriculum, 

and to develop new teaching materials by investigating materials in ‘Science I’ and ‘Science 11’. 

1. ‘KBGK’ stands for the Japanese name for the study group organized in 1971 with the aim of improving the physics curriculum 

for upper secondary schools. It was specially supported by funds from the Ministry of Education. 

84

Methodology 

Japan 

There are several ways of organizing an integrated science curriculum. One is to establish a central 

theme for the course, and to build it by choosing appropriate materials from each domain of 

physics, chemistry, biology, and earth science. The study group decided to follow this line. The 

following themes were picked out and discussed: water, woods, the ocean, rivers, soybeans, 

slaked lime, motion, electricity, light, equilibrium, solar radiation, etc. 

After consideration, solar radiation was chosen as the main theme of the course because of its 

close relationship to ‘Science I’ and to today’s energy problems and because it includes a wide 

range of topics which are treated in conventional science courses. 

Construction and contents 

The theme of itself could tend towards applied science, but this would not be appropriate for an 

upper secondary science course. The contents chosen must be basic and important, common to 

those learned in ordinary science courses, but closely related to the theme. After consideration, 

it was decided to prepare the following four units: (I) the Sun, (11) solar radiation, (111) the 

effects of solar radiation on the Earth, and (IV) solar radiation and human beings. 

The framework of the curriculum, the sequence of teaching materials, and important laboratory 

work are outlined below. 

SOLAR RADIATION 

(I) 

The Sun 

Observing the Sun: form, size, mass, sunspots. 

Lab. : using a telescope, observing sunspots, change of appearance, radius of the Sun. 

Composition of the Sun: surface temperature, elements. 

Lab. : observing Fraunhofer dark lines. 

Movement of the Sun: southing (the moment when it crosses the meridian), shadow 

curve, distance between the Sun and Earth, spin and orbit of the Earth. 

Lab. : drawing shadow curve, measuring southing time, etc. 

(11) Solar radiation 

Variety of radiation: light, ultraviolet rays, infra-red rays, properties of light (propagation, 

reflection, refraction), heat. 

Lab. : mirrors, lenses, measuring refractive index, specific heat. 

Light as waves: diffraction, interference, dispersion, spectrum, wave length and colour, 

colour of substances. 

Lab.: diffraction and interference of ripples and light, prism and dispersion of light, 

absorption spectrum of colouring matter. 

Solar radiation and energy: wave length and distribution of energy, solar constant. 

Lab. : project of estimating surface temperature of the Sun. 

85


(111) The effects of solar radiation on the Earth 

Incoming and outgoing of energy at the Earth: incidence angle of sunlight, latitudeeffect 

of balance of heat, absorption and radiation of heat by the atmosphere, temperature 

change of the atmosphere, the ground, and water. 

Lab. : measuring amount of solar radiation, absorption of heat by the atmosphere, etc. 

The changes which occur on the surface of the earth: climate, circulation of the atmosphere, 

water erosion, sedimentation, weathering of rocks. 

Lab. : sedimentation, weathering of slaked lime. 

Historical aspects of solar radiation: periodic changes in various phenomena on the 

earth, glacial periods, fossil animals and plants. 

Lab.: periodic change of sunspots, observing annual rings of trees. 

The flow of matter and energy in ecosystems: solar radiation and behaviour of living 

things, growth of living things, mutation, evolution, photosynthesis, photochemical 

reaction, production and consumption of substances in an ecosystem. 

Lab.: germination, photosynthesis, photochemical reactions, micro-organisms and 

light, ultraviolet rays. 

(IV) Solar radiation and human beings 

(a) 

Direct utilization and harmfulness of solar radiation: heat effect of solar radiation, 

photochemical smog. 

Lab. : greenhouse, solar water-heating, solar furnace. 

(b) Indirect utilization of solar radiation: accumulation of solar energy, burning, fuels, 

fossil fuel, carbon compounds, food, clothing, synthetic fibres. 

Lab.: burning and dry distillation of wood, generating water and carbon dioxide by 

burning, conditions of burning, measuring combustion heat, experimenting with 

hydrocarbons. 

(c) 

Transformation and conservation of energy: various energy forms (heat, chemical, 

electric, and mechanical) and their transformation, conservation of energy and the 

first law of thermodynamics, energy degradation and the second law of thermodynamics. 

Lab. : storing of solar energy, solar cells, generating electric currents by wind power. 

(d) Various energy sources: tidal, terrestrial heat, nuclear power. 

Development of teaching materials 

On the basis of the content proposed, the following examples of teaching materials (including an 

outline of teaching and learning process) were developed. 

1. Observing Fraunhofer dark lines. 

2. Inferring the movement of the Sun from shadow curves. 

3. Measuring southing time and southing height of the Sun. 

4. Measuring refractive index in order to investigate characteristics of substances. 

5. Diffraction and interference of ripples and light. 

6. Estimating the surface temperature of the Sun. 

86

7. Measuring the amount of solar energy absorbed by the ground. 

8. Observing periodic changes of sunspots. 

Japan 

9. Observing behaviour of micro-organisms in order to investigate the effects of light and 

ultraviolet rays. 

10. Making a solar waterheater, or a solar furnace. 

11. Burning and dry distillation of wood. 

12. Measuring heat of combustion. 

In the above examples, readers may be interested in the estimation of the surface temperature 

of the Sun. The principle and method may be outlined as follows [14]. The experimental 

procedure is carried out using a home-made optical pyrometer, its parts being a standard electric 

lamp, an object lens, an eyepiece, pieces of filters which dim out light and protect eyes, and a 

lamp house. The relationship between the brightness and temperature of the filament of the lamp 

is determined beforehand. The surface temperature of the Sun can be estimated by comparing the 

brightness of the filament with the dimmed out brightness of the Sun. The result (5.8 X 103K) 

was fairly good. 

CONCLUSION 

Some important features of elementary science education in Japan were discussed in the first 

section. Although the content, extent and method are open to discussion, there is no doubt 

that elementary science plays a fairly substantial part. The spiral structure of the science curriculum 

has been revealed by the review and analysis of the teaching system for energy. The weakness 

of a spiral approach lies in the duplication of subject matter and it is clear that the teaching 

system for energy must be re-considered. 

The teaching of energy at the upper secondary level also requires re-consideration. To develop 

an energy-centred curriculum for dynamics and the use of the term ‘thermal energy’ in the teaching 

of ‘heat and energy’ are particularly important problems for study. It is worth emphasizing 

that learning about the relationship between energy and human beings has been emphasized 

throughout the science curriculum. 

In introducing this paper, the author wrote ‘. . . . many people all over the world are interested 

in the sort of science education going on in Japan.’ But, regrettably, it appears that science 

education in Japan is still very busy discovering how best to make learners understand or absorb 

important scientific knowledge. The effectiveness of science education in Japan depends very 

much on diligence of learners as well as on a high level of technology which itself depends on the 

industry of Japanese people. One important objective of science education in Japan today is to 

establish an education system which stresses humanity and creativity. Severe and wide reconsideration 

of current practice is required to this end. 

87


REFERENCES 

1. JAPAN. ADVISORY COUNCIL FOR COURSES 0 F STUDY, MINISTRY OF EDUCATION. On Innovation Of the 

Curriculum. Tokyo, 1976. (In Japanese.) 

2. JAPAN. MINISTRY OF EDUCATION. The Course of Study for Primary Schools. Tokyo, 1977. (In Japanese.) 

3. JAPAN. MINISTRY OF EDUCATION. The Course of Study for Lower Secondary Schools. Tokyo, 1977. (In 

Japanese .) 

4. PHYSICAL SCIENCE STUDY COMMITTEE (PSSC). Physics; Teachers’ Resource Book and Guide. 2nd ed. 

Part 3, p. iii. Boston, Mass., Heath, 1965-66.4 Vol. 

5. JAPAN. MINISTRY OF EDUCATION. The Course of Study for Upper Secondary Schools. Tokyo, 1978. 

(In Japanese.) 

6. YAOTOME, M. et al. Confusion in the Concepts of Heat and Other Related Subjects in Senior High School 

Physics. J. Phys. Ed. Soc. of Japan. Vol. 29,38,1981. (In Japanese.) 

7. TheProject Physics Course, 6 Units, Unit 3,46. New York, Holt, Rinehart and Winston, 1970. 

8. Nuffild Advanced Physics Teachers’Guide, Unit 3,7. Harmondsworth, Penguin, 1971. 

9. ISHIGURO, K. et al. KBGKPhysics. Asakura Shoten, 1978. (In Japanese.) 

10. ISHIKAWA, T. Development of an energy-centred curriculum for mechanics. J. Phys. Ed. Soc. of Japan. 

Vol. 15,1,1967.(In Japanese.) 

11. TONOKI, H. The teaching of mechanical energy and its understanding. J. Pkys. Ed. Soc. of Japan. Vol. 19, 

35,1971. (In Japanese.) 

12. DORLINC, G.W. In: J.L. Lewis (ed.), Teaching School Physics. Harmondsworth, Penguin, 1972. (Unesco 

Service Books on Curricula and Methods.) 

13. IDE, K. et al. Development of Integrated Science Materials for Upper Secondary Science. J. Sci. Ed. in Japan. 

Vol. 5, 1, 1981, pp. 9-14. (In Japanese.) 

14. HIRATA, K. et al. Estimation of Solar Surface Temperature. J. Phys. Ed. Soc. of Japan, Vol. 29, 18, 1981. 

(In Japanese.) 

88

India 

The teaching of energy in India 

B. SHARAN 

In India, Education is organized in a way which gives every state and union territory the liberty 

to frame its own school curriculum. That science should be a part of the school curriculum is 

universally recognized. In 1975, the central government recommended the adoption of a new 

pattern of education called the 10+2 pattern. This was done with a view to bringing about some 

sort of uniformity in standards in education throughout the country and to ease mobility 

between one part of the country and another. The main feature of the 10+2 pattern of school’ 

education is 10 years of undifferentiated school education and 2 years of vocational or or preparatory 

education for professional and academic courses. The teaching of science is compulsory 

from class I to X in the 10+2 pattern of education and optional at the +2 stage. All the states and 

union territories have agreed in principle to adopt the 10+2 pattern of education, but the date 

of commencement and implementation differs from state to state and in some cases still remains 

to be decided. In the National Council of Educational Research and Training (NCERT) pattern, 

it is recommended that science be taught as ‘environmental studies’ from classes I to V, as ‘integrated 

science’ from classes VI to VIII, as ‘combined science’ from classes IX to X and as separate 

disciplines at the +2 stage. Knowledge - and therefore the teaching - of energy at all the school 

stages, primary classes I to V, middle classes VI to VIII, secondary classes IX and X and +2 stage, 

classes XI and XII, is considered to be essential and accordingly it forms an integral part of the 

science/physics curriculum. 

The school science curriculum for various stages is mostly concept centred; accordingly, energy 

is generally introduced either from a conceptual or academic point of view. In the conceptual 

framework, one deals with the meaning, definition, its relationship with work and measurement 

of energy whereas on the academic side, the emphasis is on teaching conversion or transformation 

of energy from one form into another and conservation of energy during all processes of transformation. 

For example, at the primary stage in Environmental Studies Part I1 for class IV, the 

concepts dealt with are described as ‘different objects get their energy from different sources, in 

rubbing, energy of our hands gets changed into heat energy, transformation of energy from one 

form into another is shown by using a yo-yo disc’. At no place has energy been used as an 

integrating factor for the development of science courses. 

The fact that sources of energy were limited was of interest to academics, and the students 

89


were exposed to it mostly at the undergraduate and postgraduate levels, particularly while 

discussing the life span of the Sun. Since this meant dealing with billions of years, the problem 

never appeared to be of immediate interest. At the government level there had been a concern 

about the utilization of energy from coal, which became more pronounced with the findings 

of one of the official committees that a phenomenally large percentage of this energy was being 

spent in hauling coal! This led to the change in emphasis of having more diesel or electric 

driven engines to haul coal. This however did not have any effect on the lifestyle of people. 

That we were at the brink of an energy crisis, appeared to be quite clear when in 1973 prices of 

petrol and petroleum products went up almost by 300 per cent, when the common man started 

to feel that he was hit below the belt. For the first time there appeared to be a realisation that 

energy was a part of life; that, in its absence, all activities would cease and that the availability 

of present forms of energy may not be infinite. Since then there has been a growing consciousness 

about the use and discovery of alternative sources of energy. People are being made aware 

both through formal and non-formal channels. It is clear that finding alternative sources of 

energy is a matter of life and death, in absence of which our entire national economy will be in 

jeopardy. The country will not be able to afford mounting fuel bill costs in foreign exchange 

and the consequent high rate of inflation. 

It took about six years for the pressures to mount up; then, in 1979, the Indian Science 

Congress felt the need for a nationwide concentrated effort to tackle the energy problem. 

Accordingly, it was decided to have ‘Energy Strategies for India’ as the focal theme for the sixtyseventh 

session of the Indian Science Congress held at Calcutta, 1 to 5 February 1980. Some of 

the recommendations relating to science education are: 

‘Science and technology should be taken to every home. That should be our national aim. The 

Vignan Parishads (e.g. the Bangiya Bijnan Parishad, Marathi Vijnan Parishad, Gujrati Vijnan 

Parishad) or similar organizations like Indian Science News Association should be given adequate 

grants by the Government.’ 

‘The broad thrust of energy management at the household level should focus on food, feed, 

fodder and fuel as follows: 

1. Home Science and Nutrition education should become part of the curriculum and should 

include some basic features on future strategies for energy. 

2. With a view to reducing energy expenditure on fuel for cooking foods, the concept of 

community kitchens should be explored. 1 

3. Surveys should be made to assess the extent of food/energy wasted at household level, 

eating places, festivals/marriages, etc. to focus attention on measures for reducing such wastage, 

its conservation and better utilisation. 

4. The syllabus in the school stages (high school/higher secondary) should include some basic 

information on energy sources, conservation and utilisation - and some work experience in this 

regard. 

5. Home Science Colleges in traditional Universities should undertake research projects 

related to total energy dynamics at the individual farmer’s household level in the current context 

of improved technology cropping and live stock farming systems applicable at this level. The total 

energy dynamics study should include energy, input/output for food, feed, fodder and fuel 

needed for the maintenance of the family/household.’ 

The recommendations of the sixty-seventh session of the Indian Science Congress have recently 

been circulated; their implementation in part or full, at the formal level wil take its own time. 

90

India 

It is difficult to visualize the precise date of implementation without working out all the details 

considering fully the constraints and the facilities available. No deadline has been set by the 

Indian Science Congress. This is to be noted in the context that ours is a state controlled system 

of education and therefore introduction of formal curricular changes become possible only after 

discussions at various levels of policy, their acceptance by states and the issue of corresponding 

directives. 

However, there had been several efforts at the non-formal level to relate energy studies to the 

real world of the energy gap, to the utilization and waste of energy etc. These non-formal efforts 

can be broadly divided into two categories, (i) relating to a systematic development of topics 

that can be taught to school children and (ii) through exhibitions and mass media. The earliest 

available literature that I can lay my hands upon is from the Vikram A Sarabhai Community 

Science Centre, Ahmedabad, which produced Integrated Sciences Trial Topics on Energy’ in 

1975, where topics covering different aspects of energy that can be taught to school children 

have been developed in a very systematic manner, The complete spectrum of energy has been 

covered under fourteen headings, namely: 

1. Energy and You 8. Chemical Energy 

2. Energy Transformations 9. Nuclear Energy 

3. Mechanical Energy 10. Energy in Living Organisms Part I 

4. Machines 1 1. Energy in Living Organisms Part I1 

5. Light Energy 12. Energy in Living Organisms Part I11 

6. Heat Energy 13. Power Production 

7. Electrical Energy 14. Sources of Energy 

The topics that are of direct relevance for the present purposes are ‘Energy and You’ and 

‘Sources of Energy’. Under the heading ‘Energy and YOU’ the subtopics of interest dealt with 

are ‘The Conservation of Energy’ and ‘Einstein’s Ideas’. Under ‘Sources of Energy’, the points 

that have been emphasized are (i) the sun is a major source of energy; (ii) large parts of OK 

energy needs are met from coal, petroleum or natural gas, (iii) our energy needs are increasing, 

requiring us to tap known and unknown sources of energy without polluting the earth. The 

description is followed by a table giving consumption of per capita energy on food, home consumption, 

industry and agriculture, and transportation through the ages. 

The chapter ‘Energy sources on the Earth’ discusses two major topics, Conventional Sources of 

Energy (classification by the present author) and Future Sources of Energy. The conventional 

sources of energy include coal, petroleum, using potential energy of water and nuclear energy. 

Under ‘Future Sources of Energy the discussion considers seven subheadings, namely (i) Solar 

Energy; (ii) Wind Energy; (iii) Tidal Energy; (iv) Geothermal Energy; (v) Fast Breeder reactors; 

(vi) Fusion Power or Energy from Fusion and (vii) Gobar Gas (energy from plant and animal 

waste). The chapter concludes by defining the unit of energy that must be used when discussing 

sources. The unit introduced is ‘Q’, equivalent to 2.98 X 1014 kWh or 1.06 X 1021 joules, projecting 

the energy requirement for the next hundred years in the range of 100 Q. 

At the national and state levels, the mass awareness programmes about the problems relating 

to energy were organized through science exhibitions by having specific related sub-themes. 

NCERT has been organizing National Science Exhibitions (NSE), for children in collaboration 

1. Monograph, 90 pp. 

91


with other organizations since 197 1. The 197 1 NSE was organized by NCERT in collaboration 

with the University Grants Commission (UGC). Since 1972, the Jawahar La1 Nehru Memorial 

Fund (JNMF) has been collaborating with NCERT in its efforts to popularize science through 

exhibitions. They have been jointly sponsoring state-level Science Exhibitions since 1978. Since 

1974, the organization of the science exhibitions has been based on thematic considerations, 

eight to twelve in number. The theme and subthemes are sent for guiding the states for the 

organization of their exhibitions. One of the subthemes had been ‘Energy and Power’ in 1974, 

‘Energy and Fuels’, 1975 to 1979 and ‘Energy Generation and Needs’ in 1980. The areas covered 

by the exhibits mostly pertain to the use of solar energy, wind power, nuclear power generation, 

fuel from wastes (gobar gas, nutty gas), economy in use of energy, etc. The following table gives 

an idea about the types of models displayed in various exhibitions. 

TABLE 1. Some of the models displayed on energy and fuels in various National Science Exhibitions for children 

in India. 

Exhibit Description BY 

1974 

Solar cooker The model displays a solar cooker working De Souza’ School, 

on the principle that solar energy can be used Sector-2, 

for heating purposes. 

Rourkela. 

Home-made Displays the model of a lantem-cum-stove Shukrawar Peth, 

lantern-cum-stove working on the principle of combustion Jagatap Wada, 

and ventilation. 

Poone-2. 

Model of Displays a model which generates electricity Modem School, 

hydro-electric by the use of water. Barakhamba Road, 

power station 

New Delhi. 

Power economy in 

street lighting 

The experiment tries to economize the 

wastage of power in street lighting by 

switching them off and on at specified 

needed times by the introduction of 

photocells in the circuit. 

Andrew’s High School, 

33, Gariahat Road, 

Calcutta. 

1976 

Bombay High A model displaying first Indian attempt Narendra Vidya, 

Drilling Project in off-shore oil (petroleum) exploration Mandir, 

to meet country’s demand. 

Calcutta. 

19 77” 

Solar water heater - Maharani Churnabai 

Higher Secondary School, 

Dewas (MP). 

Economy of heat - Narendranath 

energy and proper 

Vidyamandir 

utilisation of 

reserved coal of India 

*Descriptions for 1977 are unfortunately not available. 

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1979 

Solar energy air 

A model of a device for regulating room KJP Girls’High School, 

conditioning temperature. Mission Compound, 

Shillong, Meghalaya. 

Wealth from 

waste 

Displays model of a biogas plant using cowdung, 

water hyacinth plants and chicken excreta with 

water. 

Faith Academy School, 

13/15 East Pate1 Nagar, 

New Delhi. 

Oil flows, 

A semi-working model of Ankleshwar oil M.T. Girls’High School, 

the nation grows project. Surat. 

1980 

Multi-purpose 

Working model for the conservation of solar St. Anthony School, 

heat pipes from energy. Doranda, 

solar energy 

Ranchi. 

Solar distillation 

Working model for the conservation of solar Government High School, 

plant energy. Majra. 

Nutty gas 

Power from 

sea waves 

Shows the preparation of nutty gas from 

coconut. 

Model of energy generation from tidal 

waves. 

India 

The Bhawanipora Education 

Society College, 5-Lala 

Lajpat Rai Sarani, Calcutta. 

Government High School, 

Muthalanda, 

Palghat, Kerala. 

Solar water heater Use of sun’s heat for heating water and 

Government Senior Model 

and house heating warming houses. School, 

system 

Civil Lines, Patiala. 

Electricity from Generation of electricity from the soil. Government Higher 

soil 

Secondary School, 

Rajgarh, Beyavara. 

Cooking gas 

A burner operated on diesel, petrol or 

Government Higher 

plant kerosene gas. Secondary School, 

Ringas (Sikar). 

Grain drier 

A working model of solar energy based on 

grain drier. 

C.D. Inter College, 

Haldaur (Bijnor). 

For the benefit of the school students and teachers, NCERT also produces a booklet, Structure 

and Working of Science Models, giving brief descriptions of some selected exhibits more or less in 

the form in which the write-ups were presented by the participants. 

From time to time, mass media have also made efforts to make the public aware about the 

problems relating to energy. For example, All India Radio broadcast two lectures on Bharat me 

Urja Srot Aur Uski Sambhavnayen [Sources of Energy in India and its potentialities] by Dr. A.R. 

Verma, Director, National Physical Laboratory, in 1978 under the Dr. Rajendra Prasad Lecture 

Series. The lecture was delivered in Hindi, the official language of the country. Some of the 

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topics discussed were oil, hydroelectric power, nuclear energy, solar energy, research in solar 

energy, bioconversion, geothermal energy, wind power, energy from the sea, etc. 

At the formal level the present author has prepared a module on Momentum and Energy 

addressed to the secondary and senior secondary teachers. Out of 136 pages, 88 are devoted to 

energy. The topics dealt with at length are energy conservation, energy requirements, nonrenewable 

and renewable sources of energy, solar energy and fusion energy. 

For example, under energy requirements, attention is drawn to the fact that our (world) 

energy requirements are growing at a fantastic rate. The estimated energy consumption between 

1870 to 1970 A.D. was about half of the total from 1 A.D. to 1870 A.D. The requirement during 

the next century is expected to rise by a factor of 25 of that during the last century. So there is 

a need to search for new sources of energy that can sustain the growing demands on energy. 

Under non-renewable sources of energy the attention is focused on the energy crisis that the 

world is likely to face in view of the threat that petroleum and coal reserves are not likely to 

last long, the conservative estimates being next 50 years (i.e. 2030 A.D.) for petroleum and next 

100 years (i.e. 2080 A.D.) for coal. The possibility of averting the crisis lies only in economizing on 

fuel consumption, utilizing and exploring the renewable or alternate sources of energy such as 

solar energy and energy from bio-wastes. The efforts of Petroleum Conservation Research Association 

(PCRA) have highlighted that by careful use, even a 5 per cent saving on petrol may result 

in an annual national saving of about 200 crores of rupees (about 250 million U.S. dollars) at 

present prices. 

As mentioned earlier, in the school textbooks produced at the national level (i.e. by NCERT) 

as well as at the State level, energy has not been used as an integrating factor. However, in the 

latest editions, the relevance of energy to different aspects of life has been emphasized in different 

classes at suitable places. If a 16- or 18-year-old student who has passed class X or XI1 tries 

to recall everything he has been taught about energy, he is likely to arrive at some integrated 

picture about the problems relating to energy; otherwise the picture is a very disjointed one. For 

example, the concern about the growing energy demands and limited energy resources has found 

its place in Environmental Studies Part II, a textbook for class IV which teaches pupils that we 

need energy to do work and to move fans and machines and that different objects get their 

energy from different sources, e.g. muscular, mechanical, electrical etc. In Learning Science Part I 

for class VI, the students learn that the sun is the main source of energy on the earth, that almost 

all sources of energy on earth are due to the sun, that man’s energy requirements are increasing 

and that present sources of energy are likely to run out. The amount of natural fuel available 

on earth is limited and therefore economy must be practised in the use of energy in daily life. 

Students are also taught that there are different forms of energy and that one form can be converted 

into another. 

In Learning Science Part 11 for class VIII, the quantitative aspects of energy, and particularly 

of electrical energy, are dealt with in detail. The concept of nuclear energy as an alternative 

source is also introduced. 

In Science Part I for class IX, the concept that there are different sources of energy (the sun, 

fossil fuels, biogas or gobargas) is again emphasized. In Science Part 11 for class X, the quantitative 

aspects of electrical and chemical energy are dealt with in greater detail. 

In Physics for classes XI and XII, the quantitative aspects of mechanical, electrical and nuclear 

energy are dealt with in greater depth. The law of conservation of energy is introduced through 

the First Law of Thermodynamics. 

Lastly, special efforts are being made to introduce the concepts of energy at the primary stage, 

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India 

age group 6 to 11, classes I to V, through the United Nations Children’s Fund (Unicef) assisted 

Nutrition Health and Environmental Sanitation Programme. Under the supervision of NCERT, 

five regional centres for the development of this programme for the primary stage were established 

at Baroda (Vadodra), Calcutta, Coimbatore, Jabalpore and Ludhiana. The materials developed 

at Ludhiana Centre deal with topics such as energy requirements during pregnancy and lactation 

of mother and infants, energy value of food etc. In the materials, produced by the Coimbatore 

Centre, foods are classified into three categories, one being energy (giving) foods. Some of the 

descriptions are as follows: 

‘The body needs energy for its activities as a railway engine needs coal to make it go, or a car 

needs petrol to move. The human body is never at rest, it is always engaged in work. Even when 

we sleep, the heart beats, the chest walls move. . . food is the fuel supplying energy.’ 

‘All foods give you some energy, but the most important energy foods are those having a large 

amount of starches, sugar and fats in them.’ 

‘Energy foods which contain starch are bread, cereals and starchy vegetables, such as potatoes, 

tapioca and sweet potatoes. Other energy foods taste sweet such as sugar, syrup,jaggery and 

honey.’ 

In short, in India a considerable amount of energy consciousness has been generated through 

non-formal media, but the formalization of these efforts will take some time to develop. 

95


The teaching of energy in Qatar 

N.H.A. GALIL 

The University of Qatar was opened in 1972 starting with two faculties of Education, one for 

men and one for women. After that, faculties of Science, Arts and Languages, Social Sciences, 

Islamic Religion and Law, and lastly a faculty of Engineering for men was opened in September 

198 1. Further expansion is planned when the University moves to permanent buildings in 1982. 

The educational ladder in Qatari schools has 6 primary grades, 3 preparatory and 3 secondary. 

From grades 1 to 10 all children, boys and girls, study the same subjects with home economics 

as an extra subject for girls. At grade 1 1 students have to choose to major either in sciences or 

literature. Those who major in sciences drop the study of social sciences and concentrate on 

mathematics, physics, chemistry, biology and earth sciences, while those who choose to major 

in literature concentrate on social sciences (geography, history, philosophy and sociology) but 

still study applied sciences and applied maths at the rate of 2 periods per week for each. Both 

divisions follow basic courses in Islamic Religion, Arabic and English Languages. 

TEACHING ENERGY IN QATAR1 SCHOOLS 

Energy is not taught in the schools in Qatar as a separate course, but as a principal theme that 

integrates many diverse concepts in science. It extends throughout the science curriculum from 

grade 1 to grade 12. 

Energy as a topic is not only related to sciences, it also relates strongly to economics, civics, 

political sciences and other fields of social studies. It can also relate to mathematics to make 

abstract knowledge clearer to children. Unfortunately, the curriculum development process in 

Qatar did not take the holistic form which is normal procedure in most third world countries, 

where the emphasis and priority are given to a particular domain of knowledge on the assumption 

that it is most nearly related to the developmental needs of the country. This is the situation 

with science education and is one of the reasons why we read about so many innovatory projects 

in this field. 

It is unfair to discuss energy education in isolation from the aims of science education and the 

approach adopted in its design which determine the weight and role of energy in that design. The 

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Qatar 

decision to include a study of energy in the science curriculum came naturally as an integrating 

theme in the programme design and as a field of knowledge that relates science and technology 

and their interaction with human life. 

The role of science in a developing country is different from its role in a developed country. 

First, science has to be a tool for solving national problems and for directing the nation’s development 

plans along the right path. Thus one of the principal tasks in the curriculum development 

process is to identify these problems and to relate them to the overall development plans of 

society. These considerations determine what to teach and the aim to be achieved in the teaching 

process and help to determine the way these topics are taught. 

Qatar is a rich oil producing country which gained independence in 1971; a new era of 

modernization began. Many serious problems arose from the big gap between the needs of 

development and the lack of scientific and technological personnel able to carry out the plans. 

Whilst dependence on expatriate experience might solve the problem temporarily, a long-term 

development plan must require that able native personnel be prepared for the work. Unfortunately 

science courses in the schools, whether primary, preparatory or secondary, were not attractive to 

the majority of pupils (as shown by a study done in 1973). In a study undertaken to investigate 

this phenomenon, the factors primarily responsible were found to be: (a) the science curriculum 

was irrelevant to the needs of children and of society; (b) the topics taught had no functional 

role either in the everyday activities of the children or in relation to the environment; (c) the 

instruction method was mainly traditional ‘talk and chalk’ in which the teacher adopted the 

frontal position of information dispenser, forcing the children to take a passive role; (d) the sole 

aim of education in general and science education in particular was to promote the recall of 

information in the form of facts, laws and the detailed description of things and phenomena; 

and (e) the educational materials prepared to translate the curriculum into instructional situations 

consisted solely of badly written and printed books, with unhelpful illustrations. 

This was the starting point for the innovation process. We had to find how to build or design 

a science education programme that: (1) avoided the deficiencies of the previous programme; 

(2) met the needs for the development of the society; (3) developed interests in science and in 

the selection of science as a career; (4) made science a sensible and practical experience so that 

people could use it as a tool to facilitate their interaction with the technological and scientific 

trends which were invading all aspects of their life; and (5) helped to solve the problems deriving 

from exposure to science and technology without being prepared to think and behave in scientific 

and technological terms, (such problems are primarily concerned with attitudes and values). 

We were able to recognise certain factors that helped us to decide which approach to adopt 

in tackling this task. 

Science today has to be looked at as a system of interacting components - knowledge (in 

the hierarchical form of facts, concepts, principles, etc.); methods of arriving at this knowledge 

and interaction with human life. This three-sided system defines what we mean by science in the 

Qatari schools. 

Science is a unity: although at one time it was divided into separate disciplines, this was only 

a convenience for research purposes. When science research developed so greatly in the last half 

century, science moved naturally towards unity with the creation of such interdisciplinary fields 

of knowledge as bio-physics, bio-chemistry , and oceanography. 

Science and technology are two faces of the same coin; any attempt to separate them is 

prohibited by the nature of their interdependence. Science provides the theory for technology 

while technology creates more problems for science to tackle and so on. 

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Men can use science to enrich their lives. To the ordinary man, science is the tool that synthesizes 

medicines to save his life, that invented the telephone, television, etc. This means that science is 

seen to be functional in nature. 

Learning is a function of age, on one hand, and of motivation and interest on the other. It 

can continue as long as it results in rewarding the learner. With this in mind, we envisaged a 

science curriculum which would take the environment as an integrating theme, provide highly 

motivating activities aimed at a better understanding of contemporary problems, and develop 

the ability to work co-operatively towards appropriate solutions to these problems. 

Energy is basic to the environment; in addition, after the oil embargo of 1973 in what came to 

be known as the ‘Energy Crisis’, it was given wide publicity. It presents a major problem both at 

international and national levels. It is related to political and economic strategies in both the 

developed and the developing worlds, and it has a powerful impact on both consumer and 

producer countries. It is the most important issue for this generation and for many generations 

to come. Decisions which this generation takes wil surely shape the life of the coming generations. 

Thus those decisions must be based on understanding of all sides of the problem. But good 

decision making is not an inborn talent; rather, it is a skill that has to be developed. The gaining 

of understanding and the developing of decision-making skills are among the long-term tasks of 

education. 

TEACHING ENERGY IN THE PRIMARY SCHOOLS 

A conceptual scheme was designed for primary school science education. The context of investigation 

is the environment with its six interacting components: man, animals, plants, matter, 

energy and natural phenomena. 

Man is viewed separately from animals on a religious basis that considers man to be a distinct 

creation and not one developed from animal ancestors. Matter and energy are treated as two 

separate entities for the sake of simplicity, yet the relationship between them is made clear as 

the student moves towards generalization. 

In each of these environmental components, we attempt to build up six basic concepts: diversity 

versus unity, change versus balance and equilibrium, adaptation for survival, resources, investment, 

interaction. This list does not imply any hierarchical sequencing. 

Because children of primary school age are known to have short attention spans, we preferred 

to design short modules depending mostly on investigations and inter-group discussion of what 

they have found out during their activities. As this approach was new to the teachers in Qatar, we 

distributed these modules for the six primary school grades on the basis of their level of difficulty, 

taking into consideration that the subconcept which children form,at one grade could be used as 

a basis for the higher order subconcept in the following grade. In addition to the vertical hierarchy 

of sub-concepts, the conceptual scheme features horizontal inter-relations between the modules 

studied in one grade. 

The modules on Energy and the grades in which they are taught may be listed thus: 

1. Electrical equipment at home - ‘what gets them working?’ 

2. Means of transport - ‘what gets them moving?’ 

3. What is ‘Energy’ and what ‘Forms of Energy’ do we know? 

4. How our body gets the energy it needs. 

(grade 1) 

(grade 2) 

(grade 3) 

(grade 4) 

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5. 

6. 

7. Coal and oil are the most important sources of energy. 

8. 

Energy can be transformed from one form to another. 

We can use energy transformation for our benefit: 

at home, in industry and in transport. 

Electrical energy, a clean and transportable form of energy: 

how to produce or generate it. 

9. Energy causes changes in matter (e.g. expansion). 

10. Solar energy is the origin of all natural forms of energy known. 

(grade 4) 

(grade 5) 

(grade 5) 

(grade 6) 

(grade 6) 

(grade 6) 

An example : Module 5 : ‘Energy Transformations’ 

Objectives: 

(a) 

Cognitive. 

By the end of this module students can:- form the concept that energy can be transformed 

from one form to all other known forms, through such subconcepts as: Electrical 

energy can be transformed to mechanical energy (motion), heat, light, sound, magnetic 

and chemical energy. 

(b) Psychomotor (mental and manipulative skills). 

1. connect an electric circuit following a circuit diagram. 

2. make up simple apparatus from its components. 

3. handle materials carefully. 

4. make a thorough observation and report it both orally and in writing. 

(c) Affective. 

Appreciation of the role of science in enriching our life and making things easier as in the 

case of the invention of accumulators, dynamos, heaters, etc. 

Activity No. 1 

Objective: To examine one device for the transfer of electrical energy into heat and light. 

Materials needed: An office fluorescent lamp, a heating coil, both working off batteries (for 

demonstration). 

Suggested approach: 

1. Show the equipment to your students and let them examine it for some time to recognize 

what it is and what each item is used for. 

2. Open the container of the batteries at the bottom of the office lamp and let one of the 

students take them out, distribute them for examination and recognition. What are these things 

called, and what are they used for? 

3. Ask the children the following question: 

Do we have to put the batteries in their container in any particular way? And why? 

Let them examine both the batteries and the container to discover the answer, then let them 

try to put them in correctly and put the light on. 

4. What is the function of the fluorescent lamp? 

Discuss the question with the children to help them express the idea in scientific language. 

99


‘The lamp transfers electric energy into light energy’. 

5. Move to the other equipment and ask them what is the use of the coil? 

What form of energy is produced from the coil? 

6. Ask your children to report the conclusion they have arrived at from these two investigations. 

7. Ask them to list other things that produce the same transformations of energy 

Activity No. 2 

1. Discuss with them what is meant by chemical energy and let them give examples that show: 

(a) release of chemical energy, 

(b) absorption of chemical energy. 

2. Ask them about the car battery and how it works. What could one do if the battery of 

one’s car died away? 

3. Try to get an old battery (demonstration accumulator) whose plastic case is semi-transparent 

so they can see the oxygen bubbles coming out during the chemical reaction of charging. 

What causes the chemical reaction? 

What transformation of energy is involved in charging a battery? (electrical - chemical) 

The module goes on to cover the transformation of each form of energy to other known 

forms, through investigations and experiments done by the children themselves, demonstrations 

done by the teacher, and through recommended reading and class discussion. 

At the end of the module children are asked to write a paragraph about some useful energy 

transformations which could be utilized for human benefit. 

TEACHING ENERGY IN THE PREPARATORY SCHOOLS: GRADES 7-9 

The curriculum design for preparatory schools, grades 7 to 9, includes an integrated environmental 

science course bringing together various conventional sciences and social sciences (physics, 

chemistry, biology, climatology, astronomy, oceanography, geology, marine sciences, economics, 

geography and technology). The barriers between the conventional subject fields have disappeared 

completely. 

The student in this age range can integrate more knowledge and form more abstract concepts 

than can the primary school child. This has led to the design of units for each grade, each of 

which includes a diversity of strongly inter-related activities that cover the various fields of 

knowledge. 

For each grade, a theme acts as a core into which knowledge is systemically interwoven as 

follows: 

Grade 7: Theme: ‘We and Our Environment’ 

Unit 1 - Man and his local environment. 

Unit 2 - Variations in environmental conditions and how living things adapt to them. 

Unit 3 - Our environment is in continuous change. 

Unit 4 - Balance in the environment. 

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Qatar 

Grade 8: Theme: ‘The use and development of the natural resources in the environment’ 

Unit 1 - The various natural resources. 

Unit 2 - The use and development of renewable resources. 

Unit 3 - The use and development of finite resources. 

Unit 4 - Energy and industrialization in Qatar. 

Unit 5 - The role of machines in improving the investment of natural resources. 

Grade 9: Theme: ‘The building units and systems in the Universe, our largest environment’ 

Unit 1 - The atom is the building unit of all forms of matter; atoms form higher order systems 

of matter. 

Unit 2 - The cell is the building unit of the living organisms. Cells form systems in the living 

body. 

Unit 3 - The building units and systems in the Universe (macroscopic level). 

Unit 4 - The Universe as the principal source for energy received by the Earth. 

Within each unit there is a variety of modules inter-related together in a lattice to form the 

whole. The same is true of the group of units composing a theme for a specific grade. Each theme 

leads naturally to the next. This means children cannot do well in the second theme (grade 8) 

unless they study the first theme (grade 7). 

As an example, we now list the energy and energy related modules in each unit in grade 7. 

Examples from grade 7 

Unit 1 : 

1. Each biosystem in Qatar involves energy components in various forms; sources of energy 

in Qatar. (This is a field study module on the marine and desert biosystems.) 

2. The role of energy in defining the characteristics of a biosystem. (Heat, light, running 

water, humidity, wind . . . etc.) 

3. We explore our environment and study it through the effect of energy forms on our senses 

and our measuring equipment. (Light and vision, sound and hearing, touch, equipment for 

precise measurements of heat, light, humidity, rainfall, sea wave energy etc.) 

4. Making some thorough measurements on the energy components of both the desert and 

marine environments in the field. 

Unit 2: 

1. The energy factors (components) in any biosystem. (The nature of heat, light, and their 

role in the life cycle and on the survival of the living organisms.) 

2. Climatic and physical factors resulting from the interaction between energy and matter. 

(The role of energy in the water, carbon and wind cycles - and the role of energy changes in the 

formation of soil.) 

3. Adaptation of living organisms in a biosystem to the changes in the energy factors. (Adaptation 

to heat changes in sea and on land in the various biosystems, the range of adaptation in cold- 

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blooded and warm-blooded animals. Adaptation to light intensity, temperature and light gradients 

and their effect on forms of life.) 

Unit 3: 

1. Changes in energy in the environmental system. (Conservation of energy in any process of 

change in the environment whether natural or man-made; transformation of light energy into 

chemical energy stored in plants by photosynthesis, release of this chemical energy in various 

combustion processes - in the body of living things, in chemical reactions, etc.) 

2. Man utilizes the energy transformations for his benefit. (Some of the energy transformations 

that man utilizes for his comfort and survival such as (a) generating electricity from winds, 

water currents and waterfalls, waves, tides, (b) generating motion from burning fuels.) 

Unit 4: 

1. Matter-energy balance in the human body system, growth as a result of such balance; 

balance in the human body in ordinary activities and in such other activities as energyconsuming 

sports. 

2. Man-made technological processes and their effect on the natural balance of the environment. 

(Consuming fossil fuels, combustion by-products, how ‘these by-products pollute the 

environment. . .judging the cleanliness of several energy forms when used in industrial processes.)’ 

It wil be clear that a variety of instructional methods must be used. The children are involved 

in a variety of tasks including field trips, observation, practical work in the laboratory, information 

collection from the library or elsewhere. 

This range of experience helps to achieve such objectives of the environmental programme as: 

motivating children and developing their interest in science; training them to collect information 

using a variety of methods and so developing the concept that science is not only practised in 

the laboratory; relating children to their environment; developing in them the concepts of the 

unity of science, the unity of man and his environment; training their mental and manipulative 

skills; urging them to think and plan, to hypothesize and to test their hypotheses; helping them 

to develop environmental awareness of the many roles man plays in the environmental system, 

of its use and abuse, and of the decisions man has to take to keep God’s system running in its 

natural way, and helping them to grasp the universal laws that control the universe and its systems 

from the macroscopic to the microscopic level. 

Energy continues as an integrating theme in the secondary school curriculum which is designed 

around the separate sciences. 

TEACHING ENERGY IN THE SECONDARY SCHOOLS : GRADES 10 to 12 

I. Physics 

Energy is the core around which the physics programme for grade 10 is built. It considers the 

behaviour of the electron when it gains or loses energy and discusses the physical phenomena 

resulting from such processes. 

1. In grades 8 and 9 further energy modules are included dealing with nuclear energy, solar energy. . . etc. Details may be obtained 

from the author. 

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Qatar 

The grade 11 physics programme for science majors has as its theme: ‘Energy and matter’. It 

deals with such topics as matter and energy in nuclear reactions (fission and fusion reactions) and 

the fact that this form of energy is the origin of all other forms, i.e. it is the universal form of 

energy; the nature of radiation energy and its properties (transmission, reflection, refraction etc.) 

and the various phenomena resulting from its wave nature (diffraction, interference and polarization); 

the effect of matter on energy: wave length and velocity and the explanation of the geometrical 

phenomena in optics, and the effect of energy on matter: (a) photoelectric emission 

and the dual nature of radiation energy, and (b) the absorption of radiation energy by matter and 

the effects on its temperature, dimensions and state. 

In grade 12 we deal with the energy in a field and how it affects bodies located in the field and 

their motion. This is an attempt to arrive at a general picture of a field and its dynamics regardless 

of the nature of the field, gravitational, magnetic or electric or any combination thereof. It is an 

attempt towards the unification of physical laws. 

11. Chemistry 

The energy theme is a principal one in the study of chemistry. This article is not the place to 

discuss this in detail, but some indication of the treatment adopted may be given. Energy levels 

and sub-levels provide the approach through which the properties of elements are explained and 

categorized in the periodic table; chemical reactions are examined from the energy point of view 

and how the energy state of a reaction affects its path and its equilibrium. Separate chapters are 

devoted to the kinetics of chemical reactions, thermal chemistry and electro-chemistry. 

REFERENCES 

I 

I 

I 

I 

! 

I 

1. For statistics on education in Qatar see the annual reports published by the Ministry of Education for the 

years 1974 to 1980. Ministry of Education, P.O. Box 80, Doha (Qatar). 

2. For information on the Qatar University see the annual reports from 1972 onwards, University of Qatar, 

Doha (Qatar). 

3. GALIL, Nabil A. The Qatari Project for the Innovation of Science Education: 1st Report (1975). Doha 

(Qatar), Department of Curriculum Development, Ministry of Education, 1975. 

This report deals with the preliminary studies, the strategy of development and the plan of the project. 

4. GALIL, Nabil A. The Qatari Project for the Innovation of Science Education: Reports 2-5 (1979). Doha 

(Qatar), Department of Curriculum Development, Ministry of Education, 1979. 

These 4 reports deal with the curricula designed for: 

(1) Primary schools in Qatar 

(1-6) 

(2) Preparatory school in Qatar 

(7-9) 

(3) First year secondary (10) 

(4) Science majors 

(11 and 12) 

(5) Literature majors 

(11 and 12) 

(References 1-4 are available in both Arabic and English languages.) 

103


The problem of energy in the physics course in Soviet 

modern secondary schools 

G.A. MESYATS AND Y.B. YANKELEVITCH 

In the modern Soviet secondary school physics is taught in forms 6 to 10 (five years in all, the 

total number of class-hours amounting to 550). The teaching pre-supposes two stages of study: 

at the first stage (6th and 7th forms - 150 hours), pupils acquire a simple knowledge of the 

basic laws of mechanics, molecular physics, electromagnetism, atomic physics. At the second 

stage (8th, 9th, 10th forms - 400 hours), schoolchildren make a more detailed study of all 

parts of physics, including optics, oscillations and waves, nuclear physics. 

The problems of energy are dealt with at both stages and in almost all parts of physics. 

When studying mechanics at the first stage, the schoolchildren get the first notion about 

energy as a ‘physical value which shows what amount of work a body can perform’. They consider 

kinetic and potential energies and the transformation of one kind of energy into another. 

The explanations of such notions as internal energy (‘kinetic energy of heat movement and 

potential energy of the interaction of molcules of a body’) and temperature of a body are 

illustrated by examples. Processes causing changes of the internal energy are also considered. 

When heat phenomena are studied, much attention is paid to the laws of conservation and 

transformation of energy in mechanical and heat processes. We focus on the energy of the Sun 

which is flowing continually to the Earth and being absorbed by it. This theme facilitates a better 

understanding of the laws of conservation and transformation of different kinds of energy, 

helping the pupils to make vivid evaluations. 

The second stage of studying physics starts in the 8th form where, in the mechanics course 

(kinematics, dynamics, laws of conservation in mechanics), mechanical work and energy and the 

laws of conservation of energy are deeply and thoroughly analyzed. 

In the 9th form, children study molecular physics and thermodynamics (special attention here 

is paid to the energy of a perfect gas and the thermodynamic laws of energy conservation). In the 

section on electrodynamics and electromagnetism the energies of a charged body, of a capacitor 

and of the magnetic field are considered. 

In the 10th form, oscillations and waves are studied deeply. The transformation of one kind 

of energy into another is illustrated by harmonic oscillations (kinetic-potential). The study of 

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electric oscillations ends with the generation, transmission and use of electric power, and prospects 

for the solution of these problems are considered. The schoolchildren also get acquainted with 

optics at a fundamental level. When studying the quantum theory of light they dwell on the power 

characteristics of radiation, the processes of emission, spreading and absorption of light energy. 

In the section on atomic and nuclear physics, schoolchildren meet the fundamentals of nuclear 

energetics, with the prospect of controlled thermonuclear reactions. It wil be obvious that the 

notion of energy is the key to the whole school course of physics. Nevertheless, we think that the 

absence of a special section devoted to energy, its kinds, transformations of one kind of energy 

into another, etc., is a shortcoming of the course. It is reasonable to conclude the first stage of 

studying physics with such a section. Here one could confirm the presentation of the material 

with vivid examples and illustrations. For the pupils to learn the matefial better it is reasonable 

to make them analyze in their minds (and explain competently) the whole chain of transformations 

of the solar energy as a result of performing some concrete work. The necessity and 

possibility of the rational use of energy resources and nature conservation problems can be well 

illustrated here. 

At the second stage of mastering physics, in the section on ‘Energy’, the philosophic aspects of 

the problem must be taken into account. The characteristics and interconnection of different 

kinds of energy should be deeply and minutely generalized as was done, say, in ‘Physics for the 

Inquiring Mind’ by Professor E.M. Rogers’. 

In the 10th form a pupil can and must have a deep understanding of the definition of energy 

as ‘a universal measure of different forms of matter movement’, the transformation of one kind 

of energy into another as the transformation of one specific form of matter movement into 

another. He must be able to calculate these changes. 

We believe that, by the end of the physics course, a modern pupil could easily operate such an 

important characteristic as entropy. There is no doubt that optimal methodological ways can be 

found to provide an intelligible introduction to this material. Its mastery would promote a more 

complete and deeper understanding of the theme ‘Energy’. 

In the Soviet modern secondary school, there is no specialization; the general physics course 

is obligatory for all pupils. This is justified in the existing conditions of modern scientifictechnological 

progress, but it demands a constant search for the perfection and optimization of 

the course as a whole and of its separate parts. With the Laboratory of Physics Teaching of the 

Institute for Research on Content and Methods of Teaching (U.S.S.R. Academy of Pedagogical 

Sciences), the physics teachers in schools and colleges throughout our country are continually 

working on this problem. 

1. E.M. ROGERS, Physics for the Inquiring Mind: The Methods, Nature and Philosophy of Physical Science, Princeton, N.J., 

Princeton University Press, 1960. 

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Teaching energy in Hungarian schools: developing the 

concept over seven years 

F.J. KEDVES, L. KOV~S, P. KOVESDI 

In recent years, the concepts considered in and the didactics of science teaching have been 

recognized as providing a central problem in world-wide education. About twenty years ago, 

innovative programmes in the field of physics education were initiated in a number of countries. 

Projects such as PSSC [ 13, Nuffield [ 21 , the New South Wales (Australia) Science Programmes 

[3, 41, and the Science Curriculum Improvement Study [5] were launched. In 1968, an international 

congress on the integration of science teaching was held at Droujba, Bulgaria [ 61 which 

reflected a growing interest in the preparation of integrated science programmes for schools. 

Common to all the projects was the need to face the problems associated with the teaching of 

energy; a wide range of different solutions was proposed and tested. The present paper outlines 

the teaching approach adopted in Hungary. 

The Hungarian education system has three main divisions [7, 81. The lower division includes 

the primary schools (classes or forms 1 to 8 covering ages 6 to 13). The middle division includes 

the secondary and grammar schools (classes 1 to 4, ages 14 to 17), the training schools (three 

classes) and the extension training schools (two classes). The higher division embraces the 

universities and colleges (from three to six academic years). Children enter school at the age of 6 

and compulsory education lasts until the age of 16. The schedule of courses, curricula and most 

textbooks for the primary and secondary schools are homogeneous (and compulsory) throughout 

the country. Such a uniform system has the advantage that it makes the comprehensive planning 

of well-established science education possible. 

In 1973, the Ministry of Education invited the Hungarian Academy of Science (HAS) to work 

out and to submit recommendations concerning the future form and content of education 

programmes in the schools. Science education was to be involved in this and eventually a uniform, 

overall plan was elaborated for the twelve years of school. This work, which took four years, 

involved many scientists of various disciplines, university and college teachers as well as schoolteachers. 

Their recommendations were extensively tested in the schools and thousands of pupils 

took part. 

HAS [ 9, 10, 1 1 ] concluded that ‘from the points of view of practice, ideology and general 

living conditions, the study of science in school was as important as the studies of the mother 

tongue, mathematics or history. An understanding of science enables a person to feel at home 

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with a wide range of natural phenomena and technological processes: prediction from one’s 

knowledge becomes possible’. 

The four basic components of scientific knowledge were taken to be (1) the laws of motion, 

(2) the structure of matter, (3) the specific character of living organisms and (4) the history and 

evolution of matter. 

Five common goals were proposed for science education: to increase interest in science and to 

present science as an integral part of universal culture; to show how scientific methods may be 

used to understand nature (the fundamental steps in these methods were taken to be: observation, 

finding what is relevant to the enquiry, making theoretical models, predicting new phenomena, 

testing the models experimentally and finally applying the knowledge and understanding gained); 

to demonstrate the universal principles which are manifest in nature (which pupils should meet 

in ‘discovery’ situations and which they should be able to apply in situations which are new to 

them); to encourage children to orient themselves in the natural world using scientific methods 

based on fundamental principles (special cases being presented only as examples to be discussed 

rather than as rules to be learned); and to encourage pupils to build up a scientific world picture 

(man as the child of nature and society can transform his environment to a better one by understanding 

and using the laws of nature but not by attempting to defeat them). 

In this programme of science education, integrated science courses are planned for the first 

five classes, followed by well-co-ordinated physics, chemistry and biology. Interaction as the 

cause of all changes in nature stands at the centre of discussion. Because of the co-ordination 

between the three sciences, the conventional sequence of topics in physics was changed in order 

to help in the understanding of biology and chemistry. Thus the concept of energy was introduced 

qualitatively in class 6 through its close connection with the process of warming because the food 

chain was treated at the same time in biology. Similarly, the concept of electric charge is introduced 

in class 7 in order to help pupils to understand the chemical bond. 

The new curricula were introduced into the schools in 1978. Drawing upon the international 

experiences [ 1-61 and the recommendations of HAS, new textbooks and teachers’ guides were 

written, experimental equipment was designed for use by both teachers and pupils, audiovisual 

(AV) materials for teaching were developed and television programmes for teachers and pupils 

in primary schools were prepared. All these materials were elaborated and tested in classroom 

conditions by several dozen practising schoolteachers and university and college professors. The 

National Centre for Educational Technology co-ordinated the AV materials (colour slides, 

transparencies for overhead projectors and films). 

The examples below are representative of the development of the concept of energy from its 

connection with the process of warming to the connection between order and chance and the 

development of the Universe, finally arriving at a consideration of the energy problem in society. 

ENERGY IN THE PRIMARY SCHOOL 

Introducing science 

The discussion of the theme starts with the main topics and uses methodological principles appropriate 

to the lower primary school as part of the subject known as ‘Kornyezetismeret’ [Environmental 

Studies]. This subject, which is studied for five years, aims to develop ideas about the 

natural and social environment of the pupils. Among other topics, the three states of matter, 

interactions between elastic bodies, inelastic bodies, magnetic substances, electrified materials, 

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chemical substances, burning, simple phenomena of heat and light and the relative position and 

motion of bodies are treated. So far as the natural environment is concerned, the purpose is to 

develop the inquiring mind and to provide experience of phenomena by observation, measurement 

and experiment. The elements of physics, chemistry and biology are not treated separately 

but a generally scientific view of nature and an appropriate attitude have to be achieved. 

The teaching method is based on experience gained through individual and group activities. 

It lays the foundation of a scientific approach to the world in which the pupils live. The subject 

helps children to appreciate that the natural world can be.analysed by observation, that the 

phenomena observed have material causes and that they may be understood and increasingly 

utilized by society. 

The new Physics textbooks 

The same method characterizes the teaching of physics in classes 6 to 8 (ages 11 to 13); personal 

and group observations and experiments provide the starting point of a11 the chapters taught. 

The three texts are structured so that they support the activity of the pupils and help them to 

draw conclusions. Besides the practical activities, intellectual and logical activities are given 

greater and greater emphasis in the higher classes. The knowledge gained in this way is not only 

deeper and longer lasting than that acquired by simple ‘teaching’, but the personal activity 

introduces the pupils to the methods of research at an elementary level. 

The textbooks also reflect another important feature of the physics curriculum - namely the 

co-ordination with chemistry, biology and the earth sciences. This is in close accord with the 

proposals of the Droujba conference, although fully integrated science courses were preferred 

there for children up to the age of 13 [ 61. Co-ordinated teaching of physics, chemistry and 

biology is now possible in our schools and the new textbooks reflect this. For example, the 

concept of energy is first introduced on a largely empirical and qualitative basis; this enables 

the biologists to treat metabolism and the food chain and the chemists to develop the concept 

of the chemical bond. Co-ordination among these three subjects allows the development of an 

appropriate structure of teaching material which helps to avoid unnecessary overlap and to create 

a unified scientific view of the natural environment. 

The physics texts were written by an eight-member research group of the Teachers’ Training 

College in Szeged. The group included primary school teachers as well as college teachers; all had 

been involved in teaching experiments since 1975. On the basis of those experiments, the group 

also wrote three teachers’ handbooks, the control problems and the final tests for each class. 

They assisted in the production of the equipment required for the pupil’s experiments, the twelve 

television instructional films for each form and the AV materials. 

The content of the three textbooks [ 12, 13, 141 is characterized by the consistent assertion 

of the principle of direct interaction which was introduced in lower classes. The concept of 

energy plays a central role throughout but is most important in the sixth class because of the coordination 

with biology. As a consequence of the consistent application of the concept of direct 

interaction, the electric, magnetic and gravitational fields and their energies are also introduced. 

Interaction and field 

The treatment of interaction lays emphasis on the condition that direct contact between interacting 

bodies is necessary and that, as a result, the state of all the participating bodies wil change. 

All changes in the world are caused by interactions. Since the age of the pupils is around 1 1 years, 

the texts confine themselves (in most cases) to dealing with ‘pair-interactions’ i.e. interactions 

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between two bodies only. Building a physics teaching programme on interactions cannot hide 

the fact that, in addition to the common materials which are apparently impenetrable and 

certainly touchable, there is also ‘action at a distance’. The texts therefore go on to consider the 

magnetic, electric and gravitational fields. 

Because it is easy for the pupils to perform experiments with magnets, it is the magnetic field 

which is used to introduce the concept of field. The pupils make simple experiments with bar 

magnets and pieces of iron, noticing that the magnet can change, for example, the position and 

the motion of the piece of iron. This occurs without contact. We suggest to the pupils that the 

magnet is surrounded by a special environment which interacts with pieces of iron within it. 

We call this special environment a magnetic field. And we can recognize it only by its effects. The 

state of the magnetic field changes during its interaction with the piece of iron. This can be 

shown by the behaviour of iron filings when a piece of iron is moved through a field. The iron is 

rather like a handle with which the field can be changed. These experiences lead us to say that 

magnetic attraction and repulsion are the results of the interaction between a magnetic field and 

magnetized material. 

The concept of the electric field is similarly developed using a number of experiments. But the 

gravitational field and gravitational interaction are taught without experiment, relying on the 

analogy of the magnetic and the electric fields. To quote from the textbook: ‘The change in 

motion of a freely falling body can be explained by a field surrounding the Earth. This field is 

called a gravitational field. Its existence can be deduced only from its effects. The gravitational 

field interacts with all matter independently of its material. And the result is always an attraction’ 

[ 121. As can be seen, fields are introduced as possible partners in interactions and it is shown 

that, as in body-body interactions, body-field interactions change the states of both partners. 

Introduction to energy 

At this level, the concept of energy is developed over a series of lessons in which the pupils are 

systematically introduced to the idea. The starting point is the ability to produce change in the 

warmth of a body (‘warming capability’). It wil be noticed that this may differ in amount. 

The measure characterizing the ‘warming capability’ of a body is called energy. Bodies having 

excess energy may cause many kinds of change in other bodies. Energy, then, is a measure of the 

changing ‘warming capability’ of a body. This is a general, but qualitative ‘energy definition’. On 

the basis of their experiments the pupils recognize that, in an interaction, the energy of one 

partner increases while the energy of the other decreases. Such experiments allow us to introduce 

the idea of the conservation of energy. 

The next concept to be studied is that of ‘work’. Work is an energy change which comes about 

through the action of a force producing motion. Fields, too, have the ability to produce change 

and must also possess energy. 

Having learnt about the corpuscular structure of matter, the pupils are ready to recognize a 

corpuscular interpretation of internal energy. Heat wil be described as an internal energy change 

which takes place during thermal interactions. When the pupils formulate in words that energy 

changes can come about through the performance of work and by thermal interaction, they are 

making a statement of the first law of thermodynamics. 

It must be emphasized that the textbook speaks of energy as a measure of the ability of a body 

or of a field to act in certain ways. Thus energy is not presented as an existing, objective reality 

or its property. Pupils appreciate it as a physical concept which characterizes a capability; i.e. the 

ability for change of an objective, existing reality. 

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How energy is taught 

In the first period, examples of the ‘warming capability’ of bodies are given: a warmer body 

warms a colder one; burning oil, coal, wood or gas warms the stove; an electric heater or iron 

connected to the mains supply wil warm up; bodies in the sunshine wil be warmed; a moving 

hammer makes a nail warmer when it strikes it; a revolving wheel moved by the spring of a toy 

car can warm up a thermometer against which the wheel is allowed to rub; another thermometer 

is warmed by the body of a person and that person’s body is warmed as food is consumed. It is 

clear to the pupils that all these things have a ‘warming capability’. 

In the second period, the pupils investigate the factors on which the ‘warming capability’ of a 

body may depend. They use beakers containing 0.1 kg of water at room temperature, at 40°C 

and at 60°C and another with 0.2 kg of water at 40°C. They determine the final temperatures 

when they dip the colder and the warmer beakers into water at the intermediate temperature. 

They conclude that the larger the mass, the greater the ‘warming capability’. The teacher then 

declares that the different ‘warming capabilities’ of bodies Carl be characterized by the ‘energy’ 

and the descriptions of the observations wil be phrased in sentences using the new word ‘energy’. 

The energy of the fuel burnt is proportional to the mass and at the end of this lesson the pupils 

learn to designate different kinds of energy - elastic, kinetic, internal and chemical. 

Whether the body possessing energy can cause only a temperature rise and how the energy of 

bodies taking part in interactions changes wil be examined in the third period. Sunshine melts 

ice, heat cooks, eggs harden and some plastics soften in boiling water. A moving ball may break 

a window, the electric mains supply wil light lamps and causes electric motors to rotate. From 

such examples the pupils can conclude that bodies having energy can not only heat other bodies 

but can also cause many other changes. By analyzing the interaction of a cold body entering 

warmer surroundings, or the collision between two balls or between a hammer and a nail, discussion 

leads us to conclude that, during the interaction, the states of the interacting bodies change 

and that, whilst the energy of one body increaases, the energy of the other decreases. The energy 

gains are equal to the energy losses. These experiences lead to the concept of the function of 

state. 

In the fourth period, the pupils meet the concept of mechanical work. With the help of experiments, 

they notice that the internal energy of a body can be changed by friction. Halving a cork 

and pressing the two halves on the bulb of a thermometer whilst turning the pieces of cork round 

causes the thermometer to show a temperature rise. This is a result of friction. The pupils notice 

that when the cork turns twice, the path over which the friction acts is twice as long; the temperature 

rise is also twice as much. And so on. When the pieces of cork are pressed together more 

tightly, the temperature rise is greater for the same number of turns. The temperature rise and 

the change in the internal energy depend on the force and the frictional path. The changes can 

be calculated from the distance, s, and the force component parallel to it, F, through the relationship 

AE = F s. A change of energy always accompanies the performance of work. 

The energy of fields is studied by the pupils in the fifth period. On the basis of the observations 

that an electric field can change the state of motion of light bodies or particles and that the field 

of a rubbed plastic rod makes a small glow-discharge lamp flash as it is moved along the rod, the 

pupils readily deduce that the electric field possesses energy. However, the electric field itself 

changes as well; no light can be seen when the glow-discharge lamp is moved a second time. A 

magnetic field can change the motion of a magnet or of a moving piece of iron. The pupils have 

already seen that the motion of a piece of iron in a magnetic field wil change the field, and it 

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follows that the field itself changes while changing the motion of a piece of iron'. Assuming 

energy conservation, the pupils can deduce the energy decrease of the field from the energy 

increase of the body moving in it. The case is similar with the gravitational field.2 

The particle model for matter is used to explain the idea of internal energy. The pupils perform 

experiments in order to observe the speed of solution of sugar or a salt (e.g. potassium permanganate 

in cold and in warm water) and they conclude that the internal energy of a body depends 

on the random motion of the particles in it. The more vigorously the particles of the body move 

or vibrate, the greater the internal energy. 

In the sixth period the pupils study the concept of heat. The q.uestion is whether the same 

change of internal energy always produces the same change of temperature. We recall that the 

work done by friction on a body is equal to the increase in the internal energy. A change two 

or three times greater in internal energy is indicated by a two or three times greater change in 

temperature. Introductory pupil experiments are followed by a teacher experiment. The equipment 

consists of three similar test tubes fixed on a framework so that the bottoms of the tubes 

press against a felt turntable with the same force. The tubes contain equal masses of water, 

alcohol and mercury. The turntable is made to rotate and, as a consequence of the equal friction 

on each tube, the internal energy of the liquids increases equally. But the rises in temperature 

are very different. We conclude that the same amount of frictional work changes the temperatures 

of bodies of equal mass but of different materials differently. Now we are ready to formulate the 

concept of specific heat capacity. 

The task for the seventh period is the calculation of the change in internal energy using the 

specific heat capacity. When two bodies having different temperatures come into direct contact, 

their internal energies change without the performance of work. This interaction is called thermal 

interaction and the change in internal energy occuring in thermal interactions is known as heat. 

The pupils may finally say that the internal energy of a body can be changed both by performing 

work and by thermal interaction, thereby formulating the first law of thermodynamics. 

The course for classes 7 and 8 

The second book of this series for class 7 treats electrostatics, direct current, then hydrostatics 

and simple machines and, finally, heat engines. The concept of energy is naturally extended here 

to include electric energy and the work done in an electric field. And, during the discussion of 

simple machines, the conservation of mechanical energy plays a central role. A more quantitative 

approach to dynamics is presented in the third book (class 8). It starts by considering the conservation 

of momentum when two balls collide. A simple picture of wave motions in elastic 

systems is presented. Optical phenomena (light as the energy carrier) and electromagnetic 

induction (energy transfer using transformers) bring the primary physics course to an end at the 

age of 14. These new textbooks of physics for the primary school are based on the gradual 

development of the concept of energy. 

1. It is useful to point out repeatedly that, in the interaction between a field and a body, the body plays the role of a tool with 

which we can change both the field and its energy. If the place of a body in an interacting field changes, the structure of the field 

and its energy also change. 

2. The change in energy accompanying the work performed by lifting against the gravitational field is called in recent Hungarian 

physics books energy of interaction rather than potential energy of the lifted body. These terms are used in the grammar school; 

only in the primary school is the term change in the field energy employed. 

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ENERGY TEACHING IN THE GRAMMAR SCHOOL 

Introductory comment 

Some years ago one of us (L.K.) collected together the most important facts and ways of thought 

that might characterize the knowledge and mind of a physicist-to-be. A questionnaire was constructed 

around the most important laws and universal principles of physics. Some of those 

questions referred to fields, to energy and to everyday phenomena. We asked two classes in the 

United Kingdom which were studying Nuffield Physics and a few classes in Hungary which had 

been taught according to the traditional curriculum to answer these questions. The Hungarian 

pupils gave better answers to questions concerning relative motion but the Nuffield pupils were 

more successful in thinking about energy conservation, about fields and at finding solutions for 

the simple problems about everyday phenomena. We wished to increase the ability of Hungarian 

pupils in these areas. 

The aim was to develop a new curriculum with students’ books and teachers’ handbooks which 

would provide a better understanding of the concepts of field and energy. Our main tasks were to 

present generally applicable laws and to develop a general scientific world picture. In selecting 

experiments, we endeavoured to avoid tradition and spectacle as principles of selection. We 

agreed that experiments should not be used to prove a posteriori a relation which has been 

learned from a book or from the blackboard; the purpose of both student and teacher experiment 

must be related to discovery and the realization of their potential application. In that way, we 

can avoid a situation in which students believe that the scope of natural laws is limited to the 

classroom and the laboratory and remote from real life. Related to the primary school situation, 

teaching physics in the grammar school has two essentially new features: (i) the laws and relationships 

are always formulated mathematically as well as verbally (this implies that some formulae 

result from mathematical processes; good opportunities are provided for solving problems and for 

practising the material learned) and (ii) ‘new’ facts related to the primary school curriculum can 

be discussed. 

The approach to the teaching of energy in the grammar schools 

As mentioned already, the energy concept is developed gradually throughout the entire school 

curriculum. The introduction through the ‘warming capability’ of bodies interacting thermally 

was provided as early as class 3 (age 8). Study of th,e transfer of energy in mechanical, magnetic, 

electric and thermal interactions provides a good basis for the needs of biology and chemistry. 

The chemical transformations of materials (by e.g. burning) is treated quite early (class 3) and 

reversible and irreversible processes are also mentioned. The introduction of the idea of a corpuscular 

structure for matter comes in class 6, which allows the treatment of the energy of systems 

of many particles as the sum of the kinetic and interaction energies of those particles to be 

offered in the first year of the grammar school (age 14). 

This study of the molecular aspect of energy leads to the understanding of the aggregate states 

(solid, liquid and gaseous) of matter (connecting them with the energy scale) and allows the 

qualitative introduction of the second law of thermodynamics as reflecting the degree of disorder 

in a system. Further material concerning energy includes the idea that the internal energy of a gas 

is equal to the sum of the kinetic energies of the molecules, the equipartition of energy and the 

recognition of temperature as a measure of the average energy of the random motion for one 

degree of freedom. 

The conservation laws in mechanics are treated extensively in the second year. The pupils 

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explore rigid bodies and mechanical motion; mass; momentum (force); motion of centre of 

mass; and energy and angular momentum. 

Studies of the electron and the electromagnetic field in the third year open up the field of 

energy extensively. The richness in form of the electromagnetic field makes it possible to handle 

and transfer both energy and information with high efficiency. Students calculate the energy 

density of a coil through which a current is flowing. Then they discuss the problem of energy 

transfer from the source to the consumer. With the help of a special pair of wires (two narrow 

plates), they discuss the propagation of energy and calculate the power density mathematically 

as well as expressing it in terms of Poynting’s vector (5’): S = pi1 E B, where p, is the vacuum 

permeability and E and B are the electric and magnetic fields. 

As supplementary material, they discuss real situations as well; the wires have resistance and 

then the direction of the Poynting vector is not parallel to the wire plates. In this case, the parallel 

component characterizes the energy transported to the consumer and the perpendicular one gives 

the energy dissipated in the wire as Joule heat. 

It is in the fourth year that the features presented by the concept of energy are richest. The 

introduction of the basic concepts of statistical physics and the application of simple probability 

theory leads to a mathematical formulation of the concept of disorder and the second law of 

thermodynamics. The connection between the direction of spontaneous processes in nature and 

the minimum energy condition (valid in special cases) is also shown [ 15, 163. 

The quantum states in an atom or a molecule can be modelled by standing waves on vibrating 

strings. The wave behaviour of electrons can be demonstrated by electron diffraction, as in the 

Nuffield Advanced Physics course [ 171. The low energy modes have the simplest patterns. The 

eigenfunctions of a hydrogen atom, the formation of molecules (the delocalization of the 

electrons) and the electronic states in a metal and a semiconductor are discussed. The interaction 

of delocalized electrons leads to the development of the energy band structure as well as to the 

understanding of the presence of free electrons and the high electrical conductivity of metals [ 181. 

The treatment of nuclear physics is also based on the concept of energy. The binding energy 

per nucleon depends on both Z and N and is a maximum for elements around iron in the periodic 

table. Radioactive decay and the fusion of light nuclei show the tendency towards the energy 

minimum. Consideration of the evolution of the universe leads us from a hot system through 

hydrogen clouds to the formation of stars (building up nuclei with higher and higher atomic 

numbers) and the emergence of the planets (offering a chance for life). The energy budget plays 

a most important part in the appearance of life on Earth. And finally, at the end of the Grammar 

School Physics course, the students discuss the energy supply problems of our society both now 

and in the future. 

On the school books and laboratory books 

All four students’ books and the laboratory books have been published but have only been used 

in some twenty-five to thirty schools. So we do not yet have such extensive practical experience 

in grammar schools as teachers have in the primary schools. Looking through the books, we find 

many good ideas about the way in which students may be encouraged to discover and understand 

nature. They play, for example, simulation games with counters and dice in the first year while 

studying the internal energy of a gas and the equipartition of energy. They make patterns and 

structures with bearing balls and then they start to think about how the dependence of the interaction 

energy of the particles depends on the distances of the first and second neighbours. In the 

second year, a number of collision experiments are done by the students with pucks on an air 

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table (using stroboscopic pictures for evaluation), with vehicles on a linear air track (using photodiodes 

and an electronic counter for measuring the time) or with trolleys on a low friction track 

to which is applied a simple electrostatic method for time measurement (using powdered sulphur 

and the mains supply). 

The pupils are searching for conserved, unchanging quantities and so find the idea of momentum 

(from which they get Newton’s second and third laws). In the case of elastic collisions, they 

discover ‘the conservation of the square of the velocity’ of trolleys, and so get a feel for the 

concept of kinetic energy. In the fourth year, the exercises introducing statistical physics begin 

with the throwing of dice in a way which is rather similar to that described in the Nuffield 

Advanced Physics Unit 9 (Change and Chance) [ I5 I . From statistical physics the Hungarian 

curriculum goes on to use the energy point of view in both nuclear physics and astronomy, so 

achieving a unity of pedagogical treatment. The extended use of a three-dimensional model 

for the nuclear binding energy helps when considering the energy budget of the universe. This 

model effectively demonstrates that during radioactive decay and during stellar evolution, the 

cosmic matter ‘flows into the ferrum lake’ because the ‘energy valley’ around iron in the periodic 

table is the deepest, so offering the most stable state. 

CONCLUSION 

In the last century physicists believed that school physics was a condensed form of complete 

physics. The information explosion of the present century has rendered this belief pedagogically 

absurd. One has to select a unifying standpoint from which one can educate students to 

develop precise thinking about the world we live in. In the traditional school physics curriculum, 

the favoured central concept was that of force (measured by springs). That concept has one great 

disadvantage, however; in Physics, outside Newtonian mechanics, its value is low and it is almost 

useless in modern chemistry and biology. The ‘chemical force’ (valence) and ‘vis vitalis’ mean 

something completely different. So a force-centred physics curriculum results in the isolation of 

our subject from the other sciences. The new Hungarian physics curriculum is energy-centred, 

energy being taken to include internal energy and light energy from the very beginning. This 

central role for energy places heavy emphasis on thermodynamics, electric energy transfer, the 

ground states of atoms and crystals, stellar evolution and human energy resources; it opens doors 

to chemistry, biology and economics. Using it, we shall be able to present physics as a subject of 

real relevance to all men and women. 

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REFERENCES 

Hungary 

1. HABER-SCHAIM, U. The PSSC Course. Physics Today. March 1967, pp. 26-31. 

2. ROGERS, E.M. The Nuffield Project. Physics Today. March 1967, pp. 40-5. Nuffield Projects relevant to 

this paper include Nuffield Combined Science for ages 11-1 3, Nuffield Secondary Science for ages 14-16, 

Nuffield Physics for ages 11-16 and Nuffield Advanced Physics for ages 17-18.lst ed., London, Longman, 

1967-72. 

3. MESSEL, H. (ed.). Science for High School Students I, II. Sydney, (Australia), The Nuclear Research Foundation, 

The University of Sydney, 1964. 

4. MESSEL, H. (ed.). Senior Science for High School Students, 1. Physics, 2. Chemistry, 3. Biology. Sydney 

(Australia), The Nuclear Research Foundation, The University of Sydney, 1966. 

5. Several programmes of the Science Curriculum Improvement Study, 1971, Berkeley, Calif. 

6. Congress on the Integration of Science Teaching, Droujba (Bulgaria). Paris, CIES, 1968. 

7. Public Education in Hungary. Budapest, Ministry of Education, 1973. 

8. Hungarian Education in TermsofFigures 1978-1979. Budapest, Ministry of Education, 1979. 

9. MARX, G.; KEDVES, F.J. Teaching of Science in Primary and Grammar School. Budapest, MTS (Hungarian 

Academy of Sciences), 1974. (Draft - in Hungarian.) 

10. Attitudes and Recommendations of the Hungarian Academy of Sciences on the Content of Future Culture 

and the Development of Educational Activity in Schools. Budapest, MTA (Hungarian Academy of Sciences), 

1973-76. 

11. MARX, G. Science Education in Hungary. Budapest, Department of Atomic Physics, R. Eotvos University, 

1977. 

12. KOVESDI, P.; BOR, P.; HALASZ, T.; KovAcs, L.; MISKOLCZI, I. Fizika 6. Budapest, TankAnyvkiad6,1978, 

and Szeged, JGyTF, 1980. 

13. KOVESDI, P.; BOR, P.; HALASZ, T.; KovAcs, L.; SZANTO, L. Fizika 7. Budapest, Tank;nyvkiad6,1979. 

14. KOVESDI, P.; BONIFERT, K.; HALASZ, T.; MISKOLCZI, I.; SZANT~, L. Fizika 8. Budapest, TankAnyvkiad6, 

1980. 

15. OGBORN, J.M., et al. Nuffield Advanced Physics Unit 9. Change and Chance. London, Penguin/Longman, 

1972. 

16. MAW, G.; T6TH, E. Energie und Ordnung. Sammelband Leitthemen - Beitrage zur Didaktik der Naturwissenschaften 

und Mathematik (Koln), Aulis Verlag (in the press). 

OGBORN, J.M. The Second Law of Thermodynamics. School Science Review (London),Vol.57, No. 201, 

1976, pp. 654-72. 

MARX, G. Interface Physics-Biology , European Journal of Science Education, 1980. 

17. OGBORN, J.M. Introducing Quantum Physics. In: Unesco, New Trends in Physics Teaching, Vol. 11, Paris, 

Unesco, 1972, pp. 81-103. 

18. KEDVES, F.; KOVAcS, L. Concept of Solids in Physics Curriculum, Structure of Matter in the School, 

pp. 149-55. Budapest, R. Eotvos Society, 1979. 

KEDVES, F.J.; KOVAcS, L. Analogieversuche zum Energie-Bandermodell der Festkorper, Physik in der 

Schule (Berlin), Vol. 13,273,1975. 

115


An experience in the teaching of energy in Italy 

A. BASTAI PRAT. 

ENERGY, SCIENCE AND SOCIETY 

In recent years Italian physics teachers have taken a great interest in ‘Science and Society’ themes, 

particularly in that of energy. This interest, however, has rarely given birth to systematic teaching. 

This is due mainly to the structure of our schools, which is in principle very rigid and centralized, 

with programmes and timetables, fixed at the national level, which, at least, for upper secondary 

schools, are very old, obsolete and give little time for science teaching. However, Italy is a country 

of individualists, and what is not allowed in principle is often done in fact. So, many teachers, 

driven by their students’ requests or by their own feeling of the importance of the matter, have 

introduced this theme into their courses more or less officially. 

It would be very difficult to give an overall view of these attempts, since they have been on 

small scale, without comparing the results. For instance, in Torino students from one school 

collected data on energy consumption from a sample of over 3,000 families, constructing data 

tables and analyzing them with a computer [ 11 ; in other schools students designed and built 

solar panels on the roof of the building, and in a country school they even built a working 

digestor to produce energy from organic wastes [ 21. 

Here I shall describe what our own group - an informal group of university and secondary 

school teachers - has done in recent years. Interest in our experience, if any, may lie in the fact 

that we tried to connect together various experiences and to make the results available to a larger 

audience, through printed commercial materials, informal distribution of preliminary versions 

through professional associations, in-service teacher training courses, and so on. 

THE ENERGY PROBLEM: AN HISTORICAL APPROACH 

Our interest in the energy problem began in the period when some of us [3] were working on the 

Italian adaptation of the Project Physics Course. In this course, the energy concept is introduced 

and immediately followed by a discussion of the steam engine and its impact on the industrial 

revolution; this in turn leads to the discussion of the equivalence between heat and work. 

116

Italy 

This approach proved interesting and stimulating for teachers and students: the relevance of 

the energy concept, and of conservation of energy as a great unifying principle seemed to emerge 

much better from such an historical picture than from the treatment usually presented in physics 

courses. 

Other materials on the same line were published independently from Project Physics, by Italian 

authors [4]. These are not really textbooks, but rather subsidiary teaching materials, to be read 

and discussed after a normal physics course, or by groups of brighter pupils. Nevertheless, even 

if they correspond more to a social science or history of science course, they have had a noticeable 

influence on many physics teachers. 

In fact, it is very difficult to reach an equilibrium between the ‘Science’ and ‘Society’ components 

of such courses; in the usual physics courses, there are some notes on the social relevance 

of scientific discoveries, but these are very superficial and often inaccurate. If the social aspect of 

science is stressed more deeply, there is the danger that the course tends to be based on the ‘ideas’ 

of science, and not on science itself, with its experimental and mathematical components. This is 

a particular danger in a country like Italy, where teachers are not inclined to teach through 

experiments, and prefer chalk-and-talk methods. 

Therefore it seemed worthwhile to try to develop a teaching approach to the energy concept 

that followed the way it emerged in the nineteenth century and which connected it to today’s 

energy problem. This possibility was discussed, somewhat confusedly at the beginning, in our 

group, in teacher-training courses organized with biology and chemistry teachers and in some 

graduate theses. The following pattern finally emerged: 

(I) An introduction to thermodynamics which followed the historical development, and 

which showed the connection between the discovery of the laws of thermodynamics and the 

process of industrialization. 

(11) A series of short optional units on some present aspects of the energy problem, to be used 

in connection with a traditional physics course. 

In this paper, the first part of this pattern wil be outlined briefly, while the second wil be dealt 

with in more detail. 

THE APPROACH TO THERMODYNAMICS 

(a) In the first phase (eighteenth century), the fundamental concepts of temperature and 

heat were developed and distinguished, and adequate measuring apparatus was built. This was 

mainly done by ‘natural philosophers’ (or, in the language of to-day, ‘pure scientists’) and forms 

the bulk of calorimetry. 

(b) Technical problems in the field of newborn industries led to the concept of work; the 

discovery and improvement of the steam engine led to the idea of a connection between the heat 

given to a thermal engine and the work produced by it, and to the concept of efficiency. This 

was mainly due to Carnot and it leads to the second law of thermodynamics, in the form of a 

maximum limit to the efficiency of any device that produces work by receiving heat. 

(c) In a third phase, mainly due to Joule and Helmholtz, the so-called equivalence between 

heat and work and the law of conservation of energy were established. This law appears as a 

universal principle, connecting together such different fields of science as physics, chemistry, 

biology, engineering, and so on. When connected with Carnot’s principle, it gave birth to the 

science of thermodynamics. 

117


(d) In a fourth phase, the laws of thermodynamics were ‘explained’ by the kinetic theory, 

removing the idea of a basic difference between the sciences of heat and of mechanics, and 

introducing the ideas of the atomic structure of matter and statistical laws. This opened the 

way to the fundamental problems of moderh physics. At the same time thermodynamics was 

applied to new industrial fields and the distinction between pure and applied science was firmly 

established. 

An introductory thermodynamics course (age 16/ 18), presenting the physics of the subject 

in the succession through which it was built, deals with each of these four phases in turn. This 

approach [ 51 , developed through two graduate theses and informal trials in classrooms, has just 

been published. 

The pattern shows the two-way connection between science and social problems: not only 

how science is applied to the solution of industrial problems, but also how the development of 

science is conditioned by external requirements and fostered by problems that arise outside the 

‘pure science’ field. In fact, applied science was born only in the early years of the nineteenth 

century; before that the contribution to scientific development given by the industrial revolution 

was more important than the help it received from contemporary science. Today we are 

confronted with a similar situation in a different field: informatics was born for technological 

reasons, but it is changing the way ‘pure science’ is done and opening new fields of research. This 

may be of interest to students, particularly for those who do not intend to become scientists, 

but who may need, in their place of work, to take into account the possibilities and the limits of 

scientific solutions to social problems. 

On the other hand, this historical approach is closely connected to the inquiry approach: if 

science is research, and if students feel that their learning is, in some way, an investigational 

process, then it is natural to discuss the way in which the actual research and discovery process 

happened. It is hoped that it may also help teachers to develop a different attitude. In Italy, 

most teachers are afraid of introducing inquG lab work into their classroom and tend to teach 

as they were taught, mainly by chalk and talk and possibly by routine experiments. Many of 

them are mathematics graduates and have never been trained in laboratory work; in any case, 

they were trained to believe that experiments must always lead to a well defined result, as stated 

in a textbook or worksheet. It is possible that an historical approach, with its record of trials and 

failures and patient search for better equipment and better mathematics and better theories, can 

encourage such teachers to try different open-ended lab work. In this case it would be very useful 

to develop an appropriate set of historical experiments. 

Another reason for this approach is that it tries to separate the different contributions which 

make up the science of thermodynamics. Calorimetry, the oldest part, still uses terms coming 

from the caloric theory (‘latent heat’ is a typical instance). Then there is macroscopic thermodynamics, 

which makes forecasts based on very general rules (at this level the zeroth, first and 

second laws). These rules are accepted without explanation, because they are supported by 

experimental evidence and lead to correct forecasts, just as the universal gravitation law is accepted 

on similar grounds, without ‘inventing hypotheses’ to justify it. On the other hand, after discarding 

caloric theory, the search for an explanation led to kinetic theory and to the statistical 

interpretation of thermodynamics. Mixing the various approaches leads to well known confusions, 

such as that between heat, internal energy and kinetic molecular energy (and temperature). It is 

hoped that the historical approach can help understanding, by showing the contexts in which 

different frameworks have grown. 

118

Italy 

ENERGY PROBLEM: TO-DAY'S ISSUES 

In our time, energy production, distribution and use is again - after a period of abundance and 

low cost - a crucial economic problem. The same industrial society that was started by the 

invention of energy-producing devices and developed by substituting mechanical energy for 

human work is now threatened by energy shortage; and the science that was born in the industrial 

revolution is asked to find a way for survival. 

This issue is particularly important in Italy, where local energy resources are very scarce. 

Hydro-electric power, mainly available in the Alpine region, has been heavily exploited already. 

The country is now dependent on imported energy (mainly oil) for more than 75 per cent of 

consumption. An intensive nuclear plant building plan was proposed some years ago, but, as in 

many other countries, it met with strong opposition, particularly from people who lived near 

planned reactor sites. Solar technology, which in our geographical position could make an 

important contribution, is not sufficiently developed, nor is it supported by the government. 

In such conditions it seems very important that students are informed about energy technologies 

and resources, and about methods of decision-making in this field. This is also a way to introduce 

some important physical concepts and applications into the curriculum. 

However, as has already been mentioned, the structure and organization of the Italian school 

system makes it very difficult to devote much time to a subject not already included in the 

official programme. Relevant modifications are possible only if an authorization is requested of 

the Department of Education, with many bureaucratic complications. Moreover, examiners are 

not prepared to deal with such abnormal situations, and this may cause damage to pupils who 

receive lower marks than those following the conventional course. 

So our group chose to develop a set of short units, requiring about ten periods each, for the 

16 to 19 age range, that could be inserted into a normal physics course at different stages. Some 

units need very little preliminary physics and can be used at the beginning of the course or by the 

mathematics teacher (who in Italy is very often the physics teacher as well); some units can be 

used before electromagnetism is dealt with, and some only at the end of the course. 

This flexible proposal also came about for another reason: one of our primary aims - as is 

apparent from the first part of this paper - is to help to change the way the energy concept is 

taught from its first introduction in the curriculum, and not merely to change a final chapter 

in a standard physics course. We feel that the energy conservation law, which connects quantitatively 

many different fields of science, should be introduced by a wide variety of different 

examples. For instance, mechanical energy is usually introduced by considering classical machines, 

levers and pulleys and so on; wind and tidal generators could be additional examples, attractive 

to the students. 

Obviously this choice poses various problems, because we must try to make the units as 

independent as possible from each other, and at the same time avoid unnecessary repetition. 

The scheme of units is as follows: 

Part I: Limits of growth 

(a) Trends in energy consumption 

(b) World energy resources 

Part 11: New methods of energy production 

(a) Nuclear fission reactors 

(b) Nuclear fusion 

(c) Renewable resources 

119


Part 111: Problems of energy distribution 

(a) Electrical energy networks 

(b) Coal gasification and liquefaction (Hydrogen as vector) 

Part IV: Final uses 

(a) CO-generation and heat pumps 

(b) Domestic uses of energy 

It must be noticed that this is not a list of titles, but of the main contents of each unit. It is a 

preliminary scheme, and wil probably change before it reaches its final form. For instance, it is 

very likely that the nuclear units require a separate short introduction on nuclear structure and 

that the ‘Renewable resources’ unit wil split in two, one unit on mechanical energy (winds, 

tidal, waves) and one on solar energy, to be placed later in the curriculum. 

The first unit, ‘Trends in Energy Consumption’ has been presented at the Conference of the 

Italian Association of Physics Teachers, and a hundred or more copies have been distributed and 

were scheduled for trial in schools in 1980-81. Some quite favourable reports have already 

come back. 

Other units are taking form, in the sense that a preliminary draft has been established and 

discussed: these are the two nuclear energy units, the ‘Domestic uses of energy’ and the ‘Energy 

resources’ units. Some parts of these have already been tried in the classroom situation. The 

whole scheme should be completed next year. Financial support has been obtained by the 

National Committee for Research (CNR) and this should allow more systematic trials. 

Energy consumption and resources 

The main problem in these units was to avoid giving simply a list of data, which would have been 

of little educational use, probably boring, and in any case already available in books, newspapers, 

etc. So we set down the following list of objectives for the ‘Energy Consumption’ unit [ 61 : 

Pupils should be able (a) to understand and use various types of graphs, to translate tables of 

data into graphical form and vice versa; (b) to understand the importance of reliable sources for 

data, and to know the most important international agencies in the field (the United Nations 

Organizations, the International Energy Agency (IEA) and OECD) and their function; to understand 

the necessity and difficulty of establishing standard units for energy consumption; (c) to 

understand and apply (in simple contexts) economic indicators relevant to the problem, such as 

GNP, per capita quantities, elasticity coefficients’ and so on; (d) to understand the relevance of 

general economic conditions of a country in determining its energy consumption, and the choice 

of the energy sources; (e) to understand the main assumptions on which medium and long term 

forecasts (or ‘scenarios’) are built, and to be aware of the difference between factual and political 

assumptions; and (f) to make simple exponential calculations, using a pocket calculator, based 

on various growth assumptions. 

The unit is divided into four parts: 

(1) Energy and economic growth. An introduction in which standard units (tonnes of oil 

1. Economists frequently use the term elasticity when describing the ratio of two related rates of change - for example, the 

ratio percentage change in a demand is known as the price elasticity of demand. Here the term refers to the 

percentage change in price 

ratio percentage change in energy consumption 

percentage change in gross national product. 

120

Italy 

equivalent or t.0.e.) are defined, and the relationship between GNP and energy consumption is 

discussed. For instance, students are asked to compare and discuss the two diagrams shown in 

figures la and lb (deliberately drawn with different techniques) and to derive information 

about energy consumption in various countries (aims (a), (c) and (d). 

A 

200 - 

Africa 

S.America 

Asia 

m, 

-3 

0 

r 

\ 

(I 

.- 

0 

4J 

? 

3 10 

m C 

0 

U 

U.S.S.R. & 

E. Europe 

W. Europe 

2o t 

I I I 

1950 1960 1970 

Figure la. Growth in energy consumption, 1950 to 1970. 

N.America 

Figure lb. World populations, 1970. 

121


It is shown that for the period between 1960 and 1973 elasticity coefficients (rate of growth of 

energy consumption/rate of growth of GNP) were about uriity in industrial countries. 

(2) The years of expansion. The data for energy consumption and of its growth in the years 

1960 to 1973 are discussed in more detail, taking into account the trends of consumptions for 

various energy sources. Students are warned against misleading graphs: for instance, the two 

graphs (figures 2a, b) report exactly the same data, but convey a very different impression. 

100% rn 

I 

m 

U 

U 

Lc 

0 

8 50%-% 

o_ 

a 

C 

Coal 

' Others 

I 

0% I 

1953 1963 1970 

Figure 2a, b. Alternative presentations of the statistics of the changes in energy consumption, 1950 to 1970. 

122

An obvious question arises: why did European countries, with their limited energy resources, 

accept a form of growth that would lead most of them to depend so heavily on foreign supply? 

The answer is obtained by quoting and discussing various OECD policy statements, which assume 

as a matter of fact that the commercial and political supremacy of European countries wil 

permit them to obtain at low cost, growing energy imports (this is an example of discussion 

relating to objective (e). This fundamental assumption has proved wrong during the last decade. 

(3) Actual situation. In this section, the post-1973 situation is discussed, by comparing data 

on various scales: World, Europe, Italy. Another example of a misleading graph, of different 

origin from those seen before, may be of interest, (see figures 3a, b). 

30 

- 

Pr ce of Arabian Light 0 I [doilar/berrel I 

Italy 

26 0 

20 

- 

- 

0 

L 0 - 

n 

\ . 

10 

- r‘ 

r 

I 

1971 1 9 7 2 1 9 7 3 1974 1975 1976 1977 1976 1979 I980 

F g 3a 

110 

- 

/ 

/ 

I 

70 

60 

50 

- 

- 

- 

Figure 3a, b. Alternative presentations of the price of Arabian light oil, 1971 to 1980. 

123


(4) How to build a ‘Scenario’. This section starts with an assumption that is discussed later: 

that both the rate of increase of GNP and the coefficient of elasticity (see footnote above) 

can be considered approximately constant. This leads immediately to exponential growth, which 

is presented here in a very elementary way, as a geometric increase. It is very easy to derive the 

formula: 

C, = (1 +k), CO 

where CO = initial consumption, Cn = consumption after n years, k = yearly rate of growth, as a 

fraction of total consumption. Possible values of k are taken from IEA (1980) data and the 

students are informed that these are official data, on which international policies are based. They 

are also warned that the use of such data for long term forecasts does not make much sense, but 

it can be useful in order to see what would happen if nothing changes (this is the concept of this 

scenario). They calculate data up to year 2000, and if they wish they can try other values for k. 

Then they compare the figures with the actual proven oil reserves, and the proven oil plus coal 

reserves. To evaluate the total consumption over the whole period, additional mathematics is 

needed (essentially the formula for the sum of a finite geometric series which can be derived 

without difficulty or accepted as ‘black box’ formula). 

For calculations, various possibilities are suggested: since programmable calculators are not 

usually available, the best choices are calculators with yx keystroke, or the use of logarithmic 

paper. The use of a plain arithmetic calculator alone proved feasible but rather boring. 

This part of the work is, in practice, quite exciting and students are astonished to see how little 

difference in the exhaustion time is caused by a different estimate of reserves, as long as we 

accept the exponential growth assumption. (See also pp. 20-37 above.) 

The conclusion is that there are two possibilities: either new reserves, in unlimited quantity, 

are made available, or the growth of energy consumption must slow down. This can be done by 

limiting the growth of GNP (zero growth model) or by decreasing the elasticity coefficient, that 

is, by using less energy for the same production (economy of energy). It is suggested that all these 

possibilities should be explored at the same time, and that no one of them alone can solve the 

problem. 

The second unit, ‘Energy Resources’, should not become a summary of information. What we 

try to do is to give an idea of how data about energy reserves and resources are established, and 

underline the fact that they are by no means fixed quantities. The contents of this unit can be 

summarized as follows: (a) Definition of energy ‘reserves’ and ‘resources’: how much can be 

recovered, under what conditions, at what cost? (b) Some indications about the way resources 

are estimated: the geology of fossil resources. (c) Actual and past data about energy reserves 

and resources. (d) Energy content of resources: the connection between technological choices 

and energy content of resources. In this unit, we deal mainly with fossil resources: renewable 

resources are discussed in another unit. 

Nuclear energy 

While the units on energy consumption and resources introduce few energy concepts - the 

problems related to final uses and therefore to conversion efficiency are dealt with in other units 

- the two ‘nuclear energy’ units introduce many relevant ideas in physics. 

The aims of both units can be summarized as follows. Students should learn to: (a) apply in a 

new context some important ideas of classical physics (e.g. apply the kinetic theory of gases and 

124

knowledge of electromagnetism to the discussion of plasma confinement); (b) understand some 

general features of nuclear structure and nuclear forces (no preliminary knowledge is assumed); 

(c) understand the basic features of chain reactions and the way they are controlled; (d) apply 

basic physical concepts in order to understand the design of nuclear reactors; and (e) understand 

and apply the basic techniques in the discussion of safety requirements (e.g. the ‘probability tree’ 

and, if space allows, the Harrisburg incident as a case study) and the waste-disposal problem. 

We feel that, since the nuclear fission energy problem is so hotly debated, authors must state 

clearly their personal position at the beginning of the unit, in order not to influence covertly 

teachers and students. Our position is - on the whole, and with some disagreement in the authors’ 

group itself - a moderate pro-nuclear one. But we are, in any case, firmly convinced that two 

attitudes must be avoided: one is the ‘don’t disturb the experts’ position. People must insist on 

being informed and must try to understand as far as possible the technical and political issues 

and the reasons on which decisions are taken. The second negative positionis the ‘atom is the 

devil’ attitude: we intend to stress that atomic technology is quite well known and can be understood 

by the layman as much - or as little - as any other technology. Risks can be evaluated, 

just as in any other field, without absolute certainty and withoat total obscurity, and we must 

choose whether we want to run them, or to pay the price for avoiding them. It is probably true 

that the atomic choice is part of a general ‘hard’ technological choice and that this may in the 

long run lead to disaster; it is also probably true that people’s habits and the social structure cannot 

change in a few years, and that in countries like Italy, with little or no local resources, fission 

reactors can usefully smooth out the transition to the next generation of energy technologies. 

A long description of the two units would be out of place here, and moreover they are not 

yet complete; but it is possible to give an idea of some features that have proved interesting 

during discussions of the preliminary drafts and classroom trials. 

The nuclear fission unit [7] requires an introduction on nuclear structure (whether or not it 

must become a separate unit is under discussion). The problem is introduced by the question: 

what can we measure about nuclei? The answer is that we can measure very little; only radius 

and mass, if we don’t want to consider very sophisticated experiments. Rutherford’s experiment 

(as a model for scattering experiments) and a mass spectrograph are sketched. Knowledge 

of mass leads to knowledge about energy (E = mc2 wil probably remain a ‘black box’) and we 

can draw a curve of binding energy per nucleon, using experimental data. From the curve, we 

may derive the main characteristics of nuclear forces. The first feature we notice is saturation, 

i.e. binding energy per nucleon grows to a maximum, then decreases slowly. This means that 

nuclear forces are short range: each nucleon interacts only with its nearest neighbours, and is 

not influenced by the addition of other nucleons outside the interaction range. Coulomb repulsion 

then accounts for the decrease in binding energy at the top of the periodic table. The exclusion 

principle (already known from atomic structure) accounts for the fact that the number of 

neutrons cannot be too high for a given 2; this provides us with a relevant insight about elementary 

particles, namely that neutrons and protons are identical so far as nuclear forces are concerned. 

Then there are minor corrections, such as magic numbers, parity effects, surface effects, giving 

supplementary information. 

Another point that proved interesting during classroom trials was the general pattern of fission 

reactor design. Once students have understood how fission is controlled, they can draw a list of 

possible fissile materials and possible moderators and try to match them. They immediately see 

that a poor fissile material, such as natural Uranium, requires a moderator which is a poor 

absorber, such as heavy water; if we enrich the fuel, we can use a less sophisticated moderator, 

such as natural water, and so on. 

We were quite pessimistic about nuclear fusion, considering it a very complicated subject: 

Italy 

125


magnetohydrodynamics is not the sort of thing that is considered fit for simple illustration. On 

the other hand we were pleased to discover that it offers some nice applications of introductory 

electromagnetism, on a semi-quantitative basis. It may be of interest to look at some examples. 

In the usual physics course, students discuss the motion of a charged particle in a uniform 

magnetic field. The discussion of plasma confinement requires them to consider a non-uniform 

field. 

We consider two possibilities: field intensity may either vary across the magnetic field lines, 

or along them. 

The first case occurs in such toroidal devices as Tokamaks, as simple reasoning based on the 

circuital law shows at once (figure 4(a). Let us consider an electron moving in a plane normal 

to the field lines (in figure 4(b) B lines cross the page at points indicated by dots). The field B 

is normal to the paper, directed away from the reader, and it is stronger in the lower part of the 

diagram. The electron path wil have two different radii of curvature, and it is apparent from the 

diagram that this wil lead to an open trajectory, drifting towards the right. This is the main 

reason why a simple toroidal field cannot provide plasma confinement. Another field must be 

superposed on it. 

TOROID‘AL FIELD: internal fieldlines 

being shorter, must correspond to 

higher B values. 

t b3 

......... 

......... 

I C3 

___) 

... vdrift 

................. 

................. 

‘current 

Figure 4. 

The second case is typical of ‘mirror’ devices, (figure 4c) where the field lines converge at the 

two ends of the device. Let us consider a charged particle arriving from the left, spiralling along 

the magnetic field line. It can be considered as a current loop, travelling towards a region of 

increasing magnetic field. As the number of the magnetic field lines crossing the loop increases, 

an e.m.f. increases the current in the loop which generates a current that slows down the loop 

and eventually reflects it back. This is a very well known fact (eddy currents in a moving conductor) 

and every physics laboratory has devices to illustrate it. 

126

Naturally not all the particles are stopped by the ‘mirrors’, depending on the initial speed and 

direction: there is therefore a ‘loss cone’ from which particles can escape. 

Italy 

Such elementary reasoning - that can be used in a more quantitative way - naturally doesn’t 

apply when we go over to collective plasma motions, that is, to magnetohydrodynamic instabilities. 

In that case the simple approximation of one particle moving independently in a given 

magnetic field breaks down, as there are finite lumps of plasma modifying, with their motion, 

the field they are moving in, and this corresponds to a non-linear problem. 

Another example of the approach we are looking for is the analogy between an internal 

combustion engine (figure Sa) and a laser fusion device (figure 5b). 

fuel injection compression ignition cam 

combustion 

Figure 5a. Internal combustion engine. 

fuel pellet 

injection 

compressior 1 ignition 

[by laser I [by laser1 

thermonuclear 

combustion 

‘coolant 

Figure 5b. Laser fusion engine [ 101 

The analogy immediately draws the attention to some typical problems: the combustion 

process must be as complete as possible and therefore the combustion (= ignition) time must be 

smaller than the time taken by the pellet to explode, and compression must be completed before 

ignition begins. And in both cases there must be an efficient method of taking away and converting 

the energy released, 

Other units 

Of the other units, the only ones that are taking form at this time are the ‘Final Uses’ units. 

These introduce an important theme, the ‘economy of energy’, and allow the development of 

some relevant physics concepts, usually not dealt with in standard courses. 

127


‘Domestic uses of energy’ deals, of course, with two main themes: electricity and heating. It is 

intended to be a bridge between the everyday experience of pupils and what they learn in physics 

courses, and between the large scale energy problem and the personal decisions of each citizen. 

Apart from a number of well known laboratory experiments about circuits, power spent in home 

appliances, heat conduction, and so on, we feel that a very nice approach to home heating is the 

simulation game [8] used in the Association for Science Education (ASE)‘Science in Society’ 

course. Some of our group translated the materials and tried them with Italian students, with 

quite good results [9]. There is however a problem of time and of adaptation to the Italian 

situation. 

The other unit deals mainly with the distinction between the different ‘values’ of energy forms, 

according to the second law of thermodynamics: high temperature and low temperature heat, 

mechanical and electrical energy. An interesting Italian example of the high efficiency use of 

energy is provided by TOTEM (Total Energy Module), produced by Fiat: a car engine (Fiat 127) 

has been adapted to produce electrical energy and heating. 

However, there are various difficulties, mainly related to ethe fact that electrical energy and 

heating are not required at the same time. There is the need to transfer electrical energy to the 

general network when it is not used, and to receive energy when TOTEM is not adequate; but 

connecting such devices to the general energy network poses problems (particularly if they are in 

large number) and the diffusion of this scheme wil depend on the attitude and support of the 

authorities. 

REFERENCES 

1. Liceo Einstein. Inchiesta sugli usifinali dell’energia. Torino, 1981. 

2. BONI, E.; MAYER, M. La dimensione progettuale nella scuola, una proposta sulle energie alternative sperimentata 

a1 Liceo Sarpi diRoma. Communication to the AIF Conference, Formia, 1980. 

JANNAMORELLI, B. Impianto per la produzione di biogas. Communication to the AIF Conference, Formia, 

1980. 

3. The Project Physics Course. Italian translation and adaptation by A. BASTAI PRAT, B. QUASSIATI, G. SALIO, 

G. STEPANCICH and L. VIGLIETTA. Bologna, Zanichelli, 1977. 

4. BARACCA, A.; LIVI, R. Natura e Storia - Fisica e sviluppo del capitalismo ne11 ’Ottocento. Firenze, D’Anna, 

1976. 

MAFFIOLI, C. Una strana scienza - Materiali per una storia critica della termodinamica. Milano, Feltrinelli, 

1979. 

BARACCA, A.; RUFFO, S.; RUSSO, A. Scienza e Industria 1848-1915. Bari, Laterza, 1979. 

5. FERRATO , P.; MESSIDORO , M.T. An Historical Approach to Thermodynamics. Graduate thesis, University 

of Torino, 1978. 

BASTA1 PRAT , A. Calore, materia e moto - DaZ concetto di temperatura alla meccanica degli atomi. Bologna, 

Zanichelli, 1981. 

5. BASTAI PRAT, A.; VERDEU VEcco, G. Materiali didattici sul problema dei consumi di energia. Communication 

to the AIF Conference, Formia, 1981. 

7. RAMELLO, M.L. Introduzione didattica a1 problema della fissione nucleare. Graduate thesis, University of 

Torino, 1978. 

8. ELLINGTON, H. Central Heating Project Pack. HatfieId, Association for Science Education (ASE), Science 

in Society Project, 1980. 

9. BRUNATTI, B.; QUASSIATI, B.; VIGLIETTA, L. Un ’esperienza sull’uso della giocosimulazione come strumento 

didattico. La Fisica nella Scuola. 1981. 

10. After DUDERSTADT, D.E. Nuclear Power. New York, Marcel Dekker, Inc. 1979. 

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Senegal 

Reflection on current trends in physics teaching in upper 

secondary education and the first years of university 

education in Senegal: the teaching of the concepts of energy, 

entropy and irreversibility 

D. FALL. 

A survey conducted among teachers and other education personnel in Africa would reveal that 

pupils encounter three major difficulties in assimilating certain physics concepts: first, the 

expression of these concepts in a foreign tongue; second, the lack of material facilities for the 

experiments which so often serve as an indispensable means of illustrating them; and third, the 

teaching methods which often lead the pupil to recite set formulae and even to describe experiments 

without having really understood the physical reality to which they refer, the meaning of 

the words used or the formulae quoted. 

In the case of Senegal, efforts have been made in the last few years to improve such teaching 

and an experiment is being carried out in pilot schools where new physics courses are taught in 

the sixth form. A good start must be made if pupils are not to go on to university still suffering 

from inadequacies. 

The present paper is mainly concerned with this sixth-form course and with the steps that 

should then be taken to ensure some continuity in this teaching thereafter, with particular 

reference to university education (first and second years). 

THE CONCEPT OF ENERGY 

The concept of energy is gradually built up on the basis of the concept of the capacity for work 

of a force, with reference to experiments involving the operation of simple and easily constructed 

machines: the slow fall of a mass, the stretching of a spring, the lifting of a solid body, the 

rotation of a solid about a fixed axis, etc. 

Work, together with all the other concepts used to interpret physical phenomena, is expressed 

by a simple mathematical formulation: if the application point of the constant force F moves 

from A to B, the work W is expressed by the scalar product W = F X AB; and the elementary 

work for a displacement 6s, by W = F X 6s. This, of course, pre-supposes a knowledge of basic 

mathematics, but the main point is that each formula should have a physical significance without 

which the pupil cannot grasp the physical reality that the teacher is seeking to convey which is 

what really matters. I personally have seen on pupils’ exercise sheets simplifications introduced 

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into the presentation of the results obtained in calculating kinetic energy, for instance, which 

consisted of the dropping of the coefficient ?4 from the expression %mv2 and which caused the 

final result to lose its true physical significance. 

This method is also used for the introduction of the concept of kinetic energy, which is 

characteristic of systems in movement and hence capable of doing mechanical work. The mathematical 

aspect of the formulation is based on the experimental study of the variations in the 

kinetic energy of the moving body under consideration whose mass is m and whose velocity is v. 

This conforms to a current trend in physics teaching which deserves to be stressed and encouraged, 

for the use of mathematical language makes it easier to choose models whereby physical reality 

can be interpreted. The concept of energy is no exception to this rule. 

A similar approach is adopted for dealing with the concept of potential energy, i.e. the energy 

that a body possesses by virtue of its position. A body that falls from a height h can do work; a 

compressed and immobile spring can do work when it is released. In order to link the mathematical 

formulation with the physical reality, emphasis should be laid on the fact that the arbitrary 

choice of the origin of potential energy (in the case of a falling body, it is natural to consider that 

the potential energy is nil at ground level) leads to far more interest being taken in the potential 

energy variation than in the potential energy itself. 

To return to the purely physical aspect, it is generally agreed that no concept should be 

introduced unless it is accompanied by applications drawing on everyday examples derived as far 

as possible from the pupil’s environment. 

The concept of the mechanical energy (the sum of the kinetic energy and the potential energy) 

of a particular system is then introduced with reference to simple physical systems defined having 

regard to their positions in space. Examples: the system ‘spring, mass rn’ where the weight mg is 

an external force; and the system ‘spring, mass m, rod, Earth’ where the spring and the mass are 

guided without friction along a horizontal rod in such a way as to stretch the spring and where 

all the forces that come into play are internal forces. 

The conservation of total mechanical energy is studied with reference to a mechanically 

isolated system, i.e. a system that is not subject to any external forces or that is subject to 

external forces that balance each other out. By way of example, it may be noted here that the 

system formed by the mass alone is not mechanically isolated, while the system ‘spring, mass 

m, rod, Earth’ is. 

This property of total mechanical energy is linked to the work of the conservative forces 

within the isolated system. These forces are said to be conservative because their work, from the 

initial position to the final position along the path followed when their point of application is 

displaced, depends only on those two positions and not on the path followed. In the opposite 

case, such forces are said to be non-conservative. As an example, one can refer to the frictional 

forces acting upon a moving body as it slides over a plane and whose work depends on the form 

of the path. At this stage in the method employed to define the concept of energy, the pupil’s 

attention should be drawn to the difficulty of generalizing and extending the calculation of 

mechanical energy to a system composed of a very large number of particles (since any material 

system can be regarded as a set of particles). It is always possible to define the mechanical energy 

of a system on a microscopic (molecular) scale, but it would be very difficult, if not impossible, 

to calculate it on the same scale when a large number of particles are involved. 

This naturally brings us to the concept of heat energy, introduced on the basis of examples of 

the non-conservation of mechanical energy in the case of a mechanically isolated system, where 

this non-conservation is linked to the work done by non-conservative forces. The production of 

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heat is interpreted as the result of the degradation of mechanical energy. The particles of the 

system move in a disordered way; and the degraded part of the mechanical energy only serves 

to increase the disorder or agitation of the particles. Work and heat are thus seen to be physical 

quantities of the same kind. 

This idea is supplemented by the demonstration that, conversely, heat can be transformed into 

work. 

At the stage when the pupil is being introduced to these concepts, it is essential to begin to 

familiarize him with the concept of temperature which is closely linked with that of heat. 

Temperature should be seen as a characteristic of particle agitation and hence to be a parameter 

whereby the state of a system can be described. It should be made clear that heat and temperature 

are two separate concepts, and that heat should be considered as a form of energy while 

temperature is a state variable (or co-ordinate). In order to complete the study of the concept 

of heat energy, the effects of heat (combustion, chemical reactions, etc.) should be indicated and 

examples of heat sources should be cited, taking into account the question of heat transfer and 

the concept of thermal equilibrium. 

All this should lead to that part of the course relating to thermodynamics, i.e. the part relating 

to the study of transformations and equilibrium states of systems defined by position parameters 

and temperatures. 

Thermodynamic (or absolute) temperature is defined later at a more advanced level. The 

temperature is a measure of the degree of particle agitation and is defined as a quantity T proportional 

to the kinetic energy of a particle of mass m, moving with velocity of translation 

v : %mv2 = ?2kT, k being a constant and the coefficient % being chosen for reasons of convenience 

which will be justified by the calculations to be made on the basis of thermodynamic models. 

In this part of the course, dealing with thermodynamics, the concept of internal energy is 

tackled. The internal energy of a system is the sum of the kinetic energies and potential energies 

of ail the particles making up the system and attention has already been drawn to the difficulties 

involved in calculating the mechanical energy of systems containing a very large number of 

particles acting upon one another. 

At this stage, which might be said to be an initiation to the concept of energy, the teaching is 

confined to the case of systems which are at rest from the macroscopic point of view, and in 

thermodynamic equilibrium. The macroscopic variables (temperature, pressure, etc.) conserve 

the same values in time and the system conserves its own energy; at equilibrium the energy of the 

system is a constant and is thus said to be a function of state. 

It wil be necessary to help the pupil to grasp the theoretical, not to say utopian, character of 

this definition in the light of the difficulties relating to the microscopic scale. The example can, 

however, be cited of perfect gases for which a model may be adopted in which each atom is 

represented by a dot and there is no need to consider any remote interaction between the atoms. 

Hence, there is no potential energy. In the general case, the variations in internal energy can be 

determined with the help of state variables, which are macroscopic. Here Joule’s experiments 

provide experimental support and make it possible, among other things, to explain the equivalence 

of heat and work. 

Exchanges of energy between the system considered and its surroundings may take place in the 

form of heat or work (with sign conventions according to whether the system receives or gives up 

energy to its surroundings). 

By means of Joule’s experiment it can be shown that a system may undergo an infinite number 

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of transformations, all of which take it from the same initial state to the same final state (thermodynamic 

equilibrium states). Variations in the internal energy of the system do not depend on 

the path followed in the transformation considered. 

The first law of thermodynamics provides a general application of this conclusion to any 

system exchanging only heat and work with the surroundings. As the internal energy is a function 

of state, for any given equilibrium state there wil be clearly defined macroscopic variables; with 

this can be associated a system describing a succession of states of equilibrium, and we thus have 

a reversible transformation. Here it should be pointed out that such a transformation does not 

exist in nature and must be regarded as the limit of a real transformation which is infinitely slow 

and subject to a negligible dissipation of energy. 

CONCLUSION 

In conclusion, and perhaps popularizing somewhat, I shall attempt to introduce the concept of 

entropy. Entropy is interpreted as a measure of the disorder of a system (more commonly 

referred to as the degradation of the system’s energy). It seems reasonable to say that a reduction 

of this disorder is accompanied by a decrease in the entropy and that the entropy is zero at 

absolute zero temperature (all thermal agitation having then disappeared). 

Some attempts are currently being made to popularize the concept of entropy, and it is 

applied in this connection to the universe itself, the latter being regarded as an isolated system. 

It may then be considered that the universe, which is the site of irreversible real transformations, 

does not pass through the same state twice. 

We may therefore visualize entropy as continually increasing and attaining its maximum value, 

thus leading to a universe in which the temperature would be the same at every point, which 

would preclude any form of life (an eventuality known to be very remote). 

The second law of thermodynamics provides us with a better understanding of this aspect in 

everyday life. In the same way as, in order to put a hydraulic machine into operation there must 

be a difference in levels, a thermal machine can operate only if there is a temperature difference, 

that is, two sources of heat at different temperatures. 

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The planning and developing of an instructional system 

based on the classroom use of textbooks, with reference to 

energy, entropy and irreversibility 

C.Z. DIB. H.U. GAMA AND S. MAGRINI. 

Brazil 

The objective of this project was the planning and development of a physics learning system using 

the principles of educational technology. Its starting point was the classroom use of a textbook. 

The research team decided to base the system on the classroom situation as it exists, taking 

due note of (a) the motivation and the degree of proficiency of the teachers, (b) the books, 

experimental equipment and audio-visual resources available and (c) the social, economic and 

cultural levels of the students. 

This realistic approach led the team to start with an existing textbook and then to strive for 

the optimisation of its use in the classroom. At the core of this process, they placed reading and 

discussion, supplemented by group work, practical work, etc. 

It was appreciated that the textbook's qualities of clarity, intelligibility, precision, etc. would 

play a fundamental role in the whole process - even to the extent of determining the success or 

failure of its application. It follows that the approach adopted may also serve to diagnose the 

didactic quality of textbooks. 

AN EDUCATIONAL TECHNOLOGY MODEL FOR THE CLASSROOM USE OF TEXTBOOKS 

Planning the activities 

Before using the proposed technique, the teacher must himself read the textbook in order to 

acquaint himself with it, to analyze the content and the presentation, to gauge the intelligibility 

of both text and the illustrations and to check the suitability of the exercises proposed. A full 

diagnosis and analysis might take two or more readings. 

During this diagnostic period, the teacher wil try to specify his objectives and to match these 

to possible student activities which wil include (a) reading the text, (b) discussion, (c) clarification 

and/or explanation by the teacher as points arise during the discussion and (d) doing exercises 

(whether individually or in groups). 

Specifying the objectives themselves wil depend on the teacher's approach to the subject 

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matter, on his professional experience and on his proficiency in the subject. In the first instance, 

this is best done in terms of task specification; the operational statement (i.e. the questions and 

answers which can be accepted as evidence that the proposed objectives have been achieved) 

follows later. This specification of basic objectives is essential since it is these objectives which 

serve as guides to all the activities undertaken in the classroom. 

The ease with which teachers describe these basic objectives is a function of the quality and 

clarity of the text itself. Difficulties may arise if the text is incomplete, ambiguous and therefore 

confusing, or illogically sequenced. This provides a very good test of the quality of the text. 

One of inferior quality wil give rise to unsatisfactory learning and wil demand extra effort from 

the teachers to explain the difficulties it creates. 

It wil be necessary, whilst reading the text, for the teacher to assess the likely familiarity of 

any prerequisites (in physics or mathematics) to the students. Once this has been done, the 

teacher wil be able to plan the necessary revision, either by direct teaching and discussion, or 

by the use of printed materials for reading and debate. He must make such revision dynamic and 

interesting since its success is essential. 

Since the objectives are to be attained by reading and group discussion as well as by the 

solution of problems (or exercises), the teacher must facilitate the process by determining 

precisely what is to be read, estimating the time required, specifying the problems to be solved 

(either individually or in groups) and preparing himself to explain whatever may be necessary 

when those problems are attempted. 

Immediately after the reading by the students, the teacher should initiate a discussion on the 

main topics covered. His own contribution to this must be carefully planned and he must be 

prepared to clear any doubts and to answer any questions which may arise. Ideally, he should 

guide the discussion so that the group can itself answer its own queries and resolve its members’ 

difficulties. 

The teacher’s plan wil include a list of the items to be reviewed (succinctly), of questions to 

be asked and such other matters as may be of interest. 

Difficulties experienced by the students during their reading have to be diagnosed so that they 

may be dealt with during the discussion. If necessary, the teacher may need to explain some 

points of obscurity in greater detail than the text provides. 

It may be necessary to establish some supplementary objectives which have particular reference 

to the theme in question. These might allow the teacher to elaborate on the subject matter of the 

reading and to analyze, in depth, other aspects of the theme. In doing this, the teacher brings his 

own personal touch to the material of the text. 

The teacher must steer a path between, on the one hand, establishing too many supplementary 

objectives (which would imply that the text was inadequate for his purposes) and, on the other 

hand, accepting that the established basic objectives are entirely sufficient. 

Establishing such supplementary objectives makes it necessary to determine the activities 

proposed - explanation, readings of other texts, performing experiments, viewing films etc. - 

and the discussion which wil follow. 

It is vital to maintain the students’ motivation at a high level both before and throughout 

their reading. Teachers need to provide for this by, for instance, reporting historical events relating 

to the subject matter or to the lives of the scientists involved, offering relevant anecdotes, 

proposing problems for solution, demonstrating suitable experiments, presenting films,slides 

and other audio-visual material. 

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Criteria for the assessment of the students’ learning depend on the specification, in operational 

terms, of the basic and the supplementary objectives. This process, too, requires careful planning, 

and the teacher must ascertain whether, on average, the students have attained the objectives 

proposed. 

Should the assessment be based on written tests, individual corrections must be made as soon 

as the students hand in their papers. Doubtful points may be explained after this has been done. 

Should the assessment be oral, the teacher must attempt to include all the students. This is a 

simple way to assess achievement of objectives lesson by lesson and assessment can take place 

simultaneously with the discussion. 

Once the planning is complete, the teacher will have available: (a) a list of basic and supplementary 

objectives, (b) a list of pre-requisites with plans for their treatment, (c) plans for discussions 

on the reading which has been done, (d) plans for relevant activities, (e) plans for ensuring 

motivation and (f) plans for assessment. Item (a) apart, these do not require too much effort 

from the teacher. But they wil enable teachers to conduct their classes in an organized and 

controlled manner. 

Carrying out the activities 

Once the planning stage has been completed, the classroom activities follow in sequence. The 

order may be adjusted to suit the subject matter, or the needs of the students, or the availability 

of time, but it may be summarized thus: (1) revision of the pre-requisite material, (2) motivational 

activities, (3) reading the text, (4) discussion, (5) activities related to the objectives (both basic 

and supplementary), (6) assessment, correction and discussion, and (7) final assessment. 

Revision. Revision of the pre-requisites by the teacher can be offered as a lecture (in which the 

teacher must ensure the participation of all the students by his use of such questions as ‘What is 

the first law of thermodynamics?’ or ‘Which process is used to solve this equation?’) or as the 

reading of a text followed by a teacher-led discussion. 

Motivation. Whatever the method used to provide motivation (lecture, anecdote, practical 

work, demonstration, etc.), it is essential that all should be fully involved. If convenient, the 

scheme for motivation may precede that for revision. 

Text reading. Once sure of the motivation of the students, the teacher should encourage the 

group to proceed with the reading activities he has planned. He should write the appropriate 

page numbers, the time available and the list of the basic objectives on the blackboard so that 

everyone knows precisely what is required. When such work is undertaken for the first time, a 

group wil require guidance. They should be told that although the reading has to be done 

individually interaction among the participants (covering explanations, the exchange of opinions, 

etc.) is allowed, that they should make notes of any doubts they may have so that these may be 

considered in subsequent discussion and that they may consult the teacher. 

Discussion of the reading. Using the plan he has prepared, the teacher wil lead a discussion on 

the material read; such a discussion should relate to all the material covered and should include 

questions addressed to individual students. The teacher may find it necessary to stimulate discussion, 

to ask questions and to raise difficulties himself. This wil be especially true in the early 

stages for then students are unwilling to participate fully. But, as they recognize the essential 

part played by discussion in the learning process, this wil change. 

Activities related to the basic and supplementary objectives. These include the reading itself, 

the discussions and explanations as well as the problem-solving exercises. The teacher, having 

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ensured that the reading and the discussions are complete, has next to co-ordinate the doing of 

the exercises and to provide the other activities he has planned. And, in the final minutes of a 

lesson, he may wish to return to the motivation theme. 

Assessment, correction and discussion. Once the planned programme is complete, the teacher 

must assess whether or not his objectives have been achieved. This requires the students to 

perform the assessment tasks, the correction of any papers submitted and the clarification of any 

remaining difficulties. 

Final overall assessment. The teacher may wish to effect a final assessment when his class has 

completed a theme or a chapter. This might give opportunity for further discussion. 

The entire scheme outlined above is not intended to be rigid. It wil require reformulation 

to adapt to the learning conditions which obtain. But the central part played by the reading must 

remain since all the other activities have been developed around it. 

A SAMPLE SECTION FROM THE TEXT 

To illustrate how the model operates, a text was written at a level suitable for secondary schools 

on the topic of ‘Energy, Entropy and Irreversibility’. It was the intention to offer, in form and 

content, a traditional text, rather than to prepare a didactically sound one, for a basic objective 

of the project was to present a model applicable to any existing textbook, independent of its 

didactic quality. The contents are listed in Table 1. 

The sample wil be restricted to items 1, 2 and 3. 

TABLE 1. Contents of the whole text. 

1. 

2. 

3. Reversible and irreversible processes. 

4. Heat engines; Carnot’s cycle. 

5. 

physical systems; the boundaries and the surroundings of a system; open and isolated systems. 

Natural processes and the orientation of spontaneous physical processes. 

Entropy: the second law of thermodynamics. 

6. Conclusions. 

7. Exercises. 

1. Physical systems; the boundaries and the surroundings of a system; open and isolated systems. 

(a) Physical systems. In studying any natural phenomenon we concentrate on a restricted 

area within the universe. Consider the following instances: (i) the detonation of an explosive 

somewhere on Earth; (ii) the melting of an ice cube in a container of warm water; (iii) the path of 

a charged particle in the electric field between two parallel plates; (iv) the behaviour of a gas 

contained in a cylinder fitted with a moving piston. 

Each of these examples restricts our attention to a limited part of the universe. Any part of 

the universe isolated for such study may be called a system. A system is any part of the universe 

which is isolated either physically or mentally for the study of its properties. 

Thus a chemical or a nuclear explosive can be considered as a system. A container filled with 

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water and ice is a system which may be studied for its thermal properties. The parallel plate 

capacitor and the charged particle form an adequate system for the study of the behaviour of 

charges in nearly uniform electric fields. 

(b) System boundaries. Let us consider a system comprising a gas contained in a cylinder 

which is fitted with a moving piston (figure 1). The surface that circumscribes the system is 

named the boundary of the system, 

piston 

boundary 

gas 

boundary 

Figure 1. The boundary of a system is determined by the surface that circumscribes it. 

Boundaries may or may not be fixed. When the gas within the cylinder acts on the piston and 

moves it, we have a moving boundary. On the other hand, a thermos bottle is a system with a 

fixed boundary. 

(c) The surroundings of a system. In the example of figure 1, the gas, the cylinder and the 

piston constitute a system with boundaries as shown. The remainder of the universe constitutes 

the system’s surroundings (figure 2). 

Figure 2. The surroundings of a system make up the environment in which it is located. 

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A system’s surroundings may also be called the environment in which it is located. A system’s 

environment exerts direct or indirect influence over the system. In this case, the atmosphere that 

is part of the system’s environment exerts pressure on the piston. 

(d) Open and isolated systems. Systems may be either open or isolated. For example, man is 

an open system since he interacts with his surroundings. He inhales, exhales, eats and so on. A 

truck loaded with sand that is shedding part of its load is an open system, since it transfers matter 

- mass - to its surroundings. A good, firmly closed thermos bottle can be considered as an 

isolated system for a certain, short interval of time since, during that interval, it exchanges almost 

no energy (heat) or matter with its surrounding environment. 

Figure 3. A truck loaded with sand that sheds part of its load is an open system. 

An open system is any system that interacts with its surroundings, exchanging matter and/or 

energy with its environment (figure 3). An isolated system is any system that does not interact 

with its surroundings; no energy and/or matter interchange with the environment occurs. 

2. Natural processes and the orientation of spontaneous physical processes. 

(a) Nature conserves energy. No exception to the Principle of Conservation of Energy has 

ever been observed in nature. For example, in isolated mechanical systems, the total mechanical 

energy remains constant. Consider a freely falling body within a closed vacuum tube. In this case 

the tube and the falling body constitute an isolated system. While the body is falling, its gravitational 

potential energy becomes kinetic energy. However, the total mechanical energy is conserved. 

Should the tube be filled with air, the system becomes an open one. In this case some of the 

mechanical energy would be transformed into heat by friction with the air molecules. 

The Principle of Conservation of Energy is one of the most important in Physics. It states that 

no energy creation or destruction ever occurs in any of nature’s processes. There are only energy 

transformations. We can transform potential energy into kinetic, mechanical energy into thermal 

or electric energy, atomic or nuclear energy into heat and so on. But the total energy of the 

universe wil always stay the same. 

(b) A preferential direction for natural processes. Heat flows spontaneously from a body at 

a high temperature to another at a lower one. Should the reverse take place, that is, should heat 

be transferred spontaneously from the cooler to the warmer body, the total amount of energy 

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(heat) would still be conserved. But this does not occur. There is, in nature, a preferred direction 

for the occurrence of such spontaneous processes. Lakes, for example, don’t freeze spontaneously 

on a warm day by surrendering heat to their surroundings even though such a process would 

conform to the Principle of Conservation of Energy. 

To take another example, consider a body which is falling freely through the air. Potential 

energy is transformed into kinetic. In addition, friction wil cause both the air and the body to 

warm up. Potential energy is transformed into kinetic energy and heat. But the reverse process 

has never been observed; that would involve the thermal energy of the molecules of the air and 

of the body to be added to the kinetic energy of the body, and might even drive the body upwards! 

The Principle of Conservation of Energy would not exclude this (see figure 4). 

There exists, then, a preferred direction for the occurrence of spontaneous natural processes. 

Any inversions of this direction can only occur when an external agent exerts an influence over 

the system considered. 

We say that processes are irreversible when no reverse transformation can be made spontaneously 

by the system. As we shall see later, spontaneous processes lead systems into less organized 

states of energy. 

Figure 4. Transfer of thermal energy from the atmosphere to a falling body, driving the body upward, has never been observed. 

3. Reversible and irreversible processes 

Consider a system made up of a gas-filled cylinder fitted with a moving piston. Suppose that 

the gas wil be led from the initial state i to a final state f, through intermediate and well defined 

pressure, volume and temperature states. If any small change in the environmental conditions 

(of temperature, volume or pressure) can take the system back from state f to state i, through 

the same intermediate states, the process is a reversible one. 

However, if the pressure, volume and temperature of the gas cannot be perfectly defined for 

each of the intermediate states, or if a small alteration of the environmental conditions cannot 

take the system back from state f to state i through the same intermediate states, the process is 

irreversible. 

Nature does not provide for rigidly reversible processes. But when a transformation from 

state i to state f is sufficiently slow, an almost reversible process takes place. 

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For example, should we throw one kilogram of sand all at once on to the piston of the cylinder 

(figure 5) the gas compression process would be irreversible. But, should we throw the same mass 

of sand on to the piston gram by gram and very slowly, the gas would undergo a reversible 

transformation between the states (figure 6). If the sand were slowly withdrawn, the gas would 

return from state f to state i through the same intermediate states. 

sand 

Figure 5. If 1 kg of sand is thrown all at once on to the piston, the gas compression is irreversible. 

Figure 6. If 1 kg of sand is placed on the piston, grain by grain, the compression is reversible, provided that the sand is withdrawn 

equally slowly. 

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Consider a further instance. If the gas temperature is suddenly increased by putting the cylinder 

in contact with a reservoir of heat at a higher temperature, the transformation which occurs wil 

be irreversible. But we may achieve the transformation through a nearly reversible process 

between the same states of temperature, pressure and volume. We must put the cylinder into 

contact with a series of several reservoirs at slightly different temperatures. Thus, if we wish to 

increase the gas temperature from Ti to Tf, where Tf>Ti, in a reversible way, we must provide 

several reservoirs with temperatures Ti + A T; Ti + 2 A T; Ti + 3 A T . . . etc., where AT corresponds 

to a small temperature increase. 

At each stage we must allow sufficient time for the gas and the cylinder and the heat reservoir 

to reach thermal equilibrium; this process must continue until the gas reaches the desired 

temperature Tf. 

APPLYING THE MODEL TO THE SAMPLE OF THE TEXT 

One lesson was thought necessary to cover the material quoted in the above sample and the 

planning of that lesson is detailed below. 

1. Reading 

2. Identification of basic objectives 

(a) Task specification 

To define a physical system. Give examples. 

To define the boundary and the surroundings of a system. Examples. 

To distinguish between open and isolated systems. Examples. 

To give examples of processes which, although not occurring spontaneously in nature, do not 

infringe the principle of conservation of energy. 

To define reversible and irreversible processes. 

(b) Specification of operational objectives 

Q. Define a physical system. Give examples. 

A. A physical system is any part of the universe which is either physically or mentally 

isolated for study. Examples: the Milky Way; the Earth/Sun system; a charged object in 

an electric field; a particle in motion; any similar response. 

Q. Define ‘boundary’ and ‘surroundings’ of a system. 

A. The boundary of a system is the surface that encircles it. Excluding the system itself, the 

remainder of the physical universe constitutes a system’s surroundings. 

Examples: Consider (a) a soft drink bottle as a system. The rest of the universe constitutes 

the surroundings. The outer surface of the bottle is the boundary of the system. 

(b) gas contained in a cylinder and enclosed with a piston. The rest of the universe is the 

surroundings; the outer surface of the cylinder and piston is the (movable) boundary. 

(c) any equivalent example. 

Q. Define an open and an isolated system. Give examples. 

A. A system is open when matter and/or energy can be exchanged with its environment. 

Examples: a soft drinks bottle after being opened; animals; plants; a pan during cooking. 

A system is isolated when matter and/or energy cannot be exchanged with its environ- 

141


ment. Examples: a tightly closed thermos bottle; a body in free fall in an evacuated 

container; any equivalent answer. 

Q. Give some examples of processes that would not infringe the principle of conservation of 

energy but which do not occur spontaneously. 

A. A flow of heat from a body at a low temperature to one at a higher temperature. 

The transformation of kinetic into gravitational potential energy. 

Q. Define reversible and irreversible processes. Give examples. 

A. A process is reversible if the system is able to revert from final state f to initial state i 

through the same intermediate states as in the transformation from i tof. When no such 

reversion is possible the system is irreversible. All spontaneous natural processes are 

irreversible: some non-spontaneous, extremely slow transformations are nearly reversible 

(or any equivalent answer). 

3. Planning the revision of the pre-requisites 

During this first lesson, the existence of the necessary pre-requisites must be assumed. 

4. Planning activities related to the basic objectives 

Such activities will include revision and discussion of points within the reading matter which the 

teacher deems relevant. 

5. Planning the discussion of the reading 

This discussion wil consider examples of physical systems, the boundaries and the environment 

of a system, the difference between open and isolated systems (with examples), the conservation 

of energy, the existence of a preferred direction for the occurrence of natural phenomena, 

spontaneous processes, reversible and irreversible processes. 

6. Determining supplementary objectives 

(a) Task specification 

To demonstrate that no rigidly isolated systems exist in nature. 

To demonstrate that spontaneous processes occur in such a way as to direct the system 

towards the most probable energy states. 

(b) Specification of operational objectives 

To demonstrate that no rigidly isolated systems exist in nature. 

Examples: commonly used examples of isolated systems include thermos bottles, calorimeters 

and Newton’s vacuum tube. A thermos bottle is a system that, over a certain period of time, 

conserves the temperature of a liquid at the level it was at when poured into the bottle; 

however, some measure of exchange with the surroundings occurs even over short time 

intervals. A calorimeter is a container which insulates a substance thermally from the environment 

in which it is located. However, since no perfect thermal insulators exist, some measure 

of heat interchange with the environment wil occur. Newton’s vacuum tube is a system used 

to study the fall of bodies in a vacuum. However, as a perfect vacuum cannot be produced, 

a certain amount of the mechanical energy of the falling body wil be dissipated by friction 

with the air molecules in the tube. 

142

Brazil 

An isolated system is an abstraction used to simplify matters when solving some problems. 

Rigidly isolated systems do not exist in nature. Or any similar answer. 

Q. Demonstrate that spontaneous processes occur so as to direct the system towards the 

most probable states of energy. 

A. The ‘entropy’ of a system is related to the probability that the system wil be in a certain 

state of energy. 

The most probable energy states, i.e. those with a high probability of occurrence, are 

those with the highest entropy. This can be verified through the defining equation for 

entropy S = klnW, where S is the entropy of a system in a certain state of energy, k is the 

Boltzmann constant and W is the probability of occurrence of the state concerned. This 

equation links classical and statistical thermodynamics. According to the second law of 

thermodynamics, spontaneous processes take place in such a way as to increase the entropy 

of the universe, leading the system to the most probable state of energy. The increase 

of entropy of the universe can be interpreted statistically in terms of the probability of 

occurrence of energy states in a system. 

7. Planning activities related to the supplementary objectives 

The teacher shall perform such activities only in the event that there is sufficient time and if the 

proficiency level of the students is adequate. They might include: 

A lecture showing that the systems offered as examples of isolated systems are not perfect 

since they interact with the environment even over the smallest time interval. 

An explanation of some of the concepts of statistical mechanics at any appropriately elementary 

level. 

8. Planning for motivation 

Motivation is assisted by presenting students with interesting phenomena or events in physics, 

without providing an explanation. So the teacher might show how energy is conserved in the 

spontaneous freezing of a lake on a summer day, or when a simple pendulum starts to swing, 

impelled by the moving air molecules. Then he might ask the students why such events don’t 

occur since the Principle of Conservation of Energy is observed. 

9. Planning the mode of assessment 

The teacher wil encourage student participation in discussion. Then, he wil be able to assess 

whether or not the basic objectives were generally attained. And during his treatment of the 

supplementary objectives, he will be able to verify whether or not these objectives were achieved. 

Should it be possible to obtain written answers from the students, or from groups, and to correct 

these, the teacher wil be better able to assess the students’ achievement. 

143


Energy education in the United States 

J.M. FOWLER. 

HISTORY AND NEED 

There were prophets of course. King Hubbert [ 1 ] of the United States Geological Survey (USGS) 

warned us as early as 1949 and continuously through the late fifties and the sixties that oil consumption 

in this country was growing faster than was our capacity Yo produce it. And about that 

same time, Ayres and Scarlott saw the coming energy crisis even more broadly and discussed the 

necessary measures to soften it in their brilliant but apparently little noticed book, Energy 

Sources: The Wealth of the World [2]. But there weren’t enough prophets and certainly not 

enough converts. 

When the members of the Organization of Petroleum Exporting Countries (OPEC) shut off the 

oil flow in the fall of 1973, engines sputtered and fires burned low in this country and in much of 

the rest of the industrialized world. 

The dominant response to the crisis was political and therefore short-term. We were urged to 

‘conserve’ energy (i.e. save it) and the big oil companies demanded to be turned loose from the 

constraints of regulation to produce more (there were profits aplenty even if prophets were 

lacking). But by early 1974 some of those making policy recognized that education had a role. 

That role recognition and a sense of urgency also sprang up at the grassroots level and ‘energy 

education’ began. 

The early efforts in education were almost entirely ‘conservation’ or saving directed: ‘slow 

down, turn it down or turn it off. Most of the effort in energy education is still directed towards 

saving. The shocks of the oil embargo of 1973-1974, the shortage of natural gas in the winters 

of 1976 and 1977 and the return of queues of automobiles to the filling stations in the spring 

of 1979, however, drove home the fact that this country and the world had entered a period of 

major transition in energy use. Educators faced the challenge of preparing a generation for that 

transition. Tomorrow’s citizens, today’s students, needed to know that the era of abundant and 

inexpensive energy was over and the only certainty of energy’s future was that it would be costly. 

They needed to learn to recognize energy realities and disregard the myths (‘it’s all a conspiracy, 

there’s plenty of oil. . .’). They needed to study the risks and benefits of the possible paths to the 

future. At both the college and pre-college level, course and curriculum development with 

broader shape began. 

144

United States 

LEVELS AND TACTICS 

Energy courses at the college level had begun in a few places even before the embargo. My own 

course, Energy and the Environment which led to the book of the same name [3] was first 

taught at the University of Maryland in 1972. The Wilson-Jones book, Energy, Ecology and the 

Environment [4] out of MIT/Harvard and Romer’s book, Energy: A n Introduction to Physics 151 

also suggest earlier course development. 

College courses are generally of two different types. There are the energy courses built around 

books [3, 6-10] which are designed to deal with the broad theme. There are also books whose 

structure is disciplinary - physics or chemistry and more lately economics [ 5, 1 1 - 171 - but 

which illustrate the applications of the discipline with energy examples. 

College level courses and the few examples of energy programmes [ 181 are the products of 

academic entrepreneurs. Their courses or programmes were submitted to and approved by faculty 

committees and then tested in the student market. 

Energy education in the schools 

It is much more difficult to introduce new courses at the school level. The curriculum has always 

been full and the social crusades of the sixties overfilled it, adding sex education, drug education, 

consumer education, etc. There is no room for an ‘energy education’ curriculum and the ‘back to 

basics’ backlash of the late seventies makes the introduction of new material even more difficult. 

There are successful course development examples in spite of the difficulties. Most of these 

are at the high school level where there is still some room for electives [ 19, 201 . Some of the 

energy education projects under development are producing add-on materials which are intended 

to be taught as coherent units [ 21-23] . Other projects, however, have tried to produce materials 

which fit into various pedagogical nooks and crannies of the existing curriculum. This is the 

‘infusion’ approach. The National Science Teachers’ Association (NSTA) Project for an Energy- 

Enriched Curriculum (PEEC) is an example for later description. 

Public vs. private sector 

Another approach to energy education drew upon a different source of funds. The NSTA’s 

entrance into energy education was supported by a contract from the Office of Environmental 

Education of the United States Office of Education.’ One of the products of this first contract, 

the NSTA Energy-Environment Source Book [24], has reached a distribution of about 35,000 

and is still unique in the field. This contract was followed by support from the Federal Energy 

Administration (FEA), then the Energy Research and Development Administration (ERDA) 

and finally the Department of Energy (DOE). While the variety of supporting agencies is impressive, 

the amount of funds is not. None of these agencies had more than few million dollars per 

year for energy education curriculum development. The DOE money, for instance, supported 

the five-year effort in curriculum development of PEEC, the ‘Science Activities in Energy’ 

development of the Oak Ridge Associated Universities, a series of sixty to eighty Faculty Development 

summer institute programmes, and isolated efforts such as the home economics materials 

developed at the University of Tennessee. 

The private sector also began to produce materials and to support energy education in the midseventies. 

The electricity supply companies or electric utilities, which have strong local ties, 

already had some experience in co-operative programmes with schools and when ‘Reddy Watt’ 

(who promoted expanded electrical use) changed to ‘Save-A-Watt,’ some companies began to 

produce and distribute energy conservation-oriented materials in the schools. 

145


These local and conservation-oriented programmes led to more ambitious efforts. In the early 

seventies the Edison Electric Institute developed and tested the Energy Environment Game - a 

board game based on the problem of selecting and siting an electric power plant. This was 

distributed to schools through local electricity supply companies. 

On the West Coast a co-operative effort between some of the electric companies and educators 

began the development of the Energy and Man’s Environment (EME) project which now runs its 

teacher awareness workshops and training sessions in fifteen states. EME has been joined more 

recently by ‘Captain Power’, a course for second and third graders produced for the San Diego 

(California) Gas and Electric Company, the ‘Energy Information Resource Kit’ series for high 

school students sponsored by the Edison Electric Institute and two energy books - one on 

energy conservation and the other on energy sources - funded by Exxon. 

An overall view of the variety of material which fits the description ‘energy education’ can be 

obtained from a survey of the informal PEEC curriculum library. This library, built of materials 

sent by developers all over the country, now contains some 400 items, ranging from brief background 

pieces on the energy crisis and suggested lists of activities on energy to curriculum projects 

extending over the whole range of schools from kindergarten to grade 12. While this library is 

not a complete collection, it is probably representative of the major efforts. 

Of the 4 12 separate pieces cataloged, 133 could be called curriculum units. Some 20 of these 

are directed at all grades, 32 are for elementary classes, another 32 for middle or junior high class, 

41 are targeted for the high school and 8 are for Two-Year or Junior Colleges. 

The developers are equally varied. Of the 309 pieces that are instructional units (rather than 

directories, policy statements, articles, etc.), 27 were developed by State Energy Offices, 52 by 

State Education Agencies, 53 were produced by some federal agency, 30 by local school districts, 

and 4 by individual teachers (this figure is probably distorted; the library would not be likely to 

receive much material directly from teachers). There were 77 items produced by corporations or 

by others in the private sector and 66 by non-profit groups or universities. As pointed out, much 

of the effort at the state level and in the non-profit groups was ultimately dependent on federal 

funds. 

We have also looked at those projects with clear energy themes. That breakdown is recorded 

in Table 1. As expected, ‘conservation’ themes dominate the list. The absence of materials 

on nuclear energy is striking (although a few are included under the category ‘fuels’). 

TABLE 1. Number of Projects Having Clear Energy Themes 

Theme 

Conservation 

Energy Basics/Awareness 

Solar 

Environment/Ecology 

Energy Management 

Buildings/Transport 

Fuels 

(including nuclear, biomass) 

Careers 

Total 

146 

Total 

64 

53 

36 

25 

32 

53 

13 

276

United States 

The private sector spends about $30 million per year (a conservative estimate) on energy education. 

Much of the earlier material was biased and could be rightfully criticized for ignoring the 

environmental impacts of energy production and consumption, stressing production rather than 

‘conservation’ or blaming ‘governmental regulation’ for the energy problems. This outlook has 

changed, however. The private sector is now in better communication with educators and is 

producing more balanced material. Much of the credit for better communication must go to the 

educational representatives of the various energy industry associations. An informal group, the 

Energy Educators Forum [ 271 , representing five of these associations has served for some years 

on PEEC’s Steering Committee and has contributed in many ways to the development of a 

national identity for energy education. 

THE CONTENT OF ENERGY EDUCATION 

Energy education materials developed before mid-1 978 were listed at the request of the Education 

Division of the former Office of Education, Business and Labor Affairs, United States DOE. 

The two volumes produced by this contract contain about 5000 entries. Any thorough study of 

energy education materials would be crushed under this weight. It can be safely predicted, however, 

that the vast majority of the listed materials emphasize individual ‘conservation’ or are background 

pieces for teachers that describe the decline of fossil fuel resources. 

It appears, in fact, that energy education in the United States began with an awareness stage - 

‘Why are there queues at the filling stations?’; quickly entered a mission-oriented stage - ‘conservation’ 

- and is now approaching curriculum integration. It is this integration of the complex 

concepts of what I call energy/environment/economics (E/E/E) into the curriculum at all levels 

and in all courses that I define as energy education. 

The hidden curriculum of PEEC 

NSTA’s PEEC, which is supported by the United States Department of Energy, has developed 

over the years a list of ‘Major Concepts in Energy/Environment/Economics’. This list, in an 

abbreviated form is shown in Table 2. It is our hidden curriculum. 

TABLE 2. Major concepts for Energy/Environment/Economic Education 

~ 

A. Energy basics 

(1) Forms and states of energy 

(2) Forms and states of energy available on earth 

(3) Energy conversion processes 

(a) Energy units 

(4) Energy flows through natural and industrial systems 

(a) Power and power units 

B. Natural laws of energy and energy use 

The first law of thermodynamics 

(a) ‘Losses’ and efficiency 

The second law of thermodynamics 

(a) Energy usefulness 

Energy resources 

Patterns of consumption 

Patterns of growth and their implication 

147


C. Environmental effects of energy production, transport and consumption 

(1) Effects of extraction 

(2) Effects of transport and distribution 

(3) Effects of consumption and discharge 

D. Societal effects of energy production and consumption 

(1) Economic effects 

(a) Capital use, prices, employment 

(2) Lifestyle and other domestic effects 

(3) International Policy and National Security 

E. Energy policy 

(1) State, Local, Federal, etc. roles 

(2) Costbenefit consideration 

(3) Production stimulating strategies 

(4) Conservation stimulating strategies 

F. Energy futures 

(1) Mid-term (1980-2000) options 

(2) Long term (2000) options 

(3) Social, economic, and environmental effects of future options 

~ 

It is intended to be taught in a spiral fashion. Children need an early introduction to the abstract 

notion of energy. ‘E the Magnificent’ in the PEEC kindergarten packet, is a puppet who can 

change form from light to heat to motion. ‘E’ represents potential energy when he or she is resting 

and kinetic energy when active. 

The energy basics are returned to at higher grade levels with more sophistication. The technologies 

for converting energy from one form to another are introduced and energy is presented 

as something that flows through systems. It drives biological cycles and in analogous ways drives 

our industrial society. The basics continue into the high school level where the two natural laws 

of energy, the First and Second Laws of Thermodynamics, are presented in the PEEC classroom 

packet, The Natural Laws of Energy. 

At the upper elementary or middle school level (students 10 to 14 years old), the viewpoint 

is broadened beyond energy to include the effects of energy production, transportation and 

consumption on the environment. Strip mining, oil spills, air pollution and acid rain are seen as 

part of the E/E/E picture. And economics enter here. Energy is a commodity that is bought and 

sold. It is something that can be invested in (the PEEC packet Energy as an Investment Choice). 

The economic laws of supply and demand can be readily illustrated with oil for example (Energy 

in the Global Marketplace). 

Filling out the E/E/E picture then requires an understanding of laws, policies and political 

strategies. The American legislative process can be taught with a PEEC packet called How a Bill 

Becomes a Law to Conserve Energy which follows the 55 mile per hour national speed limit law 

through Congress. The making of policy by the Executive Branch is shown in the PEEC packet, 

US. Energy Policy; Which Direction? which presents the historical picture of how the 1977 

National Energy Plan was established by the Carter Administration. 

There are also packets for mathematics teachers (Mathematics in Energy, The Exponential 

Energy Century, The Arithmetic of Energy Conservation) and for English classes (Critical 

Thinking in Energy), 

148

United States 

The progression shown in the list of major concepts appears to be from science to social 

studies and there is such a progression. The real problems of energy are the social ones - economics, 

employment, domestic and international policies, environmental impacts, consumer v. producer 

concerns, etc. The scientific technological problems of increasing conversion efficiency, getting 

new fuels from coal and tapping solar and other renewable sources for energy pale beside them. 

We must not hide this from our students. 

But science must be there to inform and explain the technology and its impact and to help 

clarify the value judgements in the social area. The uninformed rhetoric of many of the antinuclear 

protestors and the exaggerated claims of solar enthusiasts point to a failure of science 

teaching. But we fail so often. 

What makes the E/E/E theme so attractive to the committed energy educators in the United 

States is just this pervasiveness. It crosses discipline boundaries and links what we want our 

students to learn in the classroom to real and important happenings in the world. To properly 

handle this theme, the science teacher can’t ignore economics and social consequences, and the 

social studies teacher can’t ignore science. 

AN ENERGY EDUCATION PROJECT 

An ‘energy education project’ was beginning with the United States Office of Environmental 

Education contract in 1974. A brief description of the various components of that project wil 

illustrate our experience with what is needed to introduce energy into the curriculum. 

Curriculum projects in the United States, in particular those sponsored by federal money, 

must accept (and do so happily) a particular disadvantage. The school system is a ‘bottom-up’ 

system with local districts exercising autonomy. If material developed at the national level is 

to permeate the system, it has to get there on its own merit through the mechanism of promotion, 

publicity and persuasion. There is another handicap, of course, which is probably not unique 

to the system, and that is the crowded state of the curriculum. It is our recognition of the fullness 

of the curriculum that caused us to use the infusion approach; to try to provide energy examples 

for learning goals that teachers already have accepted. 

Another fact of life in education which is strongly influenced by the crowded curriculum is 

that most teachers don’t develop their own materials. They need hands-on, complete packages 

of material that they can pick up and deliver with only a brief review. Thus, we recognized from 

the beginning that although the background materials which we produced (the Energy-Environment 

Sourcebook), and the Fact Sheets would enable a few dedicated and enthusiastic teachers to 

introduce energy themes into the classroom, those materials would not do the job alone. In 

1976, therefore, we proposed to the Energy Research and Development Administration (ERDA) 

that a large scale curriculum development project should be undertaken. 

PEEC has three major components. Classroom packets form the core of our operation. These 

are the interdisciplinary packets described above and intended for infusion. The coverage of our 

‘hidden curriculum’ (see Table 2) is now, in our view, essentially complete. In Table 3 we list by 

title and brief description the packets that have been developed in the five years of PEEC’s 

existence. Those with double asterisks (**) are in print; and those with single asterisks (*) are in 

final form (as far as we are concerned) and await clearance and printing by DOE. The others have 

undergone classroom testing and are in the process of review and revision by the PEEC staff. 

149


TABLE 3. PEEC Packets 

** The Energy We Use 

Grades 1-2, Science 

** Community Workers and the Energy They Use 

Grades 2-3, Social Studies 

**Energy and Transportation 


**Networks: How Energy Links People, Goods and 

Services 

Grades 4-5, Science and Social Studies 

**Bringing Energy to the People: Ghana and the U.S. 


+* Two Energy Gulfs 


**Energy, Engines, and the Industrial Revolution 


** Transportation and the City 


**Mathematics in Energy 

Grades 7-8, Math 

**Energy Transitions in United States Histoly 


**Energy in the Global Marketplace 

Grades 9- 1 1, Social Studies and Economics 

**How a Bill Becomes a Law to Conserve Energy 

Grades 9, 1 1, 12, Social Studies 

**Agriculture, Energy and Society 


** US. Energy Policy: Which Direction? 


* There3 Enough Energy, So What S the Problem? 


Nuclear Energy 


Solar Energy 

Grades 7-9, Science and English 

Bio fuels 

Grades 10-1 1, Science 

* Coal: Promise and Problems 


All packets are available free of charge from: 

U.S. Department of Energy 

Technical Information Center 

P.O. Box 62 

Oak Ridge, Tennessee 37830 

*Energy for the Future 

Grades 1 1- 12, Science 

Energy and Water 


*Energy as an Investment Choice 

Grades 9-12, Economics 

* The Exponential Energy Centuly 

Grades 9-12, Science and Math 

*‘E’ 

the Magnificent Magician 

Grades NK-1, Science 

Energy: The Thread of Life 


Canada, Mexico and the United States: Energy 

Mix or Mix-up? 

Grades 6-9, Social Studies and Science 

Energy Conservation as a Political Issue 


Less Developed Countries and Energy 


Appropriate Technology for Energy Production 


Energy Flows in Natural Systems 


Critical Thinking on Energy 

Grades 9-12, English 

Energy Conservation: An International Comparison 

(United States, Sweden, West Germany, and 

Japan) 


Fossil Fuels and the Greenhouse Effect 


Energy and the Automobile 

Grades 9- 12, Science 

The Arithmetic of Energy Conservation 

Grades 4-6, Math 

Energy for Tomorrow 

Grades 5-7, English and Social Studies 

Exploring for Energy 

Grades 7-9, Science and Economics 

Making Decisions About Synfuels 

Grades 11-12, Science and Social Studies - 

150

Packet production 

United States 

PEEC differs from the large curriculum development projects of the sixties in several ways. 

Compared to the funding available to those efforts, the PEEC funding is ‘peanuts’. It was obvious 

to us from the start that we could not mount the full scale theoretical and practical development 

of ‘a curriculum’. We rely heavily on teachers as curriculum developers. The following production 

model has evolved. The PEEC staff chooses topics for summer packets. The topics are fleshed out 

with suggested lessons and are then the major focus of a steering committee meeting which 

develops the packet outlines further. We go into the summer writing session knowing more or less 

what packets we want to develop. We choose our teachers (from different grade levels and 

disciplines) with packet outlines in mind. We split the teachers into three writing groups which 

produce one packet each during the first two to two-and-a-half weeks of the writing session. 

The teachers then reassemble into two larger groups and produce two more packets. 

We do not completely dictate to our teacher-writers. We meet them at the opening session and 

discuss the five packet outlines with them, but still allow changes if they are sufficiently convincing. 

Many of the packets that are now in print or undergoing review and testing were not the 

packets we intended to produce. 

Distribution and implementation 

We believe that the PEEC materials can be used by teachers on delivery. In fact, of course, many 

teachers wil not pick up something new and use it in this way. Recognizing this fact, we have 

engaged - to the extent possible with our small staff - in workshop efforts as well. 

We have either sponsored or participated in twenty or more teacher workshops per year since 

the beginning of the project. In addition, we have put on workshops at the annual and regional 

meetings of both NSTA and the National Council for the Social Studies (NCSS). We have reached 

out to other educational organizations and have taken every opportunity to have our materials or 

a workshop leader or both at their conventions. 

We have also tried to make it possible for others to present workshops. For this reason, we 

have produced the Workshop Handbook which gives guidance to a local workshop leader who 

wants to put on a half-day or full-day workshop. 

Materials and workshops are a good start toward a project, but more is needed. We have 

publicized the existence of the materials and described our philosophy, etc. in journals and newsletters 

of both NSTA and NCSS. The need for a newsletter specializing in energy education was 

also soon apparent, and with partial funding from DOE, such a newsletter, Energy & Education, 

was born in the fall of 1977. Energy & Education is a bi-monthly publication. In its five issues 

per year, energy educators can find out what is going on and who is doing what around the 

country. Readers are given a calendar of events, a list of free and inexpensive materials, an 

editorial from someone with something to say to energy educators, book reviews of important 

energy books, and an energy facts page which keeps them up to date on data, etc. 

Energy h Education is in many ways our most important product. It is the one thing that 

gives a national image to energy education. It’s a way for the science teacher, the social studies 

teacher or the education manager of an electric supply company or an oil company to say to himself 

‘I belong to that group of people who call themselves energy educators’ and to keep up with 

what is happening in the field. 

The final step in the expansion of the early PEEC writing efforts into a full fledged project was 

to establish our Regional Energy Education Network (REEN). Since PEEC had grown in stature 

151


to a national project, it was clearly important for us to have communication channels to educators 

in various parts of the country. We needed to find out what was going on in energy education 

there and to let them know about and assist in their use of our materials. 

Early in 1978 we established a twenty-four-person Regional Energy Education Network. 

Twelve of the representatives were NSTA district directors, and twelve of them were social 

studies people in the same regions. REEN members have been, on the whole, quite active in their 

home regions. They have established workshops, they provided a distribution point for the PEEC 

materials and other materials, and they feed back to us their guidance for what is needed to make 

energy education work. 

Practitioners conferences 

Growth and the recognition of our national responsibilities caused us to branch out in one other 

direction. While Energy & Education serves as a satisfactory mass communication mechanism, 

we began to feel the need for meetings with the practitioners in the field who were teaching 

energy and, therefore, meeting the problems of implementing energy education materials head-on. 

With DOE funding, we held what we called the ‘First Annual Practitioners Conference on 

Energy Education’ at the University of Maryland in December of 1978. This first conference 

established the format that we’ve followed ever since. We divided the sixty to seventy participants 

into small working groups and asked them to summarize the state of the art in energy education 

for us and to make recommendations about its needs. 

The first conference was one in which internal communication and mutual support were 

extremely important. It was the first time that many people who had been involved in energy 

education in isolation in various parts of the country were able to come together, to share their 

concerns and to receive the support of others with similar enthusiasm. The first conference was 

reported in the January 1979 issue of Energy & Education. It seemed to have filled a need and 

early in 1979 we began to receive inquiries about holding the second conference and, with funding 

from a variety of sources, we held it at Rockford College in Rockford, Illinois, in late 1979. 

The effects of a year’s success were noticeable. The participants were more outwardly directed 

and their recommendations (which are available in a report from NSTA [ 201 ) essentially said to 

the school districts and state and federal agencies that ‘energy education is important and here’s 

what we need if we are going to continue it’. 

The upsurge of that confidence and growth were also evident at the Third Practitioners Conference 

held in November 1980 at the Tennessee Valley Authority’s ‘Land Between the Lakes’ 

conference centre. But members of this conference was not overconfident; they began to look 

very realistically at the future. The working group reports from that session (also available in 

a report from NSTA [30]) concern themselves with private and public co-operation, with guidelines 

for the search for funding, etc. It was already clear to us in November 1980 that the funding 

picture, which until that time had been largely federally based, was about to change. 

ENERGY EDUCATION - 198 1 

Energy education in 198 1 seems to have accomplished the difficult feat of reaching its apex and 

nadir essentially simultaneously. According to its sponsors, National Energy Education Day 

(NEED) was celebrated on 20 March in some 10,000 schools; proclamations were signed by 

forty-seven governors and several million students were made aware, at least for one day, of our 

152

United States 

energy situation. There was an International Conference on Energy Education sponsored by the 

University of Rhode Island in August, the Fourth Annual Practitioners Conference on Energy 

Education in October, and the first National Conference on Energy Education in Detroit in 

November. 

This national conference is the first attempt to treat energy educators as a professional entity. 

The response has been enthusiastic. The one day programme included concurrent sessions containing 

in all about seventy invited papers, contributed papers, or workshops. The conference was 

held simultaneously with the Annual Meeting of the National Council for the Social Studies and 

attracted, in addition to the social studies teachers, several hundred. science teachers, teachers 

from other disciplines and educators from the private sector. 

These outward signs of successful growth have been accompanied by the maturation of national 

materials development projects: NSTA’s PEEC, the DOE supported solar education projects at 

the State University of New York-Albany and the University of Southern California, and private 

efforts such as Energy and Man’s Environment (EME). New national efforts are gettidg underway 

- the ‘Energex’ project [22], supported by San Diego Gas and Electric Co., Westinghouse and 

ARCO, is a prime example. 

It is ironic that this year of high visibility coincides with a major change in thjk nature, and 

probably the level, of funding for energy education. Changes in the budget of DOE not only 

reduce the small budget of the Education Division from $5 million in 1981 to $1.7 million in 

1982, but more importantly, terminate the Energy Extension Service and the block grants - the 

State Energy Conservation Programme, for instance - which provided most of the funds which 

states used to fund energy education. And most states, having suffered revenue shortfalls in 1980, 

not only cannot pick up slack, but are also initiating further cuts. The large reduction in 1982 

funding for the DOE’S Conservation and Renewable Energy programmes will eliminate most of 

the money supporting solar energy education. All in all, federal/state support for energy education 

in 1981 wil be perhaps one tenth of its previous level. The remaining two to three million 

dollars of DOE education money is allocated mostly for faculty development and graduate level 

training programmes. 

These budget reductions have two complementary motivations. The present administration is 

committed to reducing federal spending. It views education as other than a federal responsibility 

and thus DOE’S mission-oriented education programmes were a tempting target. 

The reduction in the capabilities of groups like NSTA and the disappearance of the state 

energy education co-ordinators who were supported by the block grants leaves several questions 

whose answers will determine the future of energy education as an identifiable national endeavour. 

Questions 

1. Personnel support: With the reduction in federal and state support, who will provide the 

communication, co-ordination, planning and general leadership now provided by energy educators 

in State Energy or Education Agencies, and in national organizations such as NSTA, NCSS and 

the Education Commission of the States (ECS)? 

2. Networking: Where will support be found for the local, regional, and national meetings 

that allow energy educators to share experiences and make efficient use of multiple efforts? Wil 

there be support for a clearinghouse of energy education materials and resource people? Wil 

there be support for a newsletter? 

3. Teacher training: Where wil support be found for the teachers’ workshops which are so 

153


necessary to the introduction of a new topic like energy into the curriculum? Where will the 

knowledgeable staff come from? 

4. Materials development: How can it be assured that the broad range of viewpoints on the 

complex economic, environmental and social energy-related issues wil be incorporated into 

energy education materials? In an era of quick change, how can these materials be ke.pt up to date? 

5. Evaluation: Should the energy education materials made available to schools and teachers 

be evaluated as to accuracy, objectivity, and pedagogical effectiveness? Who should perform this 

function? 

We hope that the private sector, the electricity and gas supply companies, oil companies, coal 

companies and all the other companies whose major product or raw material is energy, will pick 

up some of the slack. There is some optimistic evidence to support this hope. The energy industry 

associations have all increased their activity. 

The private sector may provide the major support needed to answer the second question. NSTA 

and ECS [31] are circulating a joint proposal to API members for the establishment of a network/clearinghouse 

operation. Substantial funding for that effort has already been received. 

Even with unprecedented co-operation and support from the private sector, however, energy 

education is likely to change drastically in the coming years. There are areas in which the energy 

companies operate with little or no enthusiasm: the environmental and negative social impact 

of energy policy wil be difficult to present objectively; some industries wish to emphasize 

production over conservation; the nuclear controversy wil be difficult to handle in classroom 

materials; and questions 1, 3 and 5 above fall outside the usual pattern of private sector support. 

What wil happen? 

Energy education, like the energy situation itself, is going through a tumultuous transition in 

the United States. But energy education is well under way and thousands of teachers are participating. 

The new mood in the country, however, may cause it to quickly lose momentum as the 

federal push weakens. 

One of its weaknesses is a lack of professional identity. Coming from a variety of backgrounds, 

energy educators have not banded together to establish a political base. Maybe that is needed. 

Their identity is at present threatened by a DOE decision to reduce or even eliminate its support 

of Energy & Education. This newsletter to a large,degree is the central image-giving mechanism 

of the field. One test of the determination of American energy educators wil be to find out 

whether that newsletter can be supported by subscription. Such a test may be necessary. 

In addition to the lack of professional identity, there is a lack of evaluative baseline data. 

There are no general data on student knowledge or attitudes on the broad energy questions. 

There are no data on the percentages of teachers or schools seriously involved in energy education. 

There are no data on the impact of existing materials on student knowledge and attitude. Whether 

such studies wil be undertaken is one of the unanswered questions at this point. 

Success is always a possibility 

It may be that the task taken on by those who call themselves energy educators is nearer successful 

completion than we realize. It may be that we have already demonstrated to teachers that 

energy themes can fit easily into the curriculum in many places, Perhaps the examples that have 

been developed wil lead to a steady stream of both more and more sophisticated materials 

from teachers and textbook authors. 

154

United States 

Energy has two powerful advantages that may keep it alive in the curriculum even with the 

changes we have described in the funding and structure of energy education. 

The energy problem is perhaps, at present, the most crucial challenge to our species. 

It is pervasive and effects everything we do - and thus all that we teach about. 

At least we hope that science educators won’t forget it for a while, and that for our students 

energy wil never again be only that nebulous thing conserved in collisions of frictionless pucks 

and swinging pendula. Energy, viewed as the necessary input to biological cycles and industrial 

cycles; energy which is bought and sold and whose amount needs to be measured and whose 

quality needs to be both measured and maintained; energy whose availability affects national 

and international security, economic welfare, environmental quality and the quality of life itself, 

must provide an essential connection between science and all other disciplines. If this is achieved, 

energy education wil continue. 

REFERENCES 

1. HUBBERT, M.K. Energy From Fossil Fuels. Science, Vol. 109,1949, p. 103-9. 

2. AYRES, E.; SCARLOTT, C.A. Energy Sources: The Wealth of the World. New York, McGraw-Hill, 1952. 

3. FOWLER, J.M. Energy and the Environment. New York, McGraw-Hill, 1975. 

4. WILSON, R.; JONES, W.J. Energy, Ecology and the Environment. New York, Academic Press, 1974. 

5. ROMER, R.H. Energy: An Introduction to Physics. San Francisco, Calif., W.H. Freeman, 1976. 

6. DOOLITTLE, J. Energy: A Crisis -A Dilemma- Or Just AnotherProblem? Champaign, Ill., Matrix Publishers, 

Inc., 1977. 

7. DORF, R. Energy, Resources and Policy. Reading, Mass., Addison-Wesley, 1978. 

8. PENNER, S.S.; ICERMAN, L. Energy: Demands, Resources, Impact, Technology and Policy. Vol. 1,2nd ed. 

Reading, Mass., Addison-Wesley, 1980. 

9. RUEDISILI, L.; FIREBAUGH, M. Perspectives on Energy: Issues, Ideas and Environmental Dilemmas. New 

York, Oxford University Press, 1978. 

10. STOKER, S.; SEAGER, S.; CAPENER, R. Energy From Source to Use. Glenview, Ill., Scott Foresman, 1975. 

11. MULLIGAN, J.F. Practical Physics: The Production and Conservation of Energy. New York, McGraw-Hill, 

1980. 

12. PRIEST, J. Energy for a TechnologicalSociety. 2nd ed. Reading, Mass., Addison-Wesley, 1979. (physics text.) 

13. REYNOLDS, W.C. Energy from Nature to Man. New York, McGraw-Hill, 1974. (Engineering text.) 

14. BURBY, R.; BELL, A.F., (eds.). Energy and the Community. Cambridge, Mass., Ballinger Pub, 1978. 

15. MILLER, R.L. The Economics of Energy: What Went Wrong. Glen Ridge, N.J., Thomas Horton, 1974. 

16. ODUM, H.T.; ODUM, E.C. Energy Basis forMan and Nature. New York, McGraw-Hill, 1976. 

17. OPHULUS, W. Ecology and the Politics of Scarcity: Prologue to a Political Theory of the Steady State. San 

Francisco, Calif., W.H. Freeman, 1977. 

18. A catalog of such courses and programs has just been published: Schiff, ‘The Energy Education Catalog’, 

Academy for Educational Development, American Council on Education, 680 Fifth Avenue, New York, 

N.Y. 10019. 

19. CHRISTENSEN, J. Energy, Resources and Environment. Dubuque, Iowa, Kendall/Hunt, 198 1. 

20. LEIGHTON, P. Homesite Energy Systems. Hadley, Mass., Solar Plexus Press, 1981. 

21. Energy 80. mRD, J. editor. Enterprise for Education, Inc., 1981. (Enterprise for Education, 10960 Wilshire 

Boulevard, Suite 2134, Los Angeles, CA 90024.) 

22. Captain Power and Power Quiz. Energex Energy Education Programs, 1978. (Energex Energy Education 

Programs, P.0. BOX 7000-136,Palos Verdes, CA 90274.) 

23. Connections: A Curriculum in Appropriate Technology for 5th and 6th Graders. MELCHER, J., et al. National 

Center for Appropriate Technology, 1980. (NCAT, Box 3838, Butte, MT 59701.) 

155


24. FOWLER, J.M. Energy Environment Source Book. Washington, D.C., National Science Teachers Association, 

1980. (Available from NSTA, 1742 Connecticut Avenue, N.W., Washington, D.C. 20009. Order prepaid, $6.50.) 

25. Energy Conservation in the Home. An Energy Education/Conservation Curriculum Guide for Home Economics 

Teachers. Prepared by the University of Tennessee Environment Center and College of Home Economics, 

Knoxville, Tenn., for the United States Department of Energy, October 1977. 

26. The Energy Educators Forum is composed of representatives from the American Gas Association (AGA), 

American Petroleum Institute (MI), Atomic Industrial Forum (AIF), Edison Electric Institute (EEI), and 

National Coal Association (NCA). 

27. Energy Education Materials Inventory, Vols. I and 11. An Annotated Bibliography of Currently Available 

Materials, K-12. Prepared by Energy Institute, University of Houston for the United States DOE, Assistant 

Secretary for Intergovernmental and Institutional Relations, Office of Education, Business and Labor Affairs, 

August 1979. 

28. NSTA/DOE Fact Sheets on Energy Technologies; a set of 19 were published in 1977 and a new revised set of 

20 are awaiting DOE clearance and printing. 

29. HOFMAN , H.; MILLER, F.G. (eds.). SecondAnnualPractitioners Conference on Energy Education. Washington, 

D.C., National Science Teachers Association, 1980. 

30. WHITE, J.A.; HOFMAN, H. Third Annual Practitioners Conference on Energy Education. Washington, D.C., 

National Science Teachers Association, 1981. Proceedings of the Second and Third Conferences are available 

from National Science Teachers Association, 1742 Connecticut Avenue, N.W., Washington, D.C. 20009. 

31. The Education Commission of the States (ECS), ‘a nonprofit organization formed by interstate compact to 

further working relationships among governors, state legislators, and educators for the improvement of 

education at all levels,’ has also been engaged for several years in efforts to further energy education. 

156


Introductory statistical physicsl: a comparison of several 

ways of introducing elementary statistical mechanics 

J. OGBORN. 

‘Anyone who has tried to present a rather abstract scientific subject in a popular manner knows 

the great difficulties of such an attempt. Either he succeeds in being intelligible by concealing the 

core of the problem and by offering the reader only superficial aspects or vague allusions, thus 

deceiving the reader by arousing in him the deceptive illusion of comprehension, or else he gives 

an expert account of the problem, but in such a fashion that the untrained reader is unable to 

follow the exposition and becomes discouraged from reading any further. ’ 

A. Einstein. 

APPROACHES TO STATISTICAL PHYSICS 

This paper gives a comparative analysis of the conceptual structure of a number of different 

approaches to the introductory teaching of statistical mechanics and attempts to identify a small 

number of crucial features which lie behind the problems into which each approach runs. 

FEYNMAN 

Strategic problems 

It happens that the approach in The Feynman Lectures (Feynman et al, 1963) shows up many of 

the dilemmas that face one in attempting to construct a simple but deep programme of teaching 

about the statistical basis of thermodynamics. The principle dilemmas are: (1) whether to 

emphasize the independence of macroscopic, phenomenological thermodynamics from microscopic 

models of any kind or whether to use insights from microscopic models in developing 

macroscopic ideas, at the risk of making the macroscopic seem to depend on the microscopic; 

(2) how to convey the general application of thermodynamic ideas and arguments, and not make 

them seem special to the systems discussed; (3) given a decision to use microscopic models, how 

1. Edited version of a paper presented to the GIREP conference, Montpellier, 1976. Reprinted, with permission, from Delacbte, 

G (ed.), Physics Teaching in Schools, London, Taylor & Francis, 1978. 

157


to deal simply and effectively with statistical arguments - this involves choosing the best systems 

to consider, the kind of statistics to emphasize and the mathematical resources to use; (4) how to 

trade rigour against intuitive understanding (and working out what the latter means in this context); 

and (5) just what physical systems, or types of systems, to emphasize (engines, electrochemical 

cells, vapours etc.). 

Feynman shows that he is aware of many of these problems: ‘it is a difficult subject and the 

best way to learn it is to do it slowly. The first thing is to get some idea, more or less, of what 

ought to happen in different circumstances, and then later. . . we wil formulate it better.’ On the 

macroscopic - microscopic dilemma: ‘The deepest understanding. . . comes. . . from understanding 

the actual machinery underneath, and that is what we shall do: we shall take the atomic 

viewpoint from the beginning, and use it to understand the properties of matter and the laws of 

thermodynamics.’ On the classical/quantum dilemma (what statistics to use) ‘. . . many things 

that we wil deduce by classical physics wil be fundamentally incorrect. . . however, we shall 

indicate in every case when a result is incorrect.’ 

Feynman offers an important insight into this last dilemma when he writes: ‘It turns out that. . . 

although most problems are more difficult in quantum mechanics than in classical mechanics, 

problems in statistical mechanics are much easier in quantum theory.’ The reason is that in 

quantum theory one can count: states become discrete instead of continuous, so that integrals 

turn into addition sums. 

Feynman’s decisions about many dilemmas are clear. He firmly emphasizes microscopic interpretations. 

His statistical arguments are as simple as they can be made: no permutations or 

combinations are used at all. All the arguments concern Maxwell-Boltzmann statistics, though 

he takes opportunities to demonstrate the failure of classical statistics. He chooses a clear focus 

for argument in the Boltzmann factor, a choice enabling him to illustrate the wide variety of 

applications for the ideas. 

A remarkable and novel chapter on the ratchet and pawl as a heat engine attempts to link the 

otherwise quite distinct macroscopic and microscopic sets of arguments. The key to understanding 

the nature of his approach is its selectivity. Figure 1 shows just how selective it is, as it 

indicates how few of the topics discussed by others are picked out by Feynman. 

Choices amongst statistical arguments 

Any decision to offer a statistical approach hinges on finding some simple treatment of the 

statistics. Feynman finesses the problem. Rather than do statistics, he treats a clearly statistical 

problem in a non-statistical style, choosing to look at the exponential distribution with height 

of the density of an isothermal gas, from which he extracts the Boltzmann factor. 

The exponential atmosphere 

Feynman’s neat trick is to produce the simple argument that in an isothermal atmosphere in 

equilibrium in a gravitational field, the density, and so the ratio of the numbers of molecules 

per unit volume at different heights, is given by 

n/n, = exp(-mgh/kT) 

He argues that there must be a difference of pressure across any small interval dh, just sufficient 

to support the weight of the gas in that interval, so that 

158


dp = -nmg dh 

m being the mass of one molecule. The rest follows using kinetic theory. 

Feynman then presents this result, not as a special case but as an instance of a general result 

n = constant exp(-E/kT) 

in which exp(-E/kT) is the Boltzmann factor with mgh generalized to any appropriate potential 

energy difference. 

Figure 1 shows how Feynman’s strategy works, After an introduction on random walks to 

introduce statistical distributions, the exponential atmosphere argument is used to go straight to 

applications of the Boltzmann factor, of which he gives several varied examples. But nowhere 

Exponential 

atmosphere 

Boltzmann 

factor 

ll 

Reversible and 

i rrevers i b le 

processes 

Chance 

State, distribution 

Einstein solid; Boltzmann factor; 

Mixing W,,, 

Q‘/Q =N/n 

c a I cu lat io n by 

permutation unit change 

quantum shuffling 

Isothermal 

expansion 

AlnQ=Nln2 

A S =NRTA 1nV 

Entropy: use of 

numerical values 

I 

Uses of Boltzmann: 

vapour pressure 

Uses of entropy: 

equilibrium 

meltlng, evaporation 

engines. cycles 

statistical 

Figure 1. Feynman’s introductory method. 

159


do arguments about changes in numbers of microstates appear, nor is dS = kd (In a) to be found. 

Is he then ‘doing statistical mechanics’? Yes, in the sense that the Boltzmann factor contains the 

statistics. No, in the sense that it is not clear how it does so. 

Feynman can finesse the statistics, because of the form common to all the applications he 

discusses, indeed to any. Briefly, any process that borrows energy E from a heat bath involves 

an entropy decrease of the heat bath of AS = - E/T (leaving aside qualifications about constant 

volume etc.). Writing this as A In 52 = - E/kT, and A In 52 as In ( after/a before) we always get 

The ratio of the values of 52 after and 52 before borrowing energy E gives the probability that it 

can be borrowed, and so the numbers of particles able to borrow that much energy. Thus the 

Boltzmann factor works because it is a ratio of numbers of microstates. 

The finesse shows up in what looks like a trivial point in Feynman’s argument. The gas must 

be isothermal, so he introduces a ‘copper bar’ to keep it so (figure 2). Now of course the Boltzmann 

factor does not just apply to gases under gravity (the examples Feynman uses are to show this). 

So the argument is not really involved with the system being a gas, even though it appears to be 

all about that. The ‘copper bar’ is what does the trick. The energy rngh for a molecule to get up a 

height h cannot come from the gas if the gas must not become cooler in any part. It must come 

from the ‘copper bar’ heat sink; indeed, this is just what a canonical ensemble argument relies 

on. There are fewer molecules at great heights because the sink is unlikely to yield up that much 

energy by a chance fluctuation. There are fewer molecules at great heights because the ones 

below must hold them up, too, but the two ‘becauses’ are very different. The first is an essentially 

statistical mechanical argument; the second is particular and ad hoc. Feynman uses the second 

and not the first, and so is unable to show why the result he gets is general, not special. 

- 

Mechanism 

for equalizing d 

temperatures. 

h 

Feynman’s ‘copper bar’ to maintain gas 

isothermal state 

Figure 2. Feynman’s ‘copper bar’ to maintain gas in isothermal state. 

Feynman and heat 

In speaking of the second law, Feynman says things like, ‘. . . it ought to be possible to lift 

weights. . . and thus to do work with heat’; ‘If the whole world were at the same temperature, 

160


one could not convert any of its heat energy into work’; ‘. . . if we could obtain work by extracting 

the heat out of the ocean’. Such remarks can only be read as speaking of heat as the energy 

inside things. Feynman is perfectly aware of the difference between heat and internal energy, 

and frequently draws all the necessary distinctions. But it is, I think, a property of many 

approaches to statistical mechanics, which emphasize particular microscopic models, that they 

tend to make it natural to blur the distinction: to talk at one moment of heat as flowing under a 

temperature difference and at another of heat as internal energy, usually ‘random’ in some 

sense. Indeed, in the exponential atmosphere argument, one is left with some impression that the 

molecules climb the gravitational hill at the expense of the ‘random’ internal energy or heat in 

the gas. 

What is the Feynman’s temperature scale? 

Feynman offers the excuse to raise another matter. 

In the expression exp(- EIkT), what is T? In his approach to the Boltzmann factor, it appears 

that T is the temperature on the ideal gas scale, because the argument derives from the gas laws 

and kinetic theory. More fundamentally, of course, it is not that at all, but is a temperature 

defined statistically ; defined by a relation of the form 

T = E/kA lnn 

in which k functions, not as R/N, but as an arbitrary scale constant linking an energy E and a 

change in the logarithm of a number of microstates to the Kelvin scale on which the triple point 

of water has a chosen value. 

Of course the ideal gas temperature is the same thing, but it is the same because of what ideal 

gases are, not because of what temperature is. Similarly k = R/N because of the nature of ideal 

gases; the relation says nothing about k. 

THE PSSC’ APPROACH 

The PSSC Physics: Advanced Topics Supplement (1 968) and College Physics (1968) propose a 

quite different, equally radical and equally simple approach, now mainly focused on the second 

law from a statistical point of view. 

The overall strategy 

The PSSC strategy is startlingly simple. Perhaps the easiest case of all to argue statistically is that 

of the spreading out of N independent particles into double the previous volume. Arguing that 

each has a probability of 50 per cent of being by chance in the original half, the probability that 

all the particles wil so do is YP or 2-N. The logarithm -N In 2 of this quantity appears in the 

expression NkT In 2 for the work done in changing the volume (isothermally). In this case, the 

work done is equal to the heat exchanged with a heat sink, so 

AQ = NkT In 2 

1. Physical Science Study Committee. 

161


It then becomes possible to name AQ/T the entropy change, and identify it with Nk In 2, that is, 

with k times the change in the logarithm of the probability. 

The approach exploits the simplicity of two arguments - first, the statistics of particles in two 

halves of a box and, second, the work done in isothermal expansion of a gas - to link entropy 

seen as to do with chance to entropy measured with heaters and thermometers. The latter can be 

seen then as a way of doing statistics without doing statistics: macroscopic entropy changes can 

be used to compute microscopic changes in numbers of states. This is one virtue of the PSSC 

approach. In this way, it resolves the link between microscopic and macroscopic. The first is 

presented as fundamental, but usually impracticable as a means of computing, while the second 

is presented as convenient and practical, but to be understood in terms of the first. 

Exponential 

atmosphere 

Boltzmann 

factor 

irreversible 

Random motion 

Chance 

Einstein solid; Boltzmann factor, 

Chance 

State,distri bution 

Diffusion 

b 

R 

c a I cu I at ion by 

permutation unit change 


Isothermal 

expansion 

31nR =Nln2 

AS=NkTAlnV 

Entropy: use of 


Uses of Boltzmann’ 


thermi onic em ission 

conduction 

rate of reaction 

ionization 

I 

Uses of entropy : 

equili br ium 

melting I evaporation 

engines, cycles 

Second law 

statistical macroscopic 

Figure 3. PSSC method. 

162


Counting states in one system using another 

Fundamental to the PSSC approach is the attribution of the change in the number of microstates 

to the heat bath. This raises a number of new issues and has important consequences for the rest 

of the structure of the PSSC teaching programme (see figure 3). 

Having argued that the change in In 52 (though they use ‘probability’) of a gas is NkT In 2 

when it doubles its volume isothermally, they need to find a way of saying that the same change 

of In 52 occurs in the heat bath that delivers heat AQ to the gas, so that the value of AS that 

really matters, that of the heat bath, is brought out. The point is that the entropy change of the 

gas is easy to calculate but is not what is wanted; while that of the heat bath is hard to calculate 

and is what is wanted. 

The trouble is that AQ/T is only equal to NkT In 2 if the change is reversible. PSSC thus have 

two major problems: to explain what a reversible change is; and to explain why, in a reversible 

change, 52 for the whole system is unchanged so that changes in 52 for the two parts of it are 

equal and opposite. As with Feynman, these problems arise out of trying to do statistics without 

doing statistics (or doing, as here, very little). 

PSSC’s reversible and irreversible oscillations 

It cannot be said that PSSC’s solution to the necessity to say what reversibility is lacks ingenuity 

(figure 4). A filmed demonstration (Ferretti) shows gas being made to oscillate in volume, by 

being coupled to an inverted pendulum. The decay of free oscillations is studied, with varying 

amounts of aluminium foil surface exposed to the gas, so that oscillations are nearly adiabatic 

(no foil), nearly isothermal (much foil) and in between. At the two extremes, the damping is 

least, so suggesting that isothermal and adiabatic changes could both be reversible. 

VY 

masses 

rnerr 

vo- 

Figure 4. PSSC gas oscillator. 

Figure S. PSSC marble machine. 

Necessary and unnecessary statistics 

The PSSC strategy not only needs reversibility and irreversibility, but it needs to present them 

statistically. This they do mainly through the use, again on film,of another special pedagogic 

device, the marble machine (figure 5). The marble machine is a pair of channels which can carry 

marbles, each leading to a larger space with a gap between the two, all mounted on a tilting 

board. If marbles are started in one channel, they slowly become distributed between the two, 

as the board is tilted many times. Conceptually, much hinges on the machine. It has to illustrate 

163


that the random process of interchange reaches, and then does not depart from, an equilibrium 

distribution in which there are (with fluctuations) equal numbers in both channels. It is used to 

distinguish the concepts of state and distribution; that is, respectively, which marbles are in 

which channel and how many are in each. The distinction is used to show, using the binomial 

distribution, that the equilibrium distribution has more microstates than non-equilibrium 

distributions. 

The use made of it to consider the distribution with the greatest number of microstates brings 

us to another question of great strategic importance. Many textbooks of the kind that make no 

concessions use the method of undetermined multipliers as a general tool for calculating entropy 

changes statistically, obtaining the distribution with the maximum number Wmax of microstates. 

The ratio of two values of W,,, is then taken to be a good approximation to the ratio of 

the corresponding values of S2, the total numbers of microstates the system has access to under 

given constraints. Strategically, one needs to choose the line of argument which maximizes W, or 

the one which calculates a. Concretely, in the present instance, S2 increases by the factor 2N 

when the marbles are allowed to go into one empty half, or‘does so by the same factor when the 

gas spoken of expands to twice the volume, if the molecules are far enough apart to treat them 

as if they were distinguishable, even though they are not. W is more complicated. In general, if 

there are N marbles, NI in one half and N, in the other, 

W=N!/N, !N2! 

with W,,, = N! /(N/2) !(N/2) 

! (N is even, or large). 

It was clear before that only 

before = 2N is needed, so PSSC did more than they 

needed to. Further, the calculations with W are the more complicated of the two, and this turns 

out to be true of a variety of the systems discussed in connection with other approaches. There 

can be no doubt that S2 is more fundamental; the problem is making it easier to deal with in 

calculations. Certainly the factor 2N offers little trouble, containing only one basic notion: that 

independent numbers of ways multiply, an idea of fundamental importance to thinking about the 

whole subject. 

‘Inexorably, quite by chance’ 

The PSSC film Random Events widens the range of issues under consideration. Most of all, it 

tackles one of the hardest psychological problems of a statistical approach: that of seeing the 

inevitable as happening by chance. That is, all macroscopic processes involve large numbers of 

particles, so that the tendency to statistical equilibrium involves so large an increase in S2 that 

it is ‘certain’ to happen. 

GURNEY’S APPROACH 

The first few chapters of Gurney’s Introduction to Statistical Mechanics (1 949) have influenced 

several others (Bent, 1965 ; Millen, 1969; Powles, 1968; Sherwin, 196 1 ; Spice, 1968) (though 

some of them may have re-invented the approach). Gurney made two influential choices. First, 

he chose to discuss, not gases as most others had done, but the Einstein solid, Second, he used a 

neat device for avoiding Lagrange multipliers, which turns out to have a number of virtues 

and uses. 

164

Use of the Einstein solid 


The value of the Einstein solid is that its weakly coupled oscillators have equally spaced energy 

levels (non-degenerate) so that the distribution of energy amongst oscillators follows the Boltzmann 

factor exp(-E/kT). In general, a system with unequally spaced energy levels wil have 

quantum states populated according to exp(-E/kr), but where there are many levels within 

a narrow range of energy dE, the number of particles having energy in that range wil be larger 

on that account (figure 6). 

Energy states 

Energy E 

0 

U 

m 

'4- 

0 

L 

a, 

D 

E 

a, 

ol C 

m 

L 

C - 

z' - 

Energy states - 

Gas-like svstern 

Energy E 

Figure 6. States and energy distributions. 

Any classical system wil thus have an energy distribution with two terms in it 

N(dE) = f(E) exp(-E/kr) dE 

The first term f(E) results from the number of states in intervals dE at various energies E, and 

comes from quantum mechanics. It has nothing essential to do with statistical mechanics. The 

second term is the statistical-mechanical one, and is the one which appears alone and unencumbered 

in the distribution for the Einstein solid. A minor point is that the sites of oscillators 

are distinguishable, even though the oscillators would not be, so that Maxwell-Boltzmann statistics 

is sufficient. The next section describes Gurney's other choice. 

Unit changes 

Gurney adopts the line of argument which maximizes W, but introduces a neat way of doing it. 

For the Einstein solid 

w =N! /no!n1 !n2!. .. 

165


The problem is, what values of the numbers no, nl, n2 etc. of particles (total N) in the various 

levels maximize W? At the maximum, a small change must leave W the same. Such a change is 

to promote one particle one level, say from the i th to the j th, and keeping the energy constant, 

to demote another, say from the q th to the p th. Now adding I to n multiplies n! by the factor 

n+l; taking 1 away divides it by n. If n is large n+l is nearly equal to n. So the effect of the 

promotion is to multiply W by nj/ni; of the demotion to multiply it by nq/np. If W is to be 

const ant : 

or 

(nilnil = (np lnq 

Since the pairs of levels are arbitrary, the numbers in any pair of successive levels must all be in 

the same ratio. It follows that the distribution must be exponential. 

Unit change arguments of this kind are very useful. We used them in the Nuffield Advanced 

physics work on thermodynamics, and I have used them in an argument about the normal 

distribution (Ogborn, 1974). They are of general use because all combinatorial problems lead to 

expressions for numbers of states which are long strings of products, because numbers of ways 

multiply. A unit change (adding a particle, adding a quantum of energy, interchanging particles) 

wil thus always multiply W and i2 by some factor. The expression for this factor wil be simplier 

than the factorial expression it modifies. Further, it is nearly always changes to systems, and so 

to W or i2, which are of interest. 

The arguments for the multiplying factor resulting from a unit change are the same as those 

for W or i2 and can sometimes be used directly to get the multiplier without evaluating W or 52 

at all. But the method then involves an important conceptual difficulty. Often, a unit change 

alters terms like no, n1 etc. above, which divide the expression for W (or a), and which appear 

because the objects concerned are not distinguishable. The trouble is that the reason for these 

terms is the hardest part of the statistics to explain simply. 

Sometimes it can be done. Consider a simple ‘reaction’ in which objects of type A change to 

ones of type B (applicable to instances like defects in solids, changes in state etc.). In the extreme 

case when just one particle is of type B, a list of the particles looks like: 

AAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAAAAAAAAA 

and it is clear that there are as many possible lists as objects. Convert the one B to an A and there 

is just one list: 

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA 

The effect of changing one particle from a B to an A is to reduce the number of re-arrangements 

by the factor N, the number of objects. Generalizing, the factor wil always be equal to the 

number of A objects after the change, NA . The fact that there was only one B particle concealed 

another effect. If all were B particles: 

BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 

and one became an A, there are now many possibilities, such as: 

166 

BBBBBBBABBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB


Exponentia I 

atmosphere 

Boltzmann 

factor 


irreversible 

processes 

Chance 

State. distribution 

chance 

Diffusion 

2N 

Einstein solid, Boltzmann factor, 

Wma, 

calculation by 

permutat ion 

Mixing wwx 

SZ'ISZ = N/n 

Isothermal 

expansion 

Aln SZ = Nln2 

A S = Nk TA 1 n V 

Entropy use of 


Uses of Roltzmann. 


thermionic emission 

conduction 


ionization 

ri 

Uses of entropy. 

equilibrium 

melting, evaporation 

engines. cycles 

Figure 7. Gurney and Sherwin methods. 

The number is now multiplied by the number NB of B-objects there were before the change, in 

general. So if in a mixture of NA A-objects and NB B-objects, one particle changes from B to A, 

the net effect on the number of ways is to multiply it by the factor NB IN*. The argument can be 

extended to chemical equilibrium (Bent, 1965) and to all those problems of the same kind as the 

dissociation of water into ions, and so on. 

The argument is no more than a verbal version of the argument which establishes the factorials 

in expressions for W or a. Whether such arguments, though longer, are easier than the more compact 

and usual algebraic form is not easy to decide. But the change discussed is a relevant physical 

167


change to a system, which can be imagined happening, not a formal play with permutations 

(though above it was cast in a generalized way, it need not be). Incidentally, it avoids the use of 

Stirling’s approximation as well. 

Distributions: most probable and average 

As we saw, Gurney uses Wmax and so the most probable distribution; not S2 and the average 

distribution. This creates the problem that sooner or later he and others who take that approach 

have to argue that A In Wmax A In S2, since they really need AS = k In S2. 

More seriously, as Gurney himself brings out very well, it is only changes in 52 in an interacting 

system that have any interpretation. That is, if parts X and Y of a system are independent, then 

‘X = ’ total 

but the same is not true for W,,,. Thus even to introduce temperature on Gurney’s approach 

(through thermal equilibrium between two systems), S2 has to be used. 

Variations on Gurney 

Powles extends the informal introductory use of Gurney’s arguments by numerical examples 

(Powles, 1968). He calculates by enumerating states the most probable and the average distributions, 

going so far as to calculate the specific heat capacity of a five-oscillator Einstein solid. Such 

examples seem likely to be of considerable value in developing an intuitive idea of the subject, 

and must be welcome in a topic nomially ridden with algebra and short on reality. 

Sherwin offers a much more radically worked out version of Gurney’s arguments, also (unlike 

Powles) exploiting the unit-change method. Like Powles, he uses extensive numerical examples, 

enumerating states. In these examples, temperature is given a qualitative statistical sense, as a 

measure of the probable direction of spontaneous energy flow, since the examples include two 

systems coming to thermal equilibrium. 

He also uses W, rather than CL, and this means that he has to do a difficult sum over an 

infinite number of exponential terms to obtain the specific heat capacity. This calculation is 

much easier with S2 (cf Bent 1965, Nuffield Advanced Physics, 1972). However, it is in Sherwin 

that one major advantage of the Einstein solid is clear. Given that the arguments lead to an 

exponentially graded distribution, temperature can be introduced as related to the gradient: 

the hotter the solid, the shallower the grading, so T appears as a divisor in exp(-E/kT). 

BENT’S APPROACH 

Bent deserves a discussion of his own, because, although like Gurney he uses the Einstein solid 

and unit-change arguments, he uses them to operate on S2 rather than Wmax, and because he 

offers a total pattern of teaching which has flair, is distinctive, and has some rare merits. 

The boxed parts of figure 8 show Bent’s statistical arguments, to be compared with figure 7 

(Gurney). He has a unique, if not totally convincing, argument by induction from small numbers 

to the expression 

S2 = (N-l+q)! /(N-l)! (q)! 

168


for the total number of microstates of N oscillators sharing q quanta. Now the unit change 

method gives, if one quantum is added, a multiplier of (N+q) and a divider of (q+l). As q+l x q 

this at once gives (N+q)/q for the factor multiplying S2 when one quantum is added, or dividing 

it when one is taken away. As argued before, the multiplying factor is much simpler than the 

thing it multiplies. 

E xponenti a I 

Reversible and Chance 

atmosphere ir reversi ble State, distribution 

Boltzmann 

processes 

factor 

Random motion 

chance 

Diffusion 

2N 

Isothermal 

expansion 

Aln n=Nln2 

AS=NkTbInV 

Uses of Boltzmann 


therm ionic emission 

conduction 


ionization 

melting. evaporation 

Figure 8. Bent’s method. 

Bent has previously introducedS= k In S2, by announcement, not argument. Also he has defined 

T = dU/dS at constant volume 

so that when one quantum of energy E is transferred, 

169


from which it follows that: 

1 +N/q = exp( e /kT) 

and from which the energy per oscillator, e/exp(e/kT)-l follows. But Bent does not show what 

is clear from the last equation, that 1+N/q is equal to the Boltzmann factor (its reciprocal), so 

giving the ratio of the numbers of oscillators differing by energy E. 

The argument can get added value by being stood on its head, exploiting the fact that the 

ratio 1+N/q is equal to the ratio s2 after/s2 before, thus to ratios of oscillators in different levels, 

but also to the temperature in a fundamental way, taking the equation 

as a special case of the general relation 

T = E/k In (I+N/q) 

T= elk Aln 52 

In the absence of such an argument, Bent has to fall back on the well known argument via 

maximizing W, discussed earlier. 

Configurational entropy changes 

Bent makes good use of the unit change method, starting from the binomial expression for W, 

to obtain results essential to chemistry. These concern the fact that, extending the argument 

given under ‘Unit changes’ above, he considers one particle added to a mixture. If the mixture 

previously contained a mole fraction n/N of particles like the one added, 52 is multiplied by 

N/n by adding another one. Thus for one extra particle, AS = -k In n/N, and for L extra particles, 

AS = -L k In n/N = -R In n/N. 

This provides the basis for a discussion of chemical equilibrium (e.g. why water dissociates 

a little because, despite thk great entropy change against it, the first molecule to dissociate 

produces a large entropy change just by becoming ions different from the other particles they 

are mixed with). 

Entropy by numbers 

Physicists can learn from chemists that entropies of things have actual numerical values that 

make sense. Chemists use tables of values to make predictions; physicists often do not have 

the least idea of the value of any entropy or entropy change at all. Bent, a chemist, uses numerical 

values with great verve: ‘Science, it has been said, begins in observation. The best way to become 

aquainted with birds, for example, is to look at some birds. A good way to become acquainted 

with entropy is to look at some entropies.’ (Table 1). 

170


TABLE 1. Some entropies 

Molar entropy at room temperature 

atmospheric pressure / JK-’ mol-’ 

diamond 

platinum 

le ad 

laughing gas 

2.5 

42 

65 

220 

These numbers suggest that entropy is related to hardness. Indeed, as a rule hard gem-like abrasive 

and refractory materials such as diamond, garnet, topaz, quartz, fused zirconia, silicon carbide, 

and boron nitride, in which the individual atoms are bound to each other in nearly infinite three 

dimensional lattices by genuine chemical bonds that severely limit random thermal motion, have 

small measured entropies.’ Bent goes on to discuss gases, melting, evaporation and the closeness 

of the entropy of water of crystallization to that of ice. 

Qualitative discussions of this sort are not uncommon (Angrist and Hepler 1967, Open 

University, Course S 100, 197 1). Nor are formal logical accounts. What is unusual is Bent’s inbetween 

tactic: quantitative but not deductive, intuitive but not vague or evasive. 

SOME FEATURES OF THE BERKELEY APPROACH 

Not all the features of Reifs volume Statistical Physics (1965) in the Berkeley series can be 

looked at here. But, like Gurney, the tough body of the book is introduced by one or two 

preliminary chapters of considerable inferest. 

Using computer simulation 

Reifs first two chapters exploit the technique of computer simulation which others have also 

used: (Alder and Wainwright, 1959; Nuffield Advanced Physics, 1972; Open University Course 

T100, 1972; Reynolds, 1965). Of course, similar Monte Carlo methods are a significant research 

tool, for example in the thermodynamics of polymers (Hammersley and Handscombe, 1964). 

Reifs system is a set of classical particles moving in a box. Four, and then forty, particles are 

followed as collisions take them from one half of the box to the other. Numbers in each half, 

and the proportion in each half, are followed, showing how absolute fluctuations increase with 

numbers, but that relative fluctuations decrease. The exercise is directly comparable with the 

PSSC marble machine, and with similar data from the motion of pucks on an air table (Nuffield 

Advanced Physics, 1972), and with a dice-throwing paper simulation (Nuffield Advanced Physics, 

1972). The purpose is the same: to illustrate the ideas of microscopic state and distribution; 

their differences; and how a system of many particles wil tend to an equilibrium distribution 

subject to fluctuations but approximating well to stable deterministic behaviour. 

Like the PSSC machine, Reif uses his model to show the irreversible nature of the change 

towards equilibrium, with the added interest that the motions in his system are all precisely 

reversible, being Newtonian motions of elastic particles. He is thus able, by reversing the motions 

and making the system ‘evolve backwards’, to pose the reversibility paradox in an acute form. 

In the Nuffield advanced physics course, similar ideas are tackled by using film of real events 

run both forwards and backwards. 

171


A different computational approach is used by Reynolds (Reynolds, 1965; see also Open 

University, Course TI 00, 1972). He uses an artificial system of ten particles each with access to 

five equally spaced energy levels, so that all possible distributions (there are 23) and all possible 

microstates (there are 72 403) can be enumerated. The computer is given appropriate transition 

probabilities, and then follows the system to equilibrium, showing that there is a stable equilibrium, 

with the system spending time in each distribution proportional to the number of microstates it has. 

Two-state systems 

In chapters 2, 3, and 4 Reif exploits to some degree the valuable isomorphism between such 

different examples as particles in two halves of a box and two-state systems such as a paramagnetic 

solid. The arguments above (Unit changes, pp. 165 et seq) about mixtures are also of the same 

form, giving a whole class of useful simple problems which are physically different but use the 

same simple analysis. Reif does not use the unit-change method in his account of paramagnetism. 

If one does, it becomes quite simple. Regarding the two states (parallel or antiparallel to the field) 

as A and B states as before, a transition from B to A changes 52, with 

52 after 152 before = NB /NA 

If energy e is borrowed from a heat bath for the transition, there is another change to Cl: 

so that the equilibrium value is 

52 after/n before = exP(*/kr) 

NB INA = exp(e/kr) 

- 

Putting E = 2pB, and the magnetization asp (NB-NA) 

yields the usual results for a paramagnetic 

solid, and the Curie law as a good approximation at small pB/kT. 

The same style of discussion serves to handle such problems as the proportions of Zuevo and 

dextro forms in a sugar, the ionization of a gas or of water, and so on, with minor modifications 

each time. 

THE NUFFIELD ADVANCED PHYSICS APPROACH 

The Nuffield Advanced Physics (1972) approach reflects many of the conclusions that seem to 

me to follow from the previous analysis. 

First, informal, intuitive teaching of the sort examplified by Bent is likely to be important. 

In the Nuffield course there is a good deal of it: film shown forwards and in reverse; simulations 

using dice; and (with other values of its own) discussion of fossil fuel resources. We also borrowed 

from Bent the idea of using numerical values of entropies. 

Second, arguments using the total number of microstates 52, getting from changes to 52 an 

average distribution, have advantages over the more usual calculation of the number of states 

W,,, in the most probable distribution. The latter is less useful in the end, and involves more 

work. In the Nuffield work we only use 52. 

Third, calculations using unit changes offer an important simplification, and can even avoid the 

need to calculate 52 (or W,,,) at all, since ultimately only changes to them are of interest. But 

172

~~ 

Exponential 

atmosphere 

Boltzmann 

factor 

- 


i r reve rs i b le 

processes 


C5ance 

State, distribution 

Random motion Diffusion 

chance 2 N 

11 

Einstein solid; Boltzmann factor 

a 

W,X 

calculation by 

permutation 

unit change 


Mixing w,,, 

a’/ n = N/n 

lsother ma 

I 

expanston 

A ln!2=Nln2 


thermionic emission 

conduction 


ionization 

Second law 

st,at i s t i ca I mac r osc opl c 

I 

Figure 9. Nuffield ‘Advanced Physics’ method. 

the arguments are subtle and difficult for students to understand, and need great care. However, 

they do show the deep importance of multiplicative factors, and so why entropy is defined 

logarithmically, with A In s2 being almost always an easier quantity to handle than any other. 

Fourth, the Einstein solid, the main example in the Nuffield approach, is a very valuable object 

to discuss, since the Boltzmann factor is not compounded with a density of states (classically, 

phase space) factor. It also illustrates that, as Feynman says, sometimes quantum physics is easier 

than classical, because in quantum physics one can count. 

Fifth, computer simulations, as used by Reif and others, can play an important role. In the 

Nuffield work, we used a computer-made film of a Monte Carlo simulation of an Einstein solid 

reaching equilibrium. A special advantage of visual output, such as Reif‘s or the Nuffield film, 

is that fluctuations come alive in the argument, with the movie version probably having the 

advantage here. 

173


Sixth, whatever one’s approach, the generality of thermodynamics is probably better brought 

out by a variety of examples of its uses, of as many kinds as possible, than by casting the argument 

in abstract, generalized terms. But different examples needing different statistical calculations 

would introduce difficult distractions, so that families of examples (such as two-state and allied 

systems) with the same basic calculation for all offer advantages. 

Seventh, the Boltzmann factor is the pivot around which applications turn, so that the sooner 

one can get to it the better. But here Feynman illustrates that there is a choice to be made 

between getting it in an ad hoc way, or getting it in a way that shows that it is a ratio of numbers 

of microstates in a heat bath. In the Nuffield course we chose the latter, accepting the price in 

terms of difficulty and length, for the reward in insight. In either case, given the Boltzmann 

factor, a large number of interesting applications become immediately accessible. 

Eighth, simplicity and economy are essential but difficult features to achieve. Every simplification 

introduces detailed difficulties, often rather subtle ones which may remain hidden for a long 

time. The Nuffield approach raises as many as any other. The really hard thing is to carve out an 

economical approach which is coherent, taking in what one wants to include, and leaving out as 

much else as possible. Often this requires a rather careful analysis of just what lies behind a superficially 

simple argument. 

Lastly, most approaches depend critically on how they solve the problem of having a statistical 

approach without doing too much statistics. Feynman finds a way of doing no statistics; PSSC 

finds a very simple case and builds everything on that; Gurney uses more statistics but invents a 

quick way of avoiding purely technical mathematical problems, similarly used by Bent and 

Nuffield physics. Reif uses computer simulation, as does Nuffield physics, to inspect the 

behaviours of systems as opposed to analyzing and calculating them. 

The whole paper has assumed that the decision to introduce thermodynamic ideas in a statistical, 

or at least microscopic, way is right. It is clear that the decision creates considerable difficulties, 

but they should be seen in the light of the problems students have in understanding an uninterpreted 

macroscopic approach. 

REFERENCES 

ALDER, B.J., WAINWRIGHT, T.E. 1959. Molecular Motions. Scientific American, October. 

ANGRIST, S.W.; HEPLER, L.G. 1967. Order and Chrzos. New York, Basic Books. 

BENT, H.A. 1965. The Second Law. New York, Oxford University Press. 

BLACK, P.J.; DAVIES, P.; OGBORN, J. 1972. A Quantum Shuffling Game for Teaching Statistical Mechanics. 

American Journal ofPhysics,Vol. 39,p. 1154. 

EHRENBURG, W. 1967. Maxwell’s Demon. Scientific American, November. 

FEYNMAN, R.P., et al. 1963. The Feynman Lectures on Physics. Vol. 1. Reading, Mass., Addison-Wesley. 

GRASSIE, A.D.C. 1968. Introducing the Boltzmann Distribution. In: Sources ofphysics Teaching, pt. 1. London, 

Taylor & Francis. 

GURNEY, R.W. 1949. Introduction to Statistical Mechanics. New York, McGraw-Hill. 

HAMMERSLEY, J.M.; HANDSCOMBE, D.C. 1964. Monte Carlo Methods. London, Methuen. 

HANDSCOMBE, D.C. 1962. The Monte Carlo Method in Quantum Statistical Mechanics. Proceedings of the 

Cambridge PhilosophicalSociety, Vol. 60, p. 115-22. 

MILLEN, D.J. 1969. Energetics and Statistics in Chemical Energetics and the Curriculum. Glasgow, Collins. 

NUFFIELD ADVANCED CHEMISTRY. 1970. Teacher’s Guide ZZ. London, Longman. 

NUFFIELD ADVANCED PHYSICAL SCIENCE. 1972. Teacher’s Guide I. London, Longman. 

NUFFIELD ADVANCED PHYSICAL SCIENCE. 1974. Teacher’s Guide ZZI, (options). London, Longman. 

174

Introductory st at ist ical physics 

NUFFIELD ADVANCED PHYSICS, Unit 9.1972. Change and Chance. London, Longman. 

NUFFJELD ADVANCED PHYSICS. 1972. 16 mm fim. Change and Chance: A Model of Thermal Equilibrium in 

a Solid. (Penguin XX1673). 

NUFFIELD ADVANCED PHYSICS 1972.8 mm film loops. Forwards or Backwards? (Penguin XX1668-70). 

OGBORN, J. 1974. How the Normal Distribution Got its Hump. Mathematics Teaching. 

OGBORN, J. 1976 a.The Second Law of Thermodynamics: A Teaching Problem and Opportunity. School Science 

Review, June. 

OGBORN, J. 1976 b. Dialogues Concerning Two Old Sciences. Physics Education, Vol. 11, No. 4, June. 

OGBORN, J.; HOPGOOD, F.R.A.; BLACK, P.J. 1971. Chance and Thermal Equlibrium in Computers in the Undergraduate 

Science Curriculum. Chicago. 

OPEN UNIVERSITY. Course S100. 1971. Science Foundation Course. Unit 5, The States ofMatter; units 11, 12, 

Chemical Reactions. Milton Keynes, Open University Press. 

OPEN UNIVERSITY. Course T100. 1972. Technology Foundation Course. Units 20, 21, Energy Conversion, 

Power and Society. Milton Keynes, Open University Press. 

OPEN UNIVERSITY. Course TS262. 1973. Solids, Liquids and Gases. Milton Keynes, Open University Press. 

POWLES, J. 1968. Particles and Their Interactions. London, Addison-Wesley. 

PHYSICAL SCIENCE STUDY COMMITTEE (PSSC). 1968. College Physics. Boston, Mass., Raytheon Education Co. 

PHYSICAL SCIENCE STUDY COMMITTEE (PSSC). 1968. Physics: Advanced Topics Supplement. Boston, Mass., 

D.C. Heath. 

REF, F. 1965. Statistical Physics; Berkeley Physics Course, Vol. 5. New York, McGraw-Hill. 

REYNOLDS, W.C. 1965. Thermodynamics. New York, McGraw-Hill. 

SHERWIN, C.W. 1961. Basic Concepts of Physics. New York, Holt, Rinehart, Winston. 

SPICE, J.E. 1968. Introducing the Boltzmann Distribution. In: Sources of Physics Teaching, pt. 1. London, 

Taylor & Francis. 

TABOR, D. 1969. Gases, Liquids and Solids. Harmondsworth, United Kingdom, Penguin. 

175

Part I11 

The Place of Optics in Physics Teaching

Children’s ideas about light 

Childrens’ ideas about light 

E. GUESNE. 

We shall discuss the ideas held by children of 13 and 14, as revealed during a series of interviews 

conducted with children of that age on the subject of light. 

This survey was carried out as part of an effort to develop the teaching of optics to that agegroup 

[ I, 21. This was to provide a first introduction to the subject. The children interviewed 

had received no systematic teaching on the subject of light. They did, however, have certain ideas 

associated with the word ‘light’ and particular ways of interpreting the related phenomena. Those 

ideas and interpretations, drawn from their everyday life and from the notions received from 

those around them and from children’s newspapers, do not always correspond to the physicist’s 

way of looking at things. It is important to find out what these are if we are to be able to define 

objectives suited to the age-group under consideration. In this particular instance, we were also 

able to obtain guidance regarding the experiments that might or might not help children to 

understand the desired concepts. We shall be giving examples of these. 

We questioned some thirty children by means of standardized individual interviews. Each interview 

lasted about an hour. The questions were of two types: (i) very general questions that 

enabled us to find out what properties and what range of their own personal experience are 

spontaneously linked by children to the word ‘light’:‘What do you understand by light?’ ‘What 

does light do?’ ‘Where is there light?’; (ii) questions bearing on experimental situations set before 

the child, where he was asked either to anticipate or to interpret an observation: for instance, 

having placed before the child a small bulb (not connected), an upright stick and a screen (figure I), 

we asked him to predict, before lighting the bulb, the exact size and position of the shadow of 

the stick, by drawing it on the screen, and to explain what a shadow is. 

A similar approach was adopted by A. Tiberghien [3] with children of 10 and 1 1. Comparison 

of our findings revealed a distinct progression in children between these two age groups. We shall 

describe this progress. 

179


Figure 1. 

LIGHT AND SHADOW: IN WHICH IT BECOMES CLEAR THAT CHILDREN AND PHYSICISTS 

DO NOT ALWAYS HAVE THE SAME IDEAS ABOUT LIGHT 

Here are a few typical answers obtained regarding shadows: 

‘[A shadow] it’s a . . . it’s a reflection but . . . it’s a darker light’. [E5, 15 years.] 

‘[The interviewer asks if there is any light on the chairs in the room] . . . On some of them, there isn’t any, 

because they’re in shadow. . . .Under the tables . . . . . . . . (There’s shade) Because there are . . . tables which 

hide the light . . . . . . . . (A shadow) It’s the reflection of a . . . of a person or a thing . . . . You can’t really see 

the person . . . . You just see the shadow . . . . . . . . the light shines on the person . . . behind the person, reflects 

his shadow’. [Gl, 14 years, 4 months.] 

‘. . . The light, uh . . . sets off. And then it meets an object. . . . It lights it up, but behind, it can’t get through 

it . . . . So its black, then that makes the shadow’. [E6, 14 years, 10 months.] 

These three answers are not in the same class. The first two merely note the similarity of form 

between the object and its shadow (‘It’s the reflection . . .’). Only the last child is able to see the 

formation of shadow as the result of a process. He considers the light to be an entity in movement 

in space (it ‘sets off‘, ‘meets’, ‘gets through’ . . .). He is then able to interpret the shadow in terms 

of the obstacle presented by the object to the passage of light. The other two children reveal a 

different idea about light which does not enable them to go so far in their interpretation of 

shadows. We found that a number of other children gave evidence of the same idea in a variety 

of situations. 

These children then equate the light with its source or with its effects instead of regarding it 

(as physicists do) as a separate entity, situated in space. 

Light is confused with its effects when the first child (E5) says that the shadow (effect) is a 

‘darker light’ or when a child sees light only in the places where bright spots are produced on a 

wall by the light of the sun or the light reflected by a mirror. 

Conversely, light is equated with its source when, for instance, it is seen as being located 

exclusively in the light-bulbs: ‘(There is light) in the bulbs, it’s the bulbs which light up’. [F8, 

14 years, 3 months.] The interpretation of shadows put forward by the second child (‘tables 

hide the light’) can be placed in this category (light = source). 

180 

Light is also sometimes equated with a state: ‘Light is brightness. . . it depends on the weather,


some days it’s brighter than others’. [Lionel, 13 years, 7 months.] This way of identifying light 

with a state is similar to identifying it with its effects, but not quite the same. 

We have thus seen, in connection with the interpretation of shadows, that two different conceptions 

of light emerge: (i) light equated with its source, with its effects or with a state; (ii) light 

recognized as a separate entity, situated in space between its source and the effects that it produces. 

These two different conceptions reappeared in a variety of situations, and it transpired that the 

same child can draw on either one of these conceptions, according to the situation, and sometimes 

even when explaining the same phenomenon. Thus Lionel first explains the formation of a 

shadow on the table using terms that suggest the idea of a movement of light in space: ‘When 

you take away the paper, the light comes back on the table. If you put it back, the light won’t 

be able topass through the paper and the table is bound to be in shadow.’ And, after this explanation, 

he immediately adds an interpretation of the type ‘light = effect’, ‘light = state’: ‘[The light] 

is hidden under the shadow. It becomes the shadow of the paper. ’ It is hence impossible to judge 

a child on the basis of a single answer. To know how he stands in relation to the concept of ‘light 

as an entity in space’, it is necessary to determine the range of situations in which the child uses 

this concept by setting him face to face with a variety of examples. 

A g k eat deal of variety is then seen in the answers given by children aged 13 and 14. The two 

extreme levels of interpretation are represented as are all the intermediate levels in which the 

child uses, to a varying degree and in a varying number of different situations, dynamic terms 

(set off, meet, go through, rebound, etc.) that suggest a movement of light in space, and in which 

he loqates the light, more or less invariably, ‘everywhere in space’ rather than ‘in the bulbs’ or 

‘on the ceiling, in the chandelier’. However, if all the children of 13 and 14 are compared with 

those of 10 and 1 1 [3], it is seen that the older children make greater use of dynamic terms. At 

the ages of 13 and 14, very few fail to use such a term in some situation. Correlatively, a majority 

of them has recourse to the concept of ‘light as an entity in space’ to interpret the formation 

of shadows, in contrast with children of 10 and 11. Overall, then, there is a distinct evolution 

in children of 13 and 14 in relation to younger children: from identifying light with its source 

or with its effects, children go on to recognize light as a separate entity, in movement in space. 

The fact that they have understood the concept of ‘light as an entity in space’ does not mean, 

however, that their ideas about light are altogether satisfactory from the physicist’s point of 

view. The limits of this concept in the minds of children of 13 and 14 wil be seen subsequently. 

THE PROPAGATION OF LIGHT 

We have just seen that most children of 13 and 14 use, to a varying degree, dynamic terms in 

connection with light (set off, go through, rebound, etc.). These terms suggest the idea of a movement 

of light in space. However, the children never refer explicitly to a movement of light in 

space, except in the case of very great distances, concerning which some say to us, for instance: 

‘Well I know, for instance, that if all at once the sun . . . went out, well, you know, if the sun’s flames stopped 

burning, you could say . . . well that . . . you’d have some . . . some light for quite a time, because the sun would 

already have sent out some . . . some rays . . . and the rays, well, they, they wouldn’t go out . . . only the sun’s 

core would . . . so during this time . . . during the . . . p’raps four months, I don’t know how long it takes a ray 

to get to earth.. .it . . .it goes fast, okay, but it takes . . . takes time even so. . . . It can’t come just like that. . . .’ 

[F4, 13 years, 2 months.] 

This does not mean that they apply this concept of the time needed for light to be propagated in 

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the case of their immediate environment where this time interval is not perceptible. The child 

who spoke the above words concerning the sun continued by expanding on his views as follows: 

‘(For the lamp) . . . it’s not the light which takes time there, it’s the electricity which is coming to the lamp . . . 

so as soon as the electricity gets there . . . well, the light . . . anyway the lamp reacts and starts . . . shining.’ 

We also tested the concept of the rectilinear path of light. This concept can be wholly dissociated 

from the notion of propagation time. Children are in fact able to conceive of light in terms 

of rectilinear rays without realizing that there is any movement of light along those straight lines. 

About one-third of the children drew correctly on the concept of the rectilinear path of light 

in order to predict the size of the shadow cast by the stick (figure 1) or to predict the position 

of the light spot on a screen, placed behind a piece of cardboard with a hole in it higher than 

the bulb (figure 2). This finding was confirmed by a written questionnaire, submitted to 250 

13 and 14 year olds. 

Figure 2. 

A number of children also had the idea of a straight line, but envisaged only a horizontal 

plane. This being so, they predicted that the screen in figure 2 would not receive any light as the 

hole was not ‘opposite’ the lamp (i.e. on the same horizontal line). In all, the idea of a straight 

line is thus seen to be present in the minds of half of the children of this age. 

LIGHT AND ITS INTERACTIONS WITH MATTER: LENSES, MIRRORS AND OTHER 

OBJECTS 

The reflection of light by objects 

Turning our attention to the reflection of light by objects, we set before the children a sheet of 

white paper, then a mirror, placed opposite an electric torch (figure 3), and asked them: ‘When I 

turn on the torch, what does the light do?’ 

Most of the children thought that the light, sent out by the torch, remained on the paper, 

while the mirror sent it back: 

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Figure 3. 

‘It [the light] bounces off the mirror [gesture of the child going from the torch to the mirror, then towards 

herself]. . . . When the light falls on the paper, that makes a screen. . . . It stays there . . . whereas the mirror 

sends the light back.’ [El 1,14 years.] 

This idea derives directly from what is perceived: with the mirror, it is possible to light up 

something else or to dazzle someone, whereas, in the case of the sheet of paper, the most apparent 

effect is seen to be on the paper. A few children thought that the light must disappear rather than 

remain, on the paper: 

‘It surely doesn’t remain. If it did, you’d only have to turn it off for it to stay there. So it can’t stay there. . . . It 

must light up and then disappear . . . since it can’t stay there.’ [E17, 13 years.] 

In the previous interpretations, light was seen as an entity in movement in space (as far as the 

paper). We were also presented with interpretations in which the light was equated with its source 

or with its effects, as with children of 10 and 1 1 [ 31 , but in a smaller proportion: in this case, the 

child is unable to reason in terms of a path of light; he merely notes the presence of the light spot 

on the sheet of paper (‘What does the light do?’ ‘It makes, for example, a sun.’ E4, 15 years, 2 

months); again, with the mirror, he merely describes what he sees (‘You see the light. .. in the 

mirror. . .. [You see] the lamp.’ E4). It is important not to overlook the case of such children. 

For them, a first step wil be to recognize the existence of the entity ‘light in space’. 

However, the dominant fact to emerge is that practically no child suspects that ordinary 

objects send back the light. Now this concept is of fundamental importance for the entire field 

of optics. It is not possible to understand the formation of images of any object whatsoever 

(that is not in itself luminous), as in photography for instance, unless this concept is first of all 

grasped. We shall see, similarly, that it is decisive for an understanding of how we see. Hence 

it is a basic aim in the teaching of optics at that age to get across this concept. Use can be made 

of the example of the mirror, already recognized by most children as reflecting light. The children 

refer to the fact that with a mirror it is possible to light up another object or to dazzle someone. 

With a sheet of light-coloured paper similar effects can be produced. At noon, in the middle of 

summer, a piece of white paper lit up by sunlight has a dazzling effect; in a dark room, the fact 

that an object (of a light colour) is lit up by the light reflected on a sheet of light-coloured paper 

is clearly perceptible. We see here how, once we know what ideas children hold, we are in a good 

position to decide relevant objectives for the age-group considered and to know how to achieve 

them. 

The role of the magnifying glass 

Children know that they can set things on fire with a magnifying glass on a sunny day; many have 

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already done so. We wanted to know how they interpreted this. 

E17 (13 years): ‘. . . It makes it bigger. . . . So it ought to make the light bigger. And as the light heats up anyway. 

. . . Because if you put it there, at the end of an hour, it’s going to bum. . . . But as the lens makes it 

bigger. . . . . . . . there’s going to be lots of light, I think.’ 

E15 (13 years, 2 months): ‘It concentrates the light.’ 

I (interviewer): ‘Yes. Yes, you can make a drawing.’ 

E15: ‘As the light is more or less hot. ...’ 

I: ‘Yes. Here you are, do a drawing. Show me where the sun is, where you put the paper and the lens.’ 

E15: ‘Well, here for instance is the sun. [I: Yes.] The paper is there. [I: Yes.] It spreads out all around. It goes 

like that and therefore it’s concentrated.’ 

Figure 4. 

I: ‘Is there more light behind the lens than in front?’ 

E15: ‘No, but it’s more concentrated in one spot.’ 

Children of 13 and 14 are divided, in comparable numbers, between these two answers: ‘The 

magnifying glass makes the light bigger’ or ‘The magnifying glass concentrates the light’. Among 

the children who think that the magnifying glass makes the light ‘bigger’, some, like the first child 

[E17], think that there is more light behind the magnifying glass; others think that there are ‘just 

as many rays, but they’re . . . they’re stronger’ [E 10,14 years, 7 months] . Those children who have 

the idea that the magnifying glass concentrates the light are not necessarily as close to the view 

held by the physicist as is the child EIS. Thus E18 (14 years) produced the following drawing 

(figure 5) to show how the magnifying glass concentrates the light. However, all consider that the 

total amount of light passing through the magnifying glass is conserved, in contrast with those 

children who think that the magnifying glass makes the light ‘bigger’, i.e. increases or intensifies it. 

We encountered other cases where the idea that the quantity of light is conserved was not 

expressed by the children. Thus, for some, light is subject to change with distance: 

‘. . . At one point it stops because it’s too far. . . . At one point it can’t go on . . .you can’t see it any more. . . . 

I think that it can’t go through air any more, or else it . . . it’s because it can’t go through the air any more, it’s 

lost its . . . its density’ [E17, 13 years] . 

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Figure 5. 

We saw that the same child thought that there was more light behind the magnifying glass because 

the lens ‘makes the light bigger’. In his view light can get lost, disappear or, on the contrary, 

intensify. It may be observed again here that the ideas formed by children are connected with 

what they perceive. El 7 associated the idea that the light stops with the fact that it can no longer 

be seen. Thus, for the children, the presence of light is linked to the manifestation of a perceptible 

effect. For them, the light is powerful; when it loses its strength, it ceases to be. 

LIGHT AND ELECTRIC LIGHT 

Children consider electric light and sunlight to belong to two clearly distinct categories: 

‘There’s sunlight which provides us with daylight . . . and then there’s the light which is made, electric light to 

illuminate us. . . .’ [G2, 13 years, 11 months.] 

In some cases even, electric light alone is spontaneously associated by the child with the word 

‘light’. Thus, when we asked her, ‘What do you understand by light?’, F8 (14 years, 3 months) 

replied 1 

‘It’s the light bulbs which light up . . . and that . . . and the light is made by dams . . . or some . . . something like 

that . . . mainly dams. . . . Well,the water turns in the turbines and it gives light. . . . It’s the (electric) current 

which gives the light.’ 

When we asked her, ‘Where is there light?’ she went on as follows: 

‘There’s light everywhere. . . . Well,yes, er . . . in the streets, in . . . there, in the houses . . . in cars too. . . . Everywhere. 

[I: Andhere,in thisroom,is there any light?] Not at the moment . . .you have to switch on, there. . . . [I: There’s 

no light at the moment?] Yes, daylight . . . but not the, er . . . electric light. [I: It’s not the same?] No, because 

there’s sunlight, and then there’s lights, like that. [I: And the sunlight, is it light?] Well,yes . . . because you can 

make light by . . . the sun . . . yes, with the sun, I don’t know how really but certainly . . . well,I don’t know, 

the sun should . . . yes certainly. 

[There is light] in houses . . . outside . . . in cars . . . well pretty well everywhere . . . everywhere where there are 

men, where you have to light up . . . not particularly for men, also in factories, well everywhere, for . . . so that 

. . . so that you can see. 

[Here] There’s light, but it’s not turned on. . . . Well . . . you’d have to switch on there, at the switch . . . and 

there’ll be light.’ 

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LIGHT AND DAYLIGHT 

Children see a causal relationship between the sun and daylight, but this relationship remains 

fairly vague, as in the case of G2 who told us earlier: ‘There’s sunlight which provides us with 

daylight . . .’. 

They are able to interpret the alternation of day and night by considering the fact that the 

side of the earth that faces the sun is lit up: 

‘Twelve hours a . . . day, the light is . . . it’s on us . . . on France . . . and . . . for twelve hours, it’s . . . it’s no 

longer on France, I don’t know what country it’s on. . . . It’s because the earth is . . . is round, it’s spherical, so 

when . . . when there’s one side of the earth which is facing the sun, the rays go . . . go where they can, they 

won’t go round the earth to light up the other side, behind the earth . . . so they . . . they light up the side which 

is . . . facing the sun . . . so . . . the other side is not lit up, it’s night-time for the other part.’ [F4, 13 years, 2 

months.] 

However, they were altogether at a loss to interpret the light that is all around us when it is 

daytime. The understanding of daylight requires some appreciation of the scattering of sunlight 

in the atmosphere. When we consider the fact that the children do not even realize that light 

is reflected by solid objects, it is easy to appreciate that they do not understand the result of an 

interaction between the air and the light. And it is a fact that their descriptions of daylight are 

somewhat confused when reference is being made not to the opposition between daytime and 

night-time but to the light that is all around us: 

‘There’s light everywhere (in the room) . . . well, it’s not light, it’s something to enable us to see, I’d say. . . . 

It’s not really light. . . . When you look at a candle or a lamp, you say, well, that, that makes light whereas there, 

that’s not light, you can’t say, well,there, that, that makes light, you’re in a room, there’s light there, but it’s . . . 

it’s . . . the room doesn’t make the light.’ [F7, 13 years, 9 months.] 

‘[It’s daytime] because there’s sunshine. ... Well sometimes, there’s not always sunshine, it rains, but ... nevertheless 

its daytime. ... I don’t know why that is . . . [When there is sunshine, that is to say] it’s good weather 

... it lights up more ... because when it rains or when it snows, well ... it’s dark ... because there are clouds 

.. . grey clouds ... so it covers the sun ... the ...not the sun, the sky ...well it ... makes it ...it makes the 

sky dark. .. the sky, yes ...’[F8,14 

years, 3 months.] 

F7 was put out because she could not manage to identify the source of the light. How can it 

be understood that a room that does not receive direct sunlight, whose windows are exposed 

to the north for instance, is lit up? F8, for her part, could not understand how it could be daytime 

when there was no sun. What was missing in her case was the idea of ‘light as an entity in 

movement in space’ which would in itself have enabled her to interpret the daylight as the light 

that comes to us from the sun, more or less intense according to the layer of cloud it has to pass 

through. This is a first step towards understanding situations in which the sunlight cannot come 

to us in a straight line but reaches us after being diffused in every direction by the atmosphere. 

LIGHT AND VISION 

Children make a very strong association between light and the fact of being able to see. The 

questions ‘What do you understand by light?’ and ‘What does light do?’, asked at the beginning 

of the interview, brought out two dominant ideas: light illuminates; and light makes it possible 

to see. 

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We wanted to know more specifically how they explained the phenomenon of sight and how 

they thought that light contributed to it. We accordingly asked them two questions: one concerned 

the visual perception of a primary source, a lighted stick of incense; the other the visual 

perception of an ordinary object, a multicoloured cardboard box. The two objects perhaps 

represented different situations for the children. 

Is light thought to be received by the eye? 

We first presented the incense stick, asking the children whether he could see its (glowing) tip 

so that he would be fully aware of seeing it. Then we asked him: ‘Does it send out light?’ in 

order to‘ find out whether, for him, the fact of his seeing it was connected with the idea that the 

eye receives light. 

Most of the children thought that it did not send out ‘any light at all’ [E2, 14 years, 9 months] 

or ‘not very far’, and in any case not as far as them, at a distance of about 1 metre from the stick. 

El 1 [ 14 years] :‘It doesn’t send out any, it stays where it is.’ 

E8 [14 years, 10 months] : ‘It sends out very little. ... It’s chiefly the colour that gives .. . it’s chiefly the 

colour of. .. of the stick that gives the effect of light. ...’ 

I: ‘Does it send out light all the way to you?’ 

E8: ‘I don’t think so. No, it stays around the stick. It doesn’t go any further.’ 

I: ‘Is this end sending out light?’ 

E17 [ 13 years] :‘Yes ... But much less than that [he indicates the torch which had just been used] .’ 

I: ‘Much less strong. ... How far does it go?’ 

E17: ‘I don’t know. ... Well,much less far, only a little. [He holds the incense stick close to a sheet of paper.] 

Oh, even like that, it’s not sending out any light. ... You can see it, because it’s red, otherwise. ...’ 

Here again, E 17 connects the presence of light with the manifestation of an effect of sufficient 

intensity for it to be perceptible, namely, the lighting up of the sheet of paper. However, the fact 

of seeing an object is not accompanied by any violent physical sensation - one is seldom dazzled. 

Recognizing the light only when it produces a highly perceptible effect, the children do not think 

that the eye can receive light. Light is needed for an object to be seen, but the light does not 

necessarily go as far as the eye. This was made explict by El 4 [ 13 years, 4 months] : 

I: ‘Is it sending out light?’ 

E14: ‘Yes.’ 

I: ‘Yes. Why?’ 

E14: ‘Because you can see it in the dark. . .. You can see it in the dark, so it gives out light, otherwise you 

couldn’t see it. ... Unless there’s another light. ...’ 

I: ‘Where does it send out light to?’ 

E14: ‘There[he indicates a point a few centimetres from the stick] .’ 

............................................................................ 

I: ‘When you see, does your eye receive light? Is there any light which goes in your eye?’ 

E14: ‘Not necessarily.’ 

I: ‘Not necessarily, no ...’ 

E14: ‘No, because with the incense stick, for instance, if I had binoculars, it could be one kilometre away, and I 

would see it just the same.’ 

Only a few children answered the question, ‘Does it send out light all the way to you?’ with 

the reply: ‘Yes . . . otherwise I wouldn’t see it’ [E6, 14 years, 10 months]. Such answers remain 

very vague. One or two, however, were more explict: 

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‘My idea is that the moment you see something, if it’s in the dark, it must be sending out light. . . . If I see something 

in complete darkness, and I see that thing, like that [he points to the lighted incense stick] or a lamp, I 

think it must be sending out light. If I see it a hundred metres away, it must be sending out light to a hundred 

metres. If I see it at a hundred and fifty metres, it’s sending out light to a hundred and fifty metres . . . . . . . . at 

least provided that it’s in complete darkness. Because if I see a cupboard or my coat because there’s light, I 

see it. But if in complete darkness I see something . . . and I can’t see anything else, well I think it must be sending 

out light. Because I can see it’ [E19,12 years, 5 months]. 

E 19 clearly distinguishes here between the case of glowing objects and that of ordinary objects. 

Rare as it is for it to be recognized that light is received by the eye in the case of an object such 

as the incense stick, it is even rarer in the case of ordinary objects. One child alone gave the same 

answer concerning the cardboard box as he had given concerning the glowing incense stick, thus 

giving proof of an interpretation that was satisfactory from the physicist’s point of view: 

‘. . . if I see the object . . . it must be because it gives me a bit of light. So . . . I can see it. . . .It [the light] gets to 

my eye . . . and then my eye it . . . it records. And it makes it possible, er . . . in my brain to form an image of 

the object’ [E18, 14 years]. 

object 

brain 

eye 

Figure 6. 

Another viewpoint 

Child E6, who was one of those who considered that the eye received light in the case of the 

glowing stick, said to us in respect of the cardboard box, contrasting it with the previous case: 

‘Here my eyes can go right up to the box. . . . It’s my sight. . . . If it [the box] was fifteen kilometres away, I 

couldn’t see it, because . . . my sight isn’t strong enough. . . . Because a box doesn’t move, it hasn’t any energy. 

A lamp, for instance, which moves, the light gets there. . . . The box, is something that isn’t alive.’ 

What we have here is an interpretation of the phenomenon of vision in which the eye is thought 

not to receive light but, on the contrary, to be an active agent. Likewise, E 12 [ 13 years, 8 months] 

said to us: 

‘It’s pretty much like the light, because it comes out. . . . The eye sees like this . . . it comes out like this [he 

draws lines going forwards or upwards from the eye according to the direction in which the eye is looking]. . . . 

The eyes haven’t got any light of their own, so they have to have a light that lights up when you want to see.’ 

In everyday language, which serves as a source or a reflection of commonly held views, the 

same idea is expressed. The eye is assigned an active role, whereas the object ‘looked at’ has but 

a passive role: the eyes examine, search out, scrutinize, and so on. In romantic literature eyes 

flash, looks can kill. . . . And it is true that when one looks at an object, one has the impression 

of being more an active subject than a passive receiver. Any comprehensive theory of vision 

includes physical, physiological and psychological aspects. This sense of an active subject, 

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connected with the psychological aspects, is reflected in the idea subscribed to by Plato and the 

Pythagorean school that there exists a ’visual fire’.For Plato, ‘. . . the Gods caused the pure fire 

within us, which is akin to that of day, to flow through the eyes in a smooth and dense stream. ... 

So whenever the stream of vision is surrounded by midday light, it flows out like unto like, and 

coalescing therewith it forms one kindred substance along the path of the eyes’ vision. ... And 

this substance distributes the motions of every object it touches, or whereby it is touched, 

throughout all the body even unto the Soul, and brings about that sensation which we now term 

“seeing” ’ (Plato’s Dialogues: the Tirnaeus). The Pythagoreans considered that sight was due / 

exclusively to an invisible fire coming out of the eyes. As this fire (or, according to Euclid, this 

cluster of rays) touched objects, it made their forms and colours known. At the end of the fourth 

century, Theon of Alexandria thought that the rays of light sent out by the eyes must be at some 

distance from one another for ‘a thing cannot be entirely seen at a single glance: sometimes, 

searching for a small object on the ground, a needle for instance, one does not see it although it 

is concealed by no obstacle; but when one has directed one’s gaze to where it actually is, it is 

seen without difficulty; likewise, one does not see simultaneously all the letters on a written 

page’ [41. 

For children, the movement that goes from the eyes to the object remains abstract. It is thus 

clearly differentiated from the ‘visual fire’ of early theories, from the ‘fluid’ emitted by the eyes 

of witches in fairytales or from the red rays that are beamed from Superman’s eyes. Only the 

idea that the subject is at the origin of a process, instead of being at the receiving end, is common 

to these various ways of portraying sight. The idea is an important one, substantively speaking. 

We found evidence of it, however, in only very few children. Consequently, it should not be 

given more importance than it actually has from the quantitative standpoint, despite the temptation 

that always exists to find historical parallels. 

The dominant viewpoint 

Most of the children did not point to any form of link between the eye and the object. 

I 

I: ‘How is it that you see this box at this particular moment?’ 

E9: [ 14 years, 3 months] :‘Because it’s in front of my eyes, here, I see it.’ 

I: ‘... Yes. ... How is it that you see it?’ 

E9: ‘I can see it on account of daylight, because in the dark I wouldn’t see it ... because in the dark there’s no 

light ... there’s no daylight. ... The eyes need daylight, need light, in order to see clearly.’ 

E2 [ 14 years, 9 months] :‘It’s thanks to the light that we see the box. ... [It’s role is] to light up objects so that 

we see them.’ 

Some drew a diagram of the inverted image formed on the retina. This was but the memory 

of something learned at school, reproduced without any sort of explanation. 

What do the two intersecting lines represent? The child who had drawn them [E17, 13 years] 

did not know. All recognized that nothing could be seen without light. But most of them referred 

to light only in so far as it lit up the object or as the ambient medium (daylight) surrounding 

object and observer without distinguishing any specific linking function. The eye ‘sees’ without 

anything connecting it to the object. 

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Figure 7. 

Conclusion 

The children’s ideas about the visual perception of any object can be summed up by the following 

diagrams (figures 8 to 11): 

obiect obiect obiect 

Figure 8. 

Figure 9. Figure 10. 

Figure 11. 

Figure 8 shows the ‘ambient light’: no interconnection is seen between the eye, the light and the 

object. In the case of figure 9, once again the need for a link between the eye and the object is 

not recognized by the child, but the light has a more precise role: it lights up the object. These 

two diagrams are equally representative of the ideas formed by the very large majority of the 

children. For, as we saw, very few children imagined ‘sight’ to be a movement, represented 

diagramatically in figure 10, going from the eye to the object, and the explanation given by 

physicists, represented in figure 11, was very seldom put forward by the children, especially 

in the case of objects that were not luminous in themselves. This is connected with the fact that 

they do not suspect that objects reflect light. 

These ideas about vision are important on their own account: the explanation given by the 

physicist, who considers the eye to be light-receptive, is not a part of established knowledge. 

One of the aims of education must be to make that explanation known. These ideas about vision 

are also important with regard to the validity of certain standard experiments carried out in 

physics classes. In the field of optics, for instance, many courses begin by establishing that light 

is propagated in a straight line, and this is done by carrying out the following experiment: it is 

demonstrated to the pupil that he cannot see a candle flame through a series of cardboard sheets 

with holes, unless the holes are in a straight line [5]. To apply this observation, the path of a 

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‘light ray’ is marked out by means of pins stuck in a sheet of paper in such a way that the one 

closest to the eye exactly masks the following ones [6]. The significance of these experiments 

for the children is not that which is assigned to them by their authors. They cannot be interpreted 

in terms of a path of light going from the object to the eye when the visual perception of the 

flame or of the pins is not connected with the fact that light is received by the eye. In the process 

of teaching, one must arrive at a more satisfactory model of vision; one should not take such a 

model as a starting point, in the mistaken belief that the children have mastered it already. 

CONCLUSION: THE IDEAS THAT ARE HELD ABOUT LIGHT 

In the foregoing paragraphs, two quite different ideas about light were seen to emerge. On the 

one hand, light was equated with its source or with its effects; on the other, light was seen, as 

by the physicist, to be a separate entity, situated in space. In the first case, the children have no 

means of interpreting related phenomena: they can only note the similarity in form between 

an object and its shadow or the presence of an image of the source in the mirror. The second 

view represents a definite step forward: the children can then interpret shadows and raise the 

question of the reflection of light by objects, a question which has no meaning so long as the 

concept of light as an entity in space, differentiated from its source and from its effects, has not 

been mastered. However, this is but a first step towards f0rming.a picture consistent with the 

physicist’s model. We saw the limits of this view in the minds of 13 and 14 year old children: 

(i) the movement of light is not clearly recognized: the children often speak of light as an entity 

in movement (it sets off, goes through, rebounds, etc.) but they recoil from explicitly envisaging 

the movement of light except, for some, in the case of great distances; (ii) light exists for those 

children only when it is intense, and sufficiently intense to produce perceptible effects; they are 

thus led to think that, in contrast with the mirror, the sheet of paper does not reflect light and 

that their eyes do not necessarily receive light when they look at an object; and (iii) the children 

do not think that light is necessarily conserved; for many of them it may vanish (irrespective of 

any interaction with matter when it is no longer sufficiently intense to produce perceptible 

effects) or, on the contrary, be intensified (when it passes through the magnifying glass). 

The children sometimes conceive of light as an entity in space, but they always do so in 

material terms. Thus El7 [13 years] said to us, in connection with the light projected by the 

lamp on to the mirror: ‘The light. . . it’s solid . . . so it should come back. . . .’ When it is a piece 

of cottonwool that is lit up by the lamp, he explains that the light wil not be sent back by it 

‘because it’s not hard’. Such a ‘material’ view may help the children to interpret certain phenomena, 

such as the interaction of light with a mirror; but in other cases it prevents him from 

understanding, as in the case of El 2 with the magnifying glass: 

‘My idea is that the rays don’t go through. It’s the light that goes through. What I mean is that it doesn’t go 

through, but it ...,how can I put it, it. ... [I: ... the rays aren’t the same thing as the light?] Yes they are, 

but. .. . The rays and the light are the same thing. They don’t go straight through, there are no little holes 

for them to go through’. 

In relation to the identification of light with its source and with its effects, the idea that light 

is an entity in space, possessing properties to which the physicist would be more or less ready to 

give his assent, clearly represents an advance and not merely a better alternative idea. Inde-d 

children seem to subscribe successively first to one and then to the other; we saw that at 10 

and 11, most children hold the first idea, whereas at 13 and 14, the second idea is dominant. 

While, however, the concept of light as an entity in space is drawn upon by most children 

191


aged 13 and 14, not all children of that age have reached the same stage in their development. 

Some of them still identify light completely with its source or with its effects; many of them 

refer to the concept of light as an entity in space only in a limited number of situations. In 

addition, they often assign to that entity properties to which the physicist would not give his 

assent. We must discover the ideas held by children if we want to have a greater chance of helping 

them to progress. 

REFERENCES 

1. 

2. 

3. 

4. 

5. 

6. 

GUESNE, E.; BARBOUX, M.ModuZe photographie. Paris, LIRESPT, 1977. 

Sciences physiques en clusse de 4e. Paris, Hachette, 1979. (Collection Libres Parcours.) [Pupil’s book and 

teacher’s book.] 

TIBERGHIEN, A. et al., Conception de la lumi&re chez l’enfant de 10-12 ans. Revue francaise de pldagogie, 

NO. 50,1980, p. 24-41. 

RONCHI, V. Histoire de la lumiere. Paris, A. Colin, 1956. 

Sciences physiques en classe de 4e. Paris, Magnard, 1979. 

Sciences physiques en classe de 4e. Paris, F. Nathan, 1979. 

192

Colour 

Colour 

R.D. EDGE. 

Colour, like pitch in music, is a perceptual quantity - what we see, light from objects, is observed 

by the human eye and interpreted by the brain. Physics represents only a part of this, but it is the 

part most easily dealt with. Nevertheless, teaching art students and other non-physicists the 

physical basis of colour and its relationship to the appearance of pigments, colour film and colour 

television presents no easy task - an artist perceives colour in quite a different way from a dye 

chemist or a physicist. Because colour overlaps the provinces of physics, psychology and engineering, 

the terminology used is mixed and confusing. Emphasis wil be laid on these differences to 

try to avoid this problem. 

LIGHT 

Thomas Young first demonstrated light to be a wave phenomenon in 1801 by showing that the 

troughs and crests of two overlapping beams of light can interfere to produce visible dark and 

bright bands. In 1864 Maxwell showed light to be a form of electromagnetic radiation. Long 

before Newton’s Opticks [ 11 , it was known that white light could be spread into a spectrum of 

colours by a glass prism. The actual range of wavelengths which can be seen is small - from 360 

to 740 nm (1 nanometre = lo-’ m), less than a factor of two, an octave. Although we shall 

describe light as a wave in our discussions of colour and in its path from the source to the eye, 

modern investigations show its production and detection can often be more easily described by 

particle behaviour - the ‘photon> of light. Once we have split the light emitted by, or reflected 

from, an object into its component wavelengths, as by a prism, and measured how much of each 

there is, thus obtaining the intensity spectrum, we have virtually completed the physical specification 

of that light - there is little else to discuss. (We are not interested in polarization - the 

vibration direction of the light.) However, the colour which we perceive wil also depend on the 

surroundings of our object, how bright the illumination is and other factors. 

Light is energy, and as such may be converted into other forms of energy - such as heat (as 

we notice, sitting in the sun) or electrical energy, as by a photocell. We are interested in the 

illumination of objects and wish to measure the flow of the light energy onto objects we observe. 

The radiance, or flow of light energy per unit area (sometimes called the flux) is measured in 

physical units of watts per square metre, the watt being a joule per second. 

193


TRICOLOUR VISION 

‘For the Rays (of light) to speak properly are not coloured. In them there is nothing else than a 

certain Power and Disposition to stir up a sensation of this or that Colour’. [Newton, 1 .] 

Our hearing process can pick out one frequency mixed in with many others. Not so our eyes. 

Whereas a given intensity spectrum of a light, surrounded by the same background, wil always 

produce the same visual sensation, that sensation may also be elicited by many different spectra 

- for example, the sensation of turquoise may be produced by a band of wavelengths at 490 nm, 

or by a rather broad mixture of blue and green light. 

In 1806 Young suggested that the sensation of any colour could be produced by a mixture of 

only three ‘primary colours’. However, Young was a rather unpopular figure at the time, and it 

was not until later when the German physicist Helmholtz championed the theory that it was 

accepted. In the 1860s, Maxwell developed his colour triangle to represent the proportions of 

such colours necessary, as shown in figure 1. The three primary colours, from which the others 

were to be derived, were placed at the apexes of the triangle, and a point here represented 100 

per cent of these colours. Any other colour could be matched by a combination of these three, 

in different proportions, so that point A in figure 1 is a turquoise which can be matched by 40 

per cent blue, 40 per cent green and 20 per cent red. 

It should be emphasized that the matches were made by eye - and hence depended entirely 

on the observer’s vision - and that it was the illuminants that were added - i.e. the illumination 

produced by red, green and blue lights matched the illumination of the test lamp. In practice, 

the lights were compared by shining them onto the same sheet of white material. As discussed 

later, the scientific justification for the three colour theory was only confirmed quite recently. 

Maxwell’s triangle gave only crude-quantitative measurements, so in 193 1, the Conseil International 

d’Eclairage (CIE) devised a truly quantitative method for specifying the proportions 

green 

blue magenta red 

Figure 1. Maxwell’s colour triangle. 

194

Colour 

of three primary colours necessary to match any other colour. The CIE diagram is based on an 

experimental match of the spectral wavelengths with the sum of different quantities of three 

narrow wavelength bands, a red of 700 nm, a green of 546.1 nm and a blue of 435.8 nm. The 

cone cells of the retina which are the elements responding to the three bands of colour are 

sensitive over a broad range of wavelengths, so the choice of primaries is somewhat arbitrary, 

although there are obvious advantages to locating them at the two ends of the white light 

spectrum, and somewhere in the middle, where the cells are most sensitive. 

C 

a, 

a, 

L 

0 

U] 

a, 

U 

L 

3 

I 

test lamp 

m 

c 

Y 

[I) 

! 

observer 

Figure 2. Method for colour matching the light from a test lamp with three coloured lamps. 

Figure 2 shows diagrammatically how the colours were matched. Light from a test lamp 

(which could be a part of the white light spectrum, separated off by a slit) shines on a white 

screen, and is viewed by an observer. An adjacent part of the screen is illuminated by light from 

three lamps equipped to provide the narrow bands wavelengths given above. By adjusting the 

intensity of these lights, the observer makes their combined colour on the screen match that 

of the test lamp, thus matching the appearance of the light emitted from areas in the two parts 

of the screen. The screen must reflect uniformly, i.e. have the same reflection coefficient, 

throughout the spectrum. The luminance of the screen, defined in psycho-physical units as 

luminous flux per unit solid angle emitted per unit projected area (figure 3) is therefore the same 

for the two parts of the screen, i.e. they have the same relative luminance. Luminous flux, or 

luminance, is measured in lumens, where the lumen is the luminous flux per unit solid angle from 

a point source of unit luminous intensity. The unit of luminous intensity is the candela. It is 

the luminous intensity in the perpendicular direction of 1/60 cm2 of surface of a black body 

radiator (described under ‘white light sources’) at the freezing point of platinum (1774°C). (It 

is slightly larger than the international candle, which historically grew out of a real, stearine 

candle.) It is clear that these psycho-physical units are, to say the least, difficult to use, because 

they are dependent on the observer’s ability to match the appearance of different colours and 

observers differ. Much simpler is the watt per square metre, a unit of radiant flux which is purely 

physical. One difficulty with the psycho-physical system is that luminance is such a strong 

function of wavelength. In comparing the luminance of two sources, of, say, 400 and 500 nm, 

195


output IS 

luminance 

Figure 3. Definition of luminance. 

we do not compare their energy, but their effect on the eye. Thus, though both fluxes might have 

equal energy, in comparison the 500 nm flux would have a higher luminance, since the eye is 

more sensitive at 500 nm. Figure 4 shows the luminosity (luminosity is relative luminance) as a 

function of wavelength for the photopic (light adapted) and scotopic (dark adapted) eye. Clearly, 

the lumen, as we have defined it, is a function of the observer, so these curves - which are 

averages over many observers - have been taken as standards. Using our candela, the maximum 

value of absolute luminosity for scotopic vision (at 507 nm) is 1746 lumens per watt; it is 680 

lumens per watt for photopic vision. We shall rarely be interested in scotopic vision, which does 

not distinguish colour depending, as it does, on the rod cells of the retina as receptors. The 

amounts of the three primaries, measured as the luminance in lumens, which match the test 

colour are called the tristimulus values for that colour (Y) for red, (g) for green, (b) for blue. Note 

that the spectral distribution of the test lamp wil not be the same as that of the matching primaries. 

Two illuminants such as these which are perceived as having the same colour but have 

entirely different spectral distributions, are termed a ‘metameric’ pair. No three primary colours 

196

Colour 

400 500 600 700 

Wavelength/ nm 

Figure 4. Luminosity functions: the 1924 CIE photopic (light adapted) and the 1951 CIE scotopic (dark adapted) luminosity 

functions for young eyes. 

provide an exact match with all other test colours - for example, no combination of green and 

red can exactly match a bright yellow. To overcome this problem, light from one of the primaries 

can be added to the test colour, rather than mixed in with the other two primaries. In 

describing the test colour, this may be thought of as being subtracted from the other primaries. 

So, the bright yellow light would be matched by (Y) + (g)- (b) i.e. the yellow light plus (b) 

is matched by (Y) + (g). 

If we employ ‘negative’ amounts of light, as described above, any colour can be matched using 

only three primaries. 

The tristimulus values €or different spectral colours can now be obtained by employing these 

as the ‘test lamp’. The spectral colours are separated from a prismatic white light spectrum using 

a slit. If we arrange that the energy distribution through the spectrum remains constant as a 

function of wavelength (i.e. the same energy for each 10 nm, say), the tristimulus values are 

given in figure 5 as (TA), @A) and (6~). Note again that this is an average obtained by employing 

a large number of observers. Subsequent curves are derived from this experimental data. 

197


Wavelength /nrn 

IO 

Figure 5. Spectral tristimulus values. The amounts of the red (rh), green (gh) and blue (bh) primaries needed by a normal observer 

to match each of the colours of the equal energy spectrum (CIE 1931). 

So far, we have seen that the quantities for the red, blue and green primaries can be obtained 

experimentally to match a test la,mp. Now we have the spectral tristimulus values, we can calculate 

the quantities of the matching primaries from the spectrum produced by the test lamp. We 

split the spectrum into small wavelength divisions. The spectral energy at each division Eh is 

multiplied by the corresponding tristimulus value at that wavelength; this product is summed, 

and normalized as shown in figure 6. We should get the same value, using this calculation, as 

would an observer experimentally matching the three lamps to get (Y), (g) and (b). 

THE CIE CHROMATICITY DIAGRAM 

These three variables for different sources may be represented on a three dimensional plot, but 

this is obviously inconvenient. To ensure that the results have practical interest, CIE made three 

adjustments. The first involved the luminance of the source. CIE defined new co-ordinates 

(X, Y and 2) where 

X = 2.7869 (Y) + 0.38159 (g) + 18.801 (b) 

Y= (Y) + (s) + (b 1 

Z= 0.12307 (s) + 93.066 (b) 

We can now easily calculate X, Y and 2 from our measured values of (Y), (g) and (b). 

It wil be seen that, since the luminance of the source wil be the sum of the luminances of the 

three matching primaries, Y is the luminance of the source in the psycho-physical unit lumens. 

198

Colour 

a, 

; 

0 

E 

c 

\ 

L U 

Is) 

c 

- a, 

a, 

> 

5 

U 

0 

8 

0 

CO 

0 In 

E 

J 

L 

U 

a, 

a 

ffl 

a, 

U 

J 

0 

ffl 

d 

0 

U 

199


9- 

Figure 7. CIE chromaticity diagram. The wavelength of spectral colours is marked on the diagram in nm. 

Second, in plotting the results, the ratio of the CIE values for the test source are employed 

x=X/(X+Y+Z),y= Y/(X+Y+Z),z=Z/(X+ Y+Z) 

This eliminates the absolute brightness of the source, which is generally of lesser interest. Today 

the convention is normally to plot y against x in rectangular co-ordinates, the result being called 

the chromaticity diagram. The plot itself for the spectral colours, shown in figure 7, crudely 

resembles Maxwell’s colour triangle, with red and blue at the bottom corners, and green at the 

top. The spectral hues run around the edges of the curve, the wavelengths being in nanometres, 

and any possible colour can be represented by a point inside. 

This diagram incorporates the third adjustment. In order to eliminate negative values, the axes 

of the (r) (s) (b) plot were displaced. Then, in plotting the displaced x against the displaced y, all 

real colours are positive, although the axes are no longer directly related to the standard illuminants 

i.e. x = 0, y = 0, no longer means 100 per cent illumination by a blue of 435.8 nm it is 

instead, a fictitious illuminant not realizable in practice. Nevertheless, we can calculate a series 

of tristimulus values for this new system from those already measured, and the results, called 

?A, and ?A are shown in figure 8. If we now multiply the energy spectrum from our test lamp 

200

Colour 

200 

150 

(I] 

U C 

; 1 0 0 

E 

m 

a, 

2 

U 

- m 

a, 

[I 

50 

0 

400 500 600 700 

Wavelength / n m 

Tristimulus Values of Equal Energy Spectrum 

Figure 8. Spectral tristimulus values, modified to provide the CIE xhyh and zh values. 

at small, equal wavelength intervals as before but using these new values of the spectral tristimulus 

curves, we obtain X = k2h Eh ?A, Y = k2h Eh yh, Z = kZh Eh FA, where k is a scaling constant, 

and hence obtain new CIE tristimulus values for our test lamp. These values should be the same 

as X, Y, 2, obtained from our experimental values for (r) (b) (g). 

A discussion such as this showing the development of the chromaticity diagram often appears 

somewhat confusing. However, the important points concerning the diagram can be quickly 

summarized without understanding how it was obtained. 

The appearance of any colour, of whatever nature, exclusive of its brightness, can be represented 

by two quantities, x and y, plotted on a two-dimensional graph called the chromaticity diagram; 

these co-ordinates must lie within a figure defined by the spectral hues. Illuminants having 

different spectra can have the same x and y values. 

20 1


White light sources 

The chromaticity diagram was specified in terms of an equal energy spectrum, so for such a 

spectrum of white light, x = 1/3, y = 1/3 and z = 1/3. The white light found in nature does not 

normally have these values. Hence, CIE defined three standard illuminants, A, B and C. 

When a given density of electromagnetic radiation is in thermal equilibrium with matter, as, 

for example, in a furnace, it has a characteristic spectrum called ‘black body’ radiation. If we 

peek through a small hole in a furnace wall, we see this characteristic spectrum, red coloured at 

low temperatures, white when hot - and the furnace temperature at which this colour exists 

is called the colour temperature. Many bodies, such as a filament lamp, or the sun, give approximate 

black body spectra, so CIE found it useful to employ simulations of black bodies at three 

colour temperatures for their standards. 

Standard A was a gas-filled incandescent lamp at a temperature of 2856 K, giving x = 0.4476, 

y = 0.4074, z = 0.1450. Standard B approximated sunlight at a temperature of 4870 K, giving 

x = 0.3486, y = 0.35 16, z = 0.3000, and Standard C approximated daylight, which, because of 

the blue sky, is at a higher temperature 6770 K, giving x = 0.3 100, y = 0.3 162 and z = 0.3738. 

(The three standard illuminants were actually obtained by passing the light from an incandescent 

lamp through filters.) These three points are plotted on the chromaticity diagram in figure 9, 

together with the curve of black body radiation. 

0.8 

0.6 

Y 

500 

0.4 

0.2 

0 0 2 04 06 08 

X 

Figure 9. The CIE diagram for black body radiation at different temperatures in K, showing also the CIE standard illuminants 

A, B and C. 

202

Colour 

Perceptually, if our environment is bathed in light from any one of these sources, we would 

gain the feeling of white. This is because our eye is not a photometer but works by comparison 

and we have nothing with which to make such a comparison if the whole environment has the 

same illumination. This brings up the question asked by photographers why a blue filter is 

necessary over the lamp before daylight film can be used with a filament lamp. After all, we use 

the same eyes both outside and with such a lamp, why cannot the film also be the same? The 

answer lies in the fact that in viewing the film, our colour sense is modified by the environment 

surrounding the image and this would make the colour as viewed too yellow should the film be 

exposed under a filament lamp. 

The Colour of Reflected Light 

So far, we have discussed the comparison of illuminants, which has the advantage of allowing 

us to match the three primary sources and our test lamp under similar conditions. However, in 

practice we are generally interested in the colour of objects illuminated by a particular light 

source. We obtain the values for the primary sources illuminating a block of highly reflective 

material which matches the colour of the object illuminated by the white light of interest, under 

the same geometrical conditions. The material must reflect white light diffusely with large, 

constant efficiency. Often MgO is used. Then the ratio of the Y co-ordinate for the opaque 

material to that for the MgO block is a measure of its reflectance. This is shown diagrammatically 

in figure 2, if we place our test sample over that part of the white screen illuminated by the 

single lamp. The eye matches the light reflected from the test sample illuminated with the 

particular light source, generally one of the CIE standards for white light, with light from the 

three sources providing the primary colours, reflected from a magnesium oxide block. If the 

luminance of the primary sources is (r), (g) and (b), we may obtain X, Y and 2 from these, using 

the equations given before. However, in practice this is rarely done. Instead, a spectrophotometer 

is employed. This device compares the-spectrum reflected from the sample with that reflected 

from the magnesium oxide block, wavelength by wavelength, giving the reflectance of the sample, 

which is the ratio of the intensity of the light reflected from the sample at a specific wavelength, 

to that reflected from the magnesium oxide, taken as 1. Figure 10 shows diagrammatically how 

we obtain the x and y co-ordinates from the reflectance. We take the intensity spectrum of the 

illuminant we desire, multiply this, wavelength by wavelength, with the sample reflectance to 

obtain the spectrum seen by the observer. This is multiplied by the three spectral tristimulus 

plots, sometimes called the ‘colour matching functions’ (figure 8) wavelength by wavelength 

again. The area under the three curves obtained (the integrals) is equal to the X, Y and 2 values, 

and from the ratios of these we obtain x, y and z as before. Hence, we obtain the values without 

interposing a live observer, by assuming the spectral tristimulus plots. 

There are various mathematical techniques for simplifying the rather tedious calculations, but 

the employment of computers has rendered most of these obsolete. If we plot points on the 

trichromaticity diagram, the magnesium oxide should lie at the same point as its white light 

illuminant, if it reflects uniformly. Under these circumstances, Y for the object is the reflectance 

normalized against the magnesium oxide. 

A1 terna tive Co-ordinates 

The trichromaticity co-ordinates are convenient for the physical representation of colour. However, 

most people have little feel for their significance, so three other parameters are often 

employed which are simpler conceptually. 

At this point, we must separate the psychephysically defined quantities of luminance, 

203


X 

X = 14.13 

Y = 1 4.20 

z = 51.11 

Wavelength / n m Wavelength / n m Wavelength / nrn 

CIE Standard Source Object CIE Colour-matching CIE Tristtmcllus 

functions for the 

values 

eq u a I - e ne r g y spectrum 

Figure 10. Method of calculating the CIE tristimulus values X, Y and 2, for light reflected by an object, from the energy spectrum 

of the source, multiplied by the reflection coefficient R of the object, multiplied by the spectral tristimulus values for the equal 

energy spectrum. The area under the resultant curve gives us X, Y and Z. 

dominant wavelength and purity, with the perceptual quantities of brightness, hue and saturation. 

The psycho-physically defined quantities are numbers based on the spectrum of the source, and 

obtained from the CIE diagram. The perceptual quantities are the psychological responses associated 

with these respective quantities, because they depend on things other than the spectrum of 

the source. The study of the physical quantities connected with light and colour, such as the 

power of light in watts per square metre at a given wavelength falling on a surface, is called 

radiometry. The study of the psycho-physical quantities, such as lumens per square metre, is 

photometry. Quantities such as the lumen are specified in terms of a defined average over many 

observers to obtain lumens per watt. However, the psychological response, such as saturation, 

corresponding to the photometric quantity purity, is not defined, and wil depend on the 

observer. For example, change in luminance wil not only alter the perceived brightness of a 

colour there wil also be changes in hue (the Bezold-Brucke effect) and in saturation (the Purdy 

effect). A similar effect in sound is heard when the psychological pitch of a note rises as the loudness 

of the note dies away, though the physical quantity of frequency remains constant. 

Luminance is given by the Y co-ordinate as before. (Reflectance for a reflecting sample.) 

Draw a straight line on the chromaticity diagram from the point representing the white used as 

the illuminant through the point representing our sample, to the periphery of the plot. Dominant 

wavelength is then the spectral wavelength at which this line intersects the periphery. We can 

match the colour by adding a quantity f of light of the pure spectral value involved, to one unit 

of the white light. Purity is the ratio off to the total light (1 + f), i.e. the fraction of pure hue 

in the mixture. 

As an example, look at the point A in figure 7, which is for an orange paint sample. We draw 

a line from the white point, through A until it intersects the periphery at B. From point B, the 

value of the dominant wavelength is found to be 592 nm. The purity is given by WA/WB, which 

is 0.18/0.30 or 60 per cent. 

There is no dominant wavelength for the region directly between red and blue, where colours 

such as purple and magenta lie. It is usual to specify the dominant wavelength of the comple- 

204

Colour 

mentary colours as for the point F of figure 7. The line from the point representing the colour 

on the CIE diagram is extended back through the neutral (white) point to strike the periphery 

at the complementary wavelength at D. The purity is taken as the ratio of the distance from 

the colour point to the neutral point FW, to the distance from the neutral point through the 

colour point to the straight line joining blue (400 nm) to red (700 nm), WE, so the example 

given would have a dominant wavelength of C505 and a purity of 0.53. 

Other Colour-Order Systems 

The CIE chromaticity diagram is a very physical way to represent colour - every possible colour 

can be represented on it. However, when dye chemists talk about the colour of materials they 

may use two other systems. These involve matching, by eye, the swatch of material under consideration 

with a sample of coloured paper. These samples are from the Munsell Book of Color 

[ 21 where they are arranged according to chroma, corresponding to hue on the CIE system, and 

value, which roughly corresponds to saturation. The Ostwald system describes colours by their 

9 

8 

G 

7 

Y 

6 

5 

4 

500 

5 I I 

7 

L 

,- 

c 

1 

3 4 5 6 7 

X 

Figure 11. Satisfactory primary colours. 

205


full colour content, white content and black content, in terms of idealized spectrophotometric 

curves. It is of value for artists and dyers working with mixtures of a coloured pigment with black 

and white pigments. Samples arranged on the Ostwald principle may be found in the Color 

Harmony Manual [ 31 . Basically what one does using these systems is to obtain the closest match 

between the sample and the test material, illuminated by suitable white light, and interpolate 

between samples if necessary. 

Addition of Colours: illuminants 

Returning to the CIE system, the quantitative nature of the tricbromaticity diagram has certain 

advantages. If we obtain a blend of illuminants by shining blue and green lights simultaneously 

on our screen, the combined illumination follows a straight line on the diagram from one source 

to the other, depending on the relative intensities of each. If we pick three illuminants, we may 

combine them in different proportions to obtain colours at any point within the triangle joining 

them. We might think the best primary colours would be those spectral hues providing the largest 

area - 400, 520, and 700 nm (B, G and R of figure 11). In practice, Hardy and Wurzburg have 

shown that the best results are obtained by employing 535 nm for the primary green, because 

then we can obtain a better match with the many saturated yellows occuring in everyday use. 

They suggest the triangle DER of figure 1 1. 

0.8 

0.6 

Y 

0.4 

0.2 

0 0.2 0.4 0.6 0.8 

Figure 12. Least perceptible difference in colour, for a normal observer. (After McAdam.) The axes of the ellipses have been 

multiplied by ten. 

X 

206

Colour Difference 

Colour 

The ability of the normal eye to assess differences of colour is not uniform over the CIE diagram. 

McAdam performed a series of experiments with several observers, leading to the results shown in 

figure 12. The ellipses represent the ability of the eye to detect differences. It is clear that the eye 

is most sensitive to changes in hue and saturation in the blue, Our eyes are not very sensitive to 

changes of saturation in the green, The axes of the ellipses have been multiplied by ten. Colour 

differences are notoriously difficult to specify, which is a nuisance since so much depends upon 

them in the dye and paint industries. Many paint and dye companies depend upon interpolations 

of the Munsell scheme of ordering in terms of hue, value and chroma to specify their pigments. 

To avoid the limitations of human observers, recently both analogue and digital computers have 

been employed to measure colour differences employing spectra obtained from a spectrophotometer. 

1 I bl 

n .2 .3 .4 .5 .E .7 

:< 

.I .2 .3 .A .5 .6 .7 

x 

Figure 13. Defective colour vision. Loci of colou~s confused by protanopes (a) and deuteranopes (b). 

‘Colour blindness’ - Defective Colour Vision 

The CIE chromaticity diagram is based on the fact that the response of normal individuals to 

matching colour is closely the same. However, a small percentage of the population has a reduced 

ability to perceive colours. The mechanism of the retinal process is so little understood that it is 

uncertain whether the causes of abnormalities lies in the malfunction of the retina or the processing 

that follows this. All forms seem to be inherited. Abnormalities are divided into monochromatism 

(‘total colour blindness’), dichromatism (‘partial colour blindness’) in which only two 

distinct hues are sensed, and anomalous trichromatism, where the three colour response differs 

from the norm. The colour response of a monochromatic (a better word would be ‘achromatic’) 

individual is the same for photopic and scotopic vision i.e. high or low levels of illumination. This 

leads to the belief that only the rod cells, which respond to low level illumination, are present in 

such eyes. Dichromatism takes several forms, the effects of two of which, deuteranopia and 

protanopia, are shown in figure 13. Colours lying along the straight lines on these diagrams are 

confused by such individuals. Thus, both would be unable to distinguish red from green, and the 

207


white, or neutral, point would give the same sensation as 497 nm or its complement in the one 

case, and 493 nm in the other. Anomalous trichromatism occurs in about 7 per cent of the male 

population. Some are said to be red weak - red appears very dim in most situations - others are 

green weak. 

APPLICATIONS OF THE CIE DIAGRAM 

A colour television screen is covered with a microscopic array of phosphor dots emitting red, blue 

and green light. The Federal Communications Commission specified the three points B, G and R 

on the diagram of figure 14 as the broadcast standard for the chromaticity co-ordinates. 

.9 

.8 

.7 

.6 

Y 

.5 

.4 

.3 

.2 

.I 

.I .2 .3 .4 .5 .6 .7 

X 

Figure 14. Chromaticity diagram showing the Munsell printed colours of maximum saturation (polygonal figure), the primary 

colours specified by the United States Federal Communications Commission for broadcast (RBG) and the negative primary 

colours used by KODAK in a co1o::r film (CYM). 

208

Colour 

Also shown on the same figure is the outline provided by the cards or ‘chips’ printed with 

Munsell coloured inks, which probably provide the greatest colour purity possible for printing. 

The maximum excursion of purity must lie within the figures. It is clear inks cannot provide 

as great a purity as illuminants such as phosphors, and that least purity lies toward green, where, 

fortunately, the eye is least sensitive to purity. 

Subtractive Colour - Filters 

So far, we have been adding illuminants to provide colours of different dominant wavelength and 

purity. White light may be considered as a combination of points running around the edge of 

chromaticity diagram, excluding the straight line from red to blue. If we filter out all but a small 

segment of the periphery, we get a pure hue, colour of one dominant wavelength, but at the 

expense of brightness, since we are using only a small fraction of the total light output. As the 

region passed by the filter increases, the light transmitted gets brighter, but less pure since the 

centroid of the peripheral points moves inward away from the curve. It is difficult to obtain a 

bright but pure green, for example, because the greatest curvature of the periphery occurs here, 

and since coloured inks work by filtering the white light reflected by the paper, very pure greens 

08 

0.6 

500 

v 

0.4 

0.2 

0 0.2 0.4 5.6 0.8 

X 

Figure 15. The lighter a colour is, that is, the more light it reflects, the more restricted its chromaticity range. Here, the 

‘McAdam limits’ of the chromaticity of real colours, viewed in daylight (CIE Source C) is shown for different values of their 

luminance Y. It is essentially a contour plot, the ‘altitudes’ being the maximum reflectance. 

209


are not found in printing. An ink which filtered only the peak green would be too dark, or 

absorbent, to be of value. Blue and red also cannot be obtained both bright and pure, since we 

can only widen our filters in one direction, which shifts the dominant wavelength away from the 

end. The colour most easily obtained both bright and pure is yellow; when widening our filter 

to include from E to R in figure 11, the centroid wil still be close to the periphery. Yellow is 

very important to the artist for this reason. Our perception of yellow is also unusual - for 

example, there is a smooth gradation from blue through cyan (turquoise) to green - so cyan 

might be called a bluish green, but who would call yellow a reddish green? We shall meet this 

again in the Hering theory of colour vision. 

The quantitative aspect of what we have said is shown in figure 15. This shows the limits of 

purity for real colours for daylight illumination. It indicates we can employ a filter which will 

allow 80 per cent of daylight through and still obtain a pure yellow. Since white light contains 

all dominant wavelengths, in principle a filter can be designed to separate from it light represented 

by any point on the chromaticity diagram. It is found that three filters can be used in 

combinations to cover most of the diagram. These filters are sometimes called the negative 

primary colours; cyan, which is blue-green and removes red light from the spectrum, so it is sometimes 

called minus red; magenta, which subtracts green and allows red and blue to be transmitted; 

and yellow, which removes blue and allows green and red through. The position of the colours is 

marked on the chromaticity diagram of figure 14; the specific points represent dyes employed in 

a Kodak colour film.If a cyan and magenta filter are placed over a white light, a blue colour is 

transmitted. This can be seen quantitatively from the distorted triangular curve of figure 14, 

which passes through C, M and Y, and represents the colour transmitted by the filters in pairs of 

different intensity. Superposing illuminants in pairs of differing intensity defines a straight line 

between them. However, superposed pairs of filters do not specify such a line. The Kodak film 

employing these dyes can reproduce all colours within the triangle. Because the colours provided 

by the phosphors of a television screen and colour film do not match exactly, colour movies 

sometimes give a poor representation on television. Special film manufactured specifically for 

television is now employed. 

A consideration of the colour photographic process indicates the advantages of negative 

primary colours. 

The first colour photograph was made by James Clerk Maxwell in 1855. He obtained three 

identical photographs of a tartan ribbon, except that one was exposed through a blue, one 

through a green, and one through a red filter. Positives were made and projected onto the same 

Camera takes three pictures 

through filters here 

,/red 

filter 

ir T iage 

r 

screen 

Figure 16. Maxwell's experiment in colour photography. 

210

Colour 

screen, that taken through a blue filter being projected through a blue filter, green through green 

and red through red, as shown in figure 16. An accurate rendering of the scene would have been 

obtained were it not for the fact that the plates in use at that time were not red sensitive! This is 

an additive colour process, but it is obviously very cumbersome. The simple Dufay autochrome 

process yielded delightful results at the turn of the century, the principle being the same. 

Minuscule granules of starch (figure 17) were dyed blue, red and green, and acted as primary 

filters superposed, side by side, over the film and pressed into it. The film was exposed to the 

scene, developed and reversed so that, if exposed to a red scene, the silver deposited under the 

red granules would be dissolved away, but not under the blue or green granules. The filmwould 

then appear red, as it should. The big disadvantage of this process was that, even for a white 

scene, two thirds of the light incident on the film was absorbed, since each granule absorbs twothirds 

of the light incident on it, the red, for example, absorbing blue and green. The more 

recent photographic processes avoid this problem. The principle of modern colour photography 

involves a three-layer emulsion, the outer layer being sensitive to blue light, the second layer to 

green and the third to red. Let us take a picture of a flag having blue, green and red stripes, as 

shown in figure 18. The film is developed, removing the silver from the exposed silver halide. A 

second stage of development then takes place. The conversion of the remaining silver halide, left 

in regions of low exposure, to silver occurs, with the release of dyes in the emulsion which are 

complementary to the colours to which each layer was sensitive. The silver is now dissolved away 

leaving only the dye. Now, for white light, all layers would be exposed, and the silver removed 

at the first development, leaving none for the second, so no dye would be released, and the film 

would be transparent and colourless. For the flag we took, the colours wil be produced as shown 

in the figure, for example, the top layer wil be exposed by the blue stripe, but not the bottom 

two layers, so dye will not be released in the top layer, but wil be released in the layers dyed 

magenta and cyan, which only allow blue through. For the green stripe, the centre, magenta 

layer, which absorbs green, wil be clear, and the red stripe wil expose the bottom layer, which 

wil be clear, allowing the yellow and magenta layers to be dyed, so only red gets through. 

blue light 

blue transparency 

transparent backing 

light 

Figure 17. The autochrome colour photography process. Light traverses small, dyed starch granules. 

It is clear from this example of colour film why this system is called a subtractive process. 

Whereas, with the additive process, we start with a dark screen, and illuminate it with blue, green 

and red primaries to obtain our match, with the subtractive process we start with a white light, 

as in a projector, and subtract blue, green and red with yellow, magenta and cyan filters respectively, 

until we obtain the colour we desire. Note again that earlier colour processes, such as the 

autochrome discussed above, only allow a maximum of a third of the white light incident on the 

colour slide to pass through, whereas the newer processes can let almost all of it through. 

21 1


Kodachrome 

Yellow filter removes blue 

Blue sensitive layer 

reen sensitive layer 

Red sensitive layer 1 

Film 

Develop 

Expose and redevelop wlth dyes 

This reverses the film and dyes it 

R B G R B G R E G 

Red + !Blue 

White 

+ 1 Green 

Yellow {absorbs blue I 

Magenta (absorbs green1 

h 

6 Cyan [absorbs red I 

Colours complementary 

t~ those for which fllm 

was sensitive 

Figure 18. Modern colour photography process, using complementary colours. 

\. 

212

Colour 

I 

120 

Noon Summer Sunlight 

5740K 

--I 

4O F 

Noon Winter Sunlight 

01 I I I I I 

400 500 600 

Wavelength/nm 

Figure 19. Sunlight at different times of the year at mid latitudes. 

Sources of Light 

We have said very little about the nature of light sources so far, because we wished to introduce 

the CIE chromaticity diagram first as a means of specifying their colour. Daylight itself is a very 

variable quantity, as shown in figure 19 for sunlight. North light, or the blue sky, which is sunlight 

scattered by small particles in the atmosphere, can exceed 7000 K colour temperature. 

Fluorescent light comes from mercury discharge tubes, which give only single lines in the 

spectrum, as shown in figure 20. Fluorescent powders inside the discharge tube modify this to 

give a white light spectrum. 

200 300 400 500 600 700 

Wave I e ngt h /nm 

Figure 20. Line spectrum of a low pressure mercury vapour lamp. 

213


Dyes, paints and pigments 

The perceived colour of an object depends on the combination of the spectral energy distribution 

of the light source, the spectral transmittance or reflectance of the object on which the light falls, 

the spectral response curve of the eye - and the psycho-physical process of comparison which 

the eye uses to determine colour. We wish to study the way light is modified by seen objects, 

when the observer and light source remain fixed. It is the colourants, dyes and pigments added to 

fabrics, coated on wood or metal with the aid of a binder, or medium, or embedded in plastic, 

which do this. They selectively scatter and absorb light, changing the incident spectral energy 

distribution. Dyes were originally defined as water-soluble substances used to colour material 

from aqueous solution, while a pigment was an insoluble material, generally a ground-up inorganic 

powder, dispersed in the medium to be coloured, which was then applied to a painting. Modern 

technology has made such distinctions more complex with the introduction of organic dyes and 

acrylic paints. 

1 0 

08 

08 

Y 

a, 

06 

c" 06 

ID 

U 

? 

04 E 

cn 04 

C 

ID 

L 

t- 

02 

02 

00 02 04 06 0.8 

X 

400 500 600 700 

Wavelength In3 

Figure 21. The change in colour with concentration of a blue dye, whose transmittance spectrum is shown. The colour moves 

away from the white point C as the concentration increases. (After EVANS, R.M. [6] .) 

Dyes, being transparent, work basically by absorption, in much the same way as the filters 

discussed earlier, so in principle the calculation of the colour produced by different concentrations 

and mixtures of dyes is straightforward. Because it is necessary to calculate the effect of 

the mixture at each wavelength, the advent of the digital computer has greatly speeded up 

the calculations. According to Beer's Law, the logarithm of the transmittance T (the fraction of 

light transmitted) is given by multiplying the concentration C of the colourant by its absorption 

coefficient A (the fraction of the light absorbed at unit concentration) 

log T= - CA 

There is a simple logic behind this. If a single filter cuts the light to one half, then it is clear two 

thicknesses will reduce the light to half as much again, or to 1/4, and three thicknesses to 1/8. 

214

y move in the direc 

value of the wavelength on the periphery of the chromaticity diagram. 

Scattering 

mixing dyes, with no scattering, 

With mixtures of paints, however, s 

simpIe-subtractive, can therefore be 

e very important. 

Scattering introduces yet ther complication. One of the principal criteria of a paint which 

invoIves scattering is good ering’ or ‘hiding’ PO y the mass of paint per 

unit area to obscure a black and white chequerb 

Except for black, or very dark 

paints, the covering power is determined in part b 

g power of the pigment particles. 

In the past, this was often lead white (basic lead carbonate, refractive index 1.94-2.09) in linseed 

oil (refractive index 1.48). The poisonous nature of the lead salt caused it to be replaced by 

titanium dioxide. The oxide is of high refractive index (2.6) but quite transparent. Hence, it 

acts as a white paint purely by virtue of scattering all the wavelengths of light, for which its 

refractive index must be very different from the medium in which it is embedded. It is for a 

similar reason that ground glass looks whit;. 

0 0.5 1.0 1.5 

Particle size/wavelength 

Figure 22. Scattering as a function of particle size for titanium dioxide. 

215


In much the same way as a half wave antenna provides the best length to absorb and reradiate, 

or scatter, radio waves, the best size for titanium dioxide particles is a half wavelength of light. 

Figure 22 shows a plot of scattering versus wavelengths for different particle sizes. Very small 

and very large particles do not scatter well. Suppose we mix a grey dye with our white scatterer, 

as shown in figure 23. The grey absorbs equally throughout the spectrum. If the white pigment 

scatters more in the red than the blue, the red light wil not penetrate very deeply into the paint 

before it is scattered back out. On the other hand, blue light will penetrate more deeply before 

it is backscattered, and in doing so wil be absorbed. Hence, the effect of mixing the white 

pigment and the grey dye wil be to produce a red paint, a quite unexpected result. 

Blue 

Red 

t 

100per cent 

Reflected 

100per cent 

White Pigment 

with no absorption 

Blue 

Deep Penetration 

1 leads to absorption 

Red 

very little 

absorbed 

White Pigment 

I' 

J 

Figure 23. Scattering by a white pigment, undyed, and with a grey dye. 

216

Surface Reflection 

Colour 

The surface of a paint may be smooth and give a specular reflection, which is generally fairly 

uniform and reflects white as white, as with a mirror, in a specific direction. However, it may be 

matte, and give a diffuse reflection, which generally involves surface penetration, in which case 

the colour of the pigment primarily determines the colour of the paint. 

.9 

.8 

.7 

.6 

Y 

.5 

-500 

I 

.4 

.3 

.2 

.I 

.I .2 .3 .4 .5 .6 .7 

X 

Figure 24. Chromaticity diagram, showing mixtures of Dana tempera (poster paint), Y: ‘spectrum’ yellow, R: ‘spectrum’ red, 

B: ‘spectrum’ ultramarine blue, G: emerald green, M: magenta, RV: spectrum red violet, T: turquoise blue. The straight lines 

plotted vertically represent the brightness of the colour (Y) of that point. 

217


Artists versus physicists - the primary colours 

Artists are vehement that red, yellow and blue are the three primary colours, whereas physicists 

believe these are red, green and blue. If we assume that a bluish-turquoise is called ‘blue’ by 

artists, and a reddish-magenta ‘red’, we could say that in fact, artists were merely employing the 

negative primaries, and paints behaved like dyes. Unfortunately, paints are not that simple. 

Figure 24 shows what happens when we mix differing quantities of blue, red and green, and blue, 

red and yellow poster paints in pairs. As will be seen, the area of the CIE diagram circumscribed 

by these mixtures is much larger with yellow than with green. Although paints behave largely 

as dyes, and hence act as subtractive filters, nevertheless, there is also an additive component. 

This may be seen if we imagine the pigment particles to be completely opaque. Then, looking 

at the surface, we would see a series of dots of one colour or another, which would combine 

additively in the retina. Seurat made use of this effect in his ‘Pointillist’ paintings composed 

of little dots of paint, which appear separate when examined close, but combine when we move 

back to view the picture. 

Cornea 

S 

Figure 25. Horizontal cross section of the right eye. 

THE PHYSIOLOGY OF COLOUR VISION 

The physics, physiology and psychology of the eye are interwoven. The physical part of vision 

consists largely of focusing the object being viewed onto the retina, in much the same way as 

does a camera. Most of the refraction or bending of light as it enters the eye occurs at the cornea, 

as shown in figure 25. This is because the refractive index of the main body of the eye, being 

composed of an aqueous fluid, is approximately 1.33. The cornea itself has a refractive index of 

1.37 and a radius of curvature approximately 7.8 mm. The light passes through the aqueous 

ugh the so-called crystalline 

ed by the fluids contained 

218

Colour 

index of 1.4, it is flexible, and it is the alteration of shape of this lens from fat to thin by muscles 

within the eye which allows us to focus on nearby or distant objects. For distant objects the 

front surface of the lens has a radius of curvature of about 10 mm, the back surface 6 mm. When 

focusing on nearby objects, the front surface can bulge to less than 6 mm radius. Light is focused 

through the vitreous humour onto the retina, which is composed of light sensitive cells. Nerves 

go back from these cells into the eyeball, and emerge through the blind spot, from whence they 

run to the brain. Curiously, light must pass through these nerves in order to reach the sensitive 

cells. No one would design a television camera so that the light had to pass through the wires 

to reach the sensitive surface, but the inside-out nature of our visual process arises as a feature 

of the evolutionary process. 

The opening of the lens is determined by the iris diaphragm, controlled by a set of involuntary 

muscles. Look into a mirror, and suddenly shine a bright line into your eye. The iris diaphragm 

closes within a fraction of a second, reducing the size of the pupil and the amount of light entering 

the eye. It takes much longer for the iris to relax on entering a darkened room. With the iris 

contracted, as on a bright sunny day, if we look at a white sheet of paper, we can see the shadows 

cast on the retina of bits of muck, called ‘musca volentes’ floating in the vitreous humour. 

H- 

H- 

H- 

H I / 

H-C 

I 

H-F\ H 

H 

H-C-H 

I 

H C 

C C 

I 

I 

I/ \\ A 

I I M A 

C 

I\ /C-c-H 

H C-HI H 

I 

I CrH 

AH 

H I 

H -C -H 

I 

/[ 

C 

H 

c 

/\ 

C-H 

Retinene in Darkness 

H 

H 

I 

I 

C-H H H - C-H 

I 

I 

C 

\\ 

C C I 

I Y H H 

/C-C-H I 

C-H I H 

I C,-H 

IH 

H 

I 

H C 

I / \\ 

H -C C-H 

I 

I 

H C 

I\\ 

H O 

H I 

Retinene in Light 

H-C-H 

I 

/A 

H 

C ,[\C A 0 

Figure 26. Molecular structure of the retinene group of the rhodopsin pigment. The structure is twisted as shown in the top 

portion in the dark. Absorption of a light quantum causes the structure to straighten out. 

I 

H 

I 

H 

219


The retina itself, comparable to the film in a camera, is composed of rod-shaped and coneshaped 

cells, each about 0.08 mm in diameter. The active light sensitive element for the rodsis 

the chemical compound rhodopsin. The molecular structure is shown in figure 26. When light 

strikes the rhodopsin pigment, the retinene group is caused to swing round in the molecule, 

changing its potential energy, and setting off an electrochemical impulse in the retina's nerve 

cells. The rhodopsin bleaches under illuminaticn and is restored in the dark. The light, having 

transferred its energy, ceases to exist. The electrical impulse from the retinene appears to be of 

too low a voltage to trigger the neurons, so it appears there is some unknown intermediate 

amplifying system. The structure of the retina is shown in figure 27. Each sensory cell is attached 

to one or more optic nerve fibres or axons via the synapses, bipolar cells, and amacrine cells. As 

will be seen, there is not a one to one relationship between a rod or cone, and an axon. In addition, 

experiment shows that the nature of signals transmitted along the axons is different from the 

three colour output of the cones described below. The nearest analogue is the way in colour 

television the three colours are transmitted via a black and white and chroma signal. In the case 

of the eye, the output appears to be black-white, red-green and yellow-blue. 

optic 

nerve 

fibres 

Ganglion 

cells 

Inner 

syn a p t ic 

layer 

Amacrine cells 

Bipolar cells 

Horizontal cells 

Outer synaptic 

layer 

Receptor 

nuclei 

Receptors 

pigmented layer 

(epithelium cells) 

.c 0 ne 

- 

rod 

INNER 

LAYER 

MIDDLE 

LAYER- 

OUTER 

LAYER 

Figure 27. The structure of the retina. 

Optical properties of the cone cells 

The ends of the cone cells through which the light first passes have three times the diameter of 

the opposite ends. Since light from the pupil enters roughly parallel to the length, it is totalinternally 

reflected from side to side, as shown in figure 28, and concentrated on the smaller area 

which, it seems, is the part of the cell containing the photosensitive pigment, less of which is 

required because of this focusing action. 

220

Colour 

- 

Light 

Incident + 

From Iris 

Cone Cells 

1 

J 

rl 

1 

Figure 28. Trajectory of light in the cone cells. 

The absorption of light by the visual pigment in the cones has been measured and is shown in 

figure 29. The three types of spectral absorption curve are thought to be the source of three 

colour vision. The active substance is called ‘iodopsin’, but its exact chemical nature is still 

unknown. 

Wavelength/nm 

Figure 29. Percentage absorption of light of different wavelengths by the dye present in the three types of cone cell of the eye 

in primates. 

22 1


I:/ 4- 

Dendrite 

Each neuron, by which the signals are transferred to the brain, consists of a cell body (figure 

30) which is the nutrient centre of the cell, and from which extend two filamentous structures. 

One of these, the dendron, or dendrite, is short and much branched. The other, the axon, is an 

elongated filament with a branched end. Signals originating at the dendrite end pass through the 

cell body and along the axon to its termination. The signals are short, more or less uniform 

electrical impulses, travelling many metres per second. The relay from the axon termination of 

one neuron to the dendritic termination of the next neuron is called a synapse. The transfer of 

signal at this point appears to be chemical rather than electrical, and a millisecond is required for 

the chemical diffusion over the gap of about one micron. Intensity of light falling on the retina 

is perceived not by the size of nerve impulses, but by their number. The frequency of impulses 

varies more or less as the logarithm of the stimulos intensity. Only one kind of information may 

be transmitted along one fibre. 

As wil be seen from figure 27 there are many t s of cells between the rods and cones and 

the optic nerve fibres. It is not clear what many o e do, but it appears that the middle layer 

of cells, .specifically the horizontal and amacrine cells, in some way interconnect the rods and 

cones laterally. The effect :bf this on colour vision is that the signals emerging from the eye are 

not directly related to the red-blue-green impulses which the three types of cone produce. 

Instead, some ganglion cells from which neurons emerge show a response firing when green light 

illuminates the retina, but inhibited under red light. Other cells give a ‘green off-red on’ response. 

Figure 31 shows typical responses for a neuron coming from a ganglion. This ‘opponent colour’ 

coding system was developed by Ewald Hering to give a colour vision theory involving yellowblue, 

red-green and black-white receptors, with the idea of accounting for two-colour phenomena 

- such as the fact that red and green (or blue and yellow) vary together in sensitivity and never 

appear subjectively mixed - i.e. our senses tell us turquoise, or cyan, is a blue-green, but who 

would suggest that y w is a greeny-red? This cannot be explained by the Young-Helmholtz 

three colour theory. 

222

Colour 

C 

0 L 

3 

a, 

z 

E 

L 

U 

J 

Q 

e, 

J 

0 

Figure 31. A ganglion cell response, as measured by a probe, as a function of wavelength. Darkness is followed by a half-second 

light flash. At short wavelengths there is an ‘on’ response. 

Neurons leaving the eyes via the blind spot meet at the optic chiasma, where nerves from the 

right hand side of each eye combine and go to the right side of the brain, and nerves from the 

left hand side of each eye go to the left side of the brain, as shown in figure 32. They first enter 

the lateral geniculate bodies, which, in addition to synthesizing binocular vision also have a bearing 

on colour vision. The signals proceed from there to the visual cortex, the outer convoluted 

part of the brain. Resear rs have mapped out the area of the cortex associated with each part 

of the retina. 

In discussing the CIE chTomaticity diagram, 

d between normal observers. 

standard conditions, as it is i 

ted by its surroundings, by ho 

n. We explain some of these 

e seen good agreement on matching colours 

er, colour is not ordinarily observed in small 

for the diagram, and our perception of colour 

g we observe the colour and by the nature of 

s by adaptation, but it is very difficult to 

Colour Adaptation 

Three types of adaptation have been distinguished: local adaptation, lateral adaptation and 

general adaptation. 

223


geniculate 

[enlarged 

ortionatelyl 

- Visual cortex 

Figure 32. The relationship of the eye to the brain. 

Local adaptation - afterimages 

Observation of intense coloured areas for any length of time affects subsequent vision on the 

corresponding areas of the retina. If we stare fixedly at a yellow object and shift our gaze after 

twenty seconds to a neutral background, we shall see the complementary colour blue. This afterimage 

is due to local adaptation. In the area of the retina where the yellow field was first imaged, 

the sensitivities of the green and red receptor systems were reduced by prolonged exposure to a 

mixture of red and green light. Thus, when the yellow field was replaced by a sheet of white 

paper, red and green were subtracted from neutral white, leaving a blue image. As the receptor 

systems recover their sensitivities, the afterimage fades. 

Lateral adaptation 

A turquoise object having a green background appears bluer than when placed against a blue 

background, which gives it a green tinge. Further, it appears lighter against a black background 

than a white one. 

General colour adaptation 

In viewing a given scene, the visual system adapts its colour sensitivity in such a way that the 

224

Colour 

illumination appears colourless. This power of adapting to the colour quality of the prevailing 

illumination is known as general colour adaptation. By means of it, we become less aware of the 

physical conditions existing at the time. Thus we are not ‘misled’, for example, to the conclusion 

that objects seen at sunset are actually ruddy in hue, or that our companions’ complexion under 

candlelight is yellow. Colourfilm, having no such built in adaptation, gives good results only when 

exposed under illumination of the quality for which the film was balanced, as mentioned below. 

Retinex theory of colour vision 

The crux of the problem of colour vision lies less in the primary process (there can be no doubt 

that, under normal illumination, the cones, with their three ranges of spectral sensitivity in the red, 

green and blue, provide the initial response) but with what happens in the retina, the pathway to 

the brain and the visual cortex afterward. The eye is not a spectrophotometer, recording light 

levels and sending them to the brain - it is much more like a minicomputer backing the process 

of detection of light - and it does this by a complex system comparing the impulses from various 

parts of the retina. A model of such a system is the ‘retinex’ theory of colour vision discussed 

by Edwin Land. We have already seen how the ganglion signals emerging from the retina are 

coded differently from the anticipated response of the individual detector cells. Furthermore, our 

psychological perception of colour is, again, quite different from what the ‘photometer’ picture 

of the eye might give us. As an example of the necessity for a theory of this nature, let us return 

to colour photography. It is well known that two types of film are normally available, one for 

outdoors and the other for incandescent light illumination. We say the latter is for a lower colour 

temperature. Yet, why should this be necessary? If we enter a room under incandescent light, we 

do not obtain the impression that everything is tinged with red or yellow, as is the case for a 

colour slide made of that room using daylight film.Obviously, our eyes compensate in some way 

for the different illumination, and Land points out that the ability for this compensation is 

surprisingly large. One may see this compensation in an achromatic experiment where we hang 

a piece of black velvet nearby, and a sheet of white paper further away. We can now illuminate 

the velvet and its surroundings so that a photometer tells us that the velvet is giving out more 

light than the white paper - yet the paper still looks white, and the velvet black. It appears the 

eye makes a series of comparisons between the velvet and the paper, and takes account of the 

illumination becoming dimmer as we approach the paper, Land refers to this property of an 

object as ‘lightness’ - thus, the paper is lighter than the velvet, even though the latter may give 

out more light. This is a perceptual, not a physical quantity - it is based on the assessment of 

several experimenters. It is detected even under extremely low levels of illumination, when only 

one set of sensors, the rods, is excited. Returning to coloured objects, we wish to relate the 

perceptual quantity of ‘lightness’ with its physical equivalent. Over a long series of experiments, 

Land’s subjects matched irregular rectangular blocks of colour of various kinds called ‘Mondrians’, 

after their resemblance to paintings by that artist, with chips from the Munsell Book of Color [2l , 

a colour-order system. By illuminating these colours with three narrow bands of the spectrum 

at 630, 530 and 450 nm in different proportions, it was possible to show that the physical 

property of reflectance appeared to be associated with lightness - both the Munsell chips, and 

the blocks of the Mondrians reflected the same proportions of 630, 530 and 450 nm wavelengths, 

irrespective of the nature of the incident illumination, which was different for both. A mechanical 

picture of the way in which the retinex system might analyze the retinal output to perform such 

a trick has been proposed. It is suggested that the eye is very sensitive to changes in light yields 

over the edges of objects in the field of view. Thus, the eye takes the three highest outputs 

relevant to the three types of cone and compares everything else to them, taking the ratio of 

reflectances over each edge, but ignoring the change in intensity which occurs over the body of 

the object. Effectively, it traces a path from the object with the highest reflectance, to the object 

225

New Trends in PhysicsTeaching IV 

being observed, multiplying the change of output at each edge, but ignoring slow changes of 

output over smooth surfaces. 

e eye is able to ignore changes in the illumination, both spectrally and as a 

since the ratios discussed wil remain fairly constant. What mechanism in the 

o make such comparison is still uncertain. Lightness, then, is associated with 

reflectivity for the three spectral sensitivities for which experiment has shown the cones respond. 

REFERENCES 

1. NEWTON, Sir Isaac. 1704. Opticks. New York, Dover Publications, reprinted 1952. 

2. MunsellBook of Color. Baltimore, Md., Munsell ColorCo., 1929. 

3. Color Harmony Manual. Chicago, Ill., Container Corporation of America, 1948. 

4. PEASE, P.L. Resource Letter CCV-1: Color and Color Vision. American Journal ofphysics, Vol. 48, NO. 11, 

November 1980, p. 907-17. (Presents a very full and comprehensive listing of books and articles, together 

with a brief discussion.) 

5. BILLMEYER, F.W.; SALTZMAN, Max. Principles of Color Technology. New York, Interscience, 1967. 

6. EVANS, R.M. An Introduction to Color. New York, J. Wiley, 1948. 

7. OPTICAL SOCIETY OF AMERICA. THE COMMITTEE ON COLORIMETRY. The Science of Color. New York, 

Crowell, 1953. 

8. BOUMA, P.J. The PhysicalAspects of Colour. New York, St. Martins, 1971. 

9. Color as Seen and Photographed. (Kodak publication No. E-74.) 

10. AGOSTON, G.A. Color Theoy and its Application in Art and Design. Berlin;New York: Springer - Verlag, 

1979. 

226



C.A. TAYLOR. 

OPTICS LOST? 

During the period between the two world wars it was normal to find the teaching of optics, both 

at the Universit ance end of school and thro 

Fresnel and Fraunho 

ealt with interference, 

through uniaxial 

But look for a moment at the exciting things t 

first World War in the much wider field that we should now regard as optics. In 1801, Young 

ple tank, among other techniques, to demonstrate interference and the acceptance of 

the wave theory beg Polarization by reflection was discovered; Young planted the idea of the 

transverse nature of t waves; Kirchhoff introduced the notion that emissivity bsorp 

are related; Faraday lectured on the idea of ‘fluctions’ in a magnetic field; Ma deve 

227


encouraged nuclear physics almost to the exclusion of other topics, and his disciples fi1lX.d 

many of the important chairs of physics. This, together with the exciting developments in Low 

Temperature physics and the growing interest in the Solid State physics, became the dominant 

topic and optics was almost squeezed out. 

In actual fact, a great deal was going on between the wars that we should now recognize as 

optics. The Braggs were developing the art of X-ray crystallography; ultra-violet and infra-red 

spectroscopy were beinp developed; the seeds of radar and of radio astronomy were being sown. 

But these were scattered topics; they did not have much influence on teaching in Universities 

and Schools and they would not have been included in a conventional optics course. I would 

contend therefore that, although optics appeared to be lost, it would be better to describe it as 

dormant or eclipsed. 

THE RESURGENCE OF OPTICS 

It is always difficult to pin-point the crucial ideas or experiments in the evolution of a subject 

until long afterwards when, with hindsight, one can begin to see the whole path of development. 

But it seems clear to me that the resurgence of optics as one of the dominant fields of 

physics began round about 1950. 

Many factors began to come together in the period 1950 to 1970 which can be seen either as 

a complete revolution - or, as I prefer to think of it - as a re-recognition of the excitement and 

significance of the much earlier discoveries, a taking-up of the story that was set on one side in 

the thirties and forties. The factors that came together were the development of radar to the 

point at which it became not merely ‘radio-direction and range’ but an imaging system; the 

development of television systems which play an important role in imaging by most radiations; 

the development of digital computers which permitted the computation and design of lenses with 

a performance beyond the dreams of opticians of even thirty years ago; the practical realization 

of stimulated emission in lasers; the vast financial expenditure on the space programme which 

needed highly developed image processing techniques; advances in solid-state physics for detecting 

radiations of all kinds; and, perhaps most important of all, a full recognition of the importance 

of information processing, information exchange and the key ideas of band-width limitation. 

This, in turn, led to the search for ever higher frequencies for communication, culminating in the 

modern use of optical fibres and laser light which certainly wil be a general method of communication 

by the end of the century. 

SHOULD NOT MODERN OPTICS BE REGAINED AS A SIGNIFICANT COMPONENT IN THE 

PHYSICS SYLLABUS? 

I am quite convinced that it is high time that optics was put back as one of the dominant features 

of the physics syllabus in both schools and Universities. The potential is enormous and it fills so 

many of the desirable criteria for a course which can be both intellectually demanding and at 

the same time put over to the less able students through exciting and dramatic demonstrations. 

In the first place, I think that it is of paramount importance that everyone should know and 

appreciate something about the way in which we gain information about the world around us. 

The eye-brain system is one of our principal channels for collecting, sorting, remembering and 

using information, and a proper understanding of its potential and of its limitations is important. 

One of the advantages of basing a course on this kind of topic is that it has obvious appeal to all 

228


human beings since we all use it. But it is also of special importance to scientists because one of 

their aims is to by-pass the more subjective elements and arrive at objective conclusions; this 

objectivity can only be achieved if we understand the nature of the subjective complications. 

This approach to optics thus fits in well with the notion that physics courses should be designed 

to be equally appealing to generalists and to budding scientists. 

Optics offers a fine medium for bringing together a large number of apparently different 

topics and of demonstrating their interconnections. A personal illustration wil perhaps make 

this point quite forcibly. During the second half of the Second World War I was working for the 

British Admiralty on the problem of radar jamming. This was the period when radar systems were 

moving to higher and higher frequencies and devices such as wave-guides and horns began to 

replace coaxial cables and arrays of di-poles as radiators. The problems were new, but I was able 

to come to terms with quite a few of them by using my knowledge of optics; wave guides with 

radiating slits were to me merely diffraction gratings; circularly polarized radiators were half 

wave plates and nicol prisms! Thus my optical knowledge helped me to talk quite sensibly with 

radio engineers and to make significant contributions. Later in life, I began to work on crystal 

structure determination using X-ray diffraction and, here again, optics came to my aid; the 

recognition that the apparenly formidable computations of the crystallographer are merely doing 

what a lens does for visible light gives powerful insights into the potential and limitations of the 

subject. Finally, my experiences in experimental optics led to an appreciation of the mathematical 

processes underlying a great deal of modern optics - namely Fourier Transformation - and this 

in turn stood me in good stead for understanding problems in Musical Acoustics which involve 

essentially the same mathematical processes. 

There are many other arguments that could be brought to bear but I think, on balance, it is 

best to let the subsequent sections on the various possible topics speak for themselves. Let us 

start by looking again at some of the key ideas that have provided the basis for modern optics. 

THE SEEDS ARE SOWN 

It is difficult to know where to start a historical excursion, but since a good deal of my research 

life has been spent as a crystallographer I think I shall start in 1669 with the discovery by 

Bartholinus in Copenhagen of the phenomenon of double refraction in Iceland Spar. This remains 

for me one of the most fascinating of natural phenomena and I keep a small crystal - picked up 

for a few francs in the flea market in Paris - on my desk for the sheer pleasure of seeing whenever 

I wish the remarkable doubling of the image. But, of course, it is very much a key discovery 

in piecing together our ideas on the transverse nature of light - though these deductions did not 

follow till much later. 

My next milestone must, I think, be Grimaldi’s work on diffraction. He was only 45 when he 

died in Bologna and his major work was published in 1665 - two years after his death. His 

experiments resembled Newton’s experiments using a prism to analyze a beam of sunlight coming 

through a shuttered window into its spectral components. But Grimaldi used only a pin hole or a 

slit in the shutter and observed that, as the hole was made smaller, or the slit narrower, the bright 

patch at first decreased in size but subsequently grew larger again and that the dark edges became 

coloured. 

Newton first published some of his ideas on light in 1672 but his major work - Opticks [3] 

did not appear till 1704. Fortunately, it is available in a modern reprint form and well repays 

study. I can remember being guided to dip into it by my physics teacher at school when I was 

only about 16 and being completely fascinated by the clarity and thoroughness of his descrip- 

229


tions - especially of the pheno 

For example I have heard peop 

the spectrum of white light; but 

indefinite variety of intermediate g 

But the most surprising, and wonderful compo 

can exhibit this. ‘Tis ever compounded, and 

mixed in a due proportion. I have o 

converge, and thereby to be again 

produced light, entirely and perfectly white. . . . 

This experiment - the reco 

but, surprisingly, many exposit 

Huygens’s principle - first described in 1690 in his Trait6 de Zu Zurnibre [4 

key idea and sowed the seeds for the bridging of the gap in understanding 

geometrical behaviour of light rays and the wave-physics of which they are a 

find it remarkable that Huygens could proceed so far in laying firm found 

explanations of phenomena as yet undiscovered could later be explained. Am 

of course he provided a useful explanation of the double refraction phenomena o 

Fresnel, Arago, Fraunhofer 

who is usually credited with t 

because he used a ripple tank as an analogue in order to explain his ideas and it ga 

particular delight some years 

original ripple tank. He picked up Gi-imaldi’s ideas and recognized, among other things, 

phenomena we generally designate separately as interference and diffraction are inte 

waves are diffracted by an object and subsequently interfere to form a pattern. 

I shall now make another jump - of seventy years - no doubt incurring the wrath of many 

people who feel that other nineteenth century optical workers should have been highlighted. My 

next sower of seeds is Abbe. The use of the microscope had become a popular Victorian recreation 

and the annals of the various Microscopical and Natural History Societies in the latter haif 

of the 19th Century are full of accounts of fascinating phenomena. But, in most cases, the 

observations are merely recorded and not interpreted. Abbe, however, was interested in interpretation 

and his classic paper on the diffraction theory of the microscope (1873) is really the 

key paper from which follow most of the modern ideas on imaging, information, image processing, 

etc. An English translation by Fripp (1875) is a useful source for those who cannot read the 

original German [ 53 . 

It was Porter’s presentation [ 61 of Abbe’s theory that was read with such profound consequences 

by Sir Lawrence Bragg. He recognized the essential relationships between the interpretation of 

the X-ray diffraction patterns of crystals - discussed by Friedrich, Knipping and Laue in 1912 - 

and the production of an image by a microscope, The building up of images of atomic locations 

in crystals using ‘Fourier Synthesis’ became a regular feature of X-ray diffraction studies and was 

really the base, sometimes implicit, sometimes explicit, on which our ideas of imaging were 

developed. Indeed, experiments performed by Sir Lawrence Bragg and Henry Lipson during the 

Second World War on the production of images and atomic dispositions by optical synthesis were 

really the first examples of holography; they were no called and were very special cases - but 

the essential principles were a 

Einstein made a prediction in 1916 that is certainly one of the essential sources of modern 

optics. He concluded that, in addition to the process of absorption of radiation with an increase 

230


of energy, or the spontaneous emission of radiation from an atom in a higher energy state, there 

must also be a third process of interaction called ‘induced’ or ‘stimulated’ emission. He predicted 

this entirely on the basis of thermodynamic considerations - it is, of course, the key idea on 

which the laser is based. Further theoretical work was done in the twenties and thirties and 

attempts were made to explore the consequences of the theory experimentally. But it was not 

until the fifties that experimental evidence of the existence of these effects was obtained. The 

fascinating story is taken up again below. 

The final two elements that I want to select in this rapid review of the points at which the 

seeds of the resurgence of optics were sown are the idea of scanning as a method of imaging 

and the idea of imaging with radio-waves. I have failed to come up with a completely definitive 

source for the idea of scanning. It is clearly related to early ideas of moving pictures - the 

zoetrope, etc. But I suspect that the first successful way of converting a picture point-by-point 

into a sequence of signals was probably the Nipkow disc as used in the early television systems. 

Zworykin’s iconoscope and similar devices using electronic scanning and the subsequent development 

of electron optics, which became almost explosive during and after the Second World War, 

must also be labelled as crucial components in the evolutionary process. 

Radar systems began merely as sophisticated range finding and direction finding devices and it 

was relatively late in the Second World War when the PPI (Plan-position indicator) type of radial 

scanning presentation began to provide displays that could reasonably be called images. Practically 

all modern electronic imaging systems - whether the imaging radiation is radio waves, visible 

light, ultrasonic radiation, infra-red or electrons - are direct descendants of these war-time 

displays. 

WHAT ARE THE ELEMENTS OF MODERN OPTICAL RESEARCH THAT OUGHT TO BE 

INFLUENCING PHYSICS COURSES? 

I propose in this section to pick out five general areas of optical research that I think are quite 

important enough - and exciting enough - to be influencing physics courses. In a short article, 

it is obviously impossible even to begin to give a complete account of them. What I hope to do 

is to give a quick sketch of each which will,I hope, at least convey the potential and the flavour 

of the topic. At the end of the article, I have given some suggestions for further reading. I have 

deliberately not made this an exhaustive (and exhausting!) bibliography. One could cite literally 

thousands of articles and papers, even from the last‘ two or three years. The list I have given contains 

books and papers referenced in this article, books that I like, books that give extensive 

bibliographies, items representing a reasonable spread of nationalities and topics and a couple 

of my own books put in as part of an author‘s privilege! The five areas I have chosen certainly 

do not represent all that is going on in optics today; I think, however, that these are the areas 

that are mast likely to be rewarding educationally since they all have some very obvious bearing 

or impact on everyday life. 

Modern views of imaging and diffraction 

Traditional geometrical optics courses approach the whole question of image formation from the 

point of view of rays of light. Even lens designers of, say, thirty years ago, used ray tracing 

through the complete system as the basis of their operations. Nowadays the approach is entirely 

different and, whatever the radiation used, considers the relationships between the distribution 

of amplitude and phase in some one plane of the system with that at some other. In other words, 

the whole pattern is dealt with at once. 

23 1


Figure la. Projector showing both slide and image (on screen A). 

b. Image if the screen is moved to position B. 

c. Image if the screen is moved to position C. 

In all three cases, the information about the slide is present in some form on the screen, although it is only completely intelligible 

with the screen in position A. 

The relationships between these distributions can be described in terms of the concept of 

Fourier Transformation, or through the idea of the transfer function, or in various other ways. 

For our purpose here, however, we wil use a very simple illustration to put over the idea. 

23 2


Consider an ordinary 35 mm slide placed in a projector (figure la). Clearly, one important 

plane is that of the slide and another is that of the screen. It is also obvious that (assuming the 

projector to be a good one) there will be a very close relationship between the intensity distribution 

at the slide and at the screen. But suppose we take any other plane parallel to the slide and 

located anywhere between the slide and the screen (figure 1 b). For every position there will be a 

different distribution - some may not resemble the slide in any way - others may be blurred 

representations of the slide (figure IC). But, if you pause to think about it for a moment, it must 

be obvious that the same information (i.e. all the information relating to the picture on that 

particular slide) must be present in every one of the intermediate planes. Let us go one stage 

further. Suppose we place the slide in the projector but we remove the projector lens (figure 2). 

The distribution of light on the screen wil be a more or less uniform patch of light and yet it 

must again follow that all the information about the slide must be there,(compare with the planes 

between the slide and the lens in figure 1). The patch of light on the screen can properly be 

described as a hologram since every point on the screen contains information about every point 

on the slide. This is not a very useful kind of hologram and we shall see later what we have to do 

to make it into the powerful and exciting device that most people think of in this connection. 

Figure 2. Patch of light on the screen at A with the arrangement as for figure la but with the projector lens removed; again, the 

information about the slide must be present in some form on the screen. 

What have we really established so far in terms of physics? Merely that the first stage in one 

particular image-forming process is that light interacts with the object and all the information 

needed to form the image is encoded in the light. In the second stage, the lens sorts out all this 

information and places it in the appropriate places on the screen to form an image. We may 

describe these two processes as encoding and decoding, as scattering and recombination, as 

diffraction and focusing, or even (loosely) as Fourier transformation and Inverse Fourier transformation. 

23 3


It can be shown that something very like this pair of operations occurs in all image focusing 

systems, whatever the radiation used, be it radar to see through fog, infra-red radiation to see in 

the dark, ultrasonic scanning to see inside the human body, or X-ray crystallography to look at 

atoms. In a moment, we wil pick out just one or two examples to illustrate this theme. But, 

first, let us take a very elementary look at the theoretical aspect. We need to ask the question 

‘If the information is all there in the patch of figure 2, in what form does it exist?’. We shall 

examine first what would happen if the slide were illuminated by parallel, monochromatic waves. 

Figure 3. Path differences for waves scattered from two points A and B for various separations between A and B. In a, the points 

are five wavelengths apart and in moving from P to Q on the screen, the path difference becomes half a wavelength. In b, the 

points are two wavelengths apart and it is necessary to move from P to Q’ in order to make the path difference half a wavelength. 

In c, the points are half a wavelength apart and even at 90’ to the original direction the maximum path difference is clearly half a 

wavelength. 

234


Consider any two points A and B in figure 3a that are rather far apart on the slide used in 

figure 2. At point P on the screen, the waves from A and B wil be in phase since they have 

travelled the same distance. At point Q however there wil be a phase difference corresponding to 

an extra path distance d. Let us suppose that this is just one half wavelength X/2. In figure 3b 

the points A' and B' are much closer together than A and B. Again the waves are in phase at P 

but at Q the path difference d' is very much less than d in figure 3a. In fact we have to move out 

to Q' before the path difference is equal to h/2. In figure 3c the points A'' and B" are considerable 

closer together than one wavelength of the radiation used and so, even if we were able to 

collect all possible waves including those going off in the direction of Q", the path difference 

would be less than one half wavelength. 

Figure 4a. A regular object. b. The scattering path of a in coherent light. c. A restricted portion of b. d. The image formed on 

recombining c. e. Further reduction of b. f: The image formed on recombining e: note particularly that the centre group now 

appears to be 3 x 3 rather than the 5 x 5 of the real object. [22.] 

235


This demonstration suggests to us that the information is encoded in the form of phase differences 

and immediately establishes two important points. First (as in figure 3c) no information 

can be encoded about dimensions much less than a wavelength of the radiation used and so it is 

no use having a superb ‘optical’ system to form an image if the wavelength is too large. Second, 

even if the radiation has been suitably chosen, it is still important to include all the waves from 

the object. For example, if in figure 3b the aperture of the optical system cuts out all the waves 

outside PQ, then the image wil be no better than the image formed in figure 3c with too long a 

wavelength. Figure 4 shows some photographs taken to illustrate what can happen when either 

the wavelength is too long or the aperture is too small. But to return to the patch of figure 2 

again - if there are phase differences, why cannot we see interference fringes? Consider figure 

3a; it is reminiscent of the arrangement for Young’s fringes and, under the right coherence 

conditions, would produce sinusoidal interference fringes on the screen. If we now add all the 

other possible pairs of points on the slide that make up the picture, each pair would produce a 

sinusoidal fringe pattern on the screen. With the experiment as described so far - using an 

ordinary projector - we do not see a pattern because the light is both spatially and temporally 

incoherent. There is in fact a pattern on the screen at any instant - but it is a superposition of 

many patterns because of the spatial extent of the source (lack of spatial coherence) and it is 

changing at an enormous rate with time. If the light used were coherent both temporally and 

spatially - as in our assumption for the theory - then the pattern of interference bands would be 

stationary and visible, as indeed is shown (for the same slide) in figure 5. 

Figure 5. Repeat of the experiment used to produce figure 2, but now the slide is illuminated by light that is temporally and 

spatially coherent (laser source). 

236


Figure 5 is a much more useful sort of hologram since we can now see the result of the superposition 

of all the interference fringes. But notice that if we intend to recombine or focus the 

image with a real lens, then it makes little difference which illumination we use; the lens can deal 

with the actual distributions corresponding to 2 or 5 equally well. It is when we are adopting 

recombination techniques without lenses that the difference becomes really significant. 

Principle of the pinhole 

camera 

Figure 6. The principle of the pin-hole camera. [23.] 

Now let us look briefly at the various ways of recombining or decoding the information from 

the first stage of our image-forming process. 

By far the simplest technique is to use a pin-hole (figure 6). In effect, we are eliminating at 

each point all the information about all the other points. This is clearly extravagant and leads to 

very faint images. There is a well known demonstration in which several pin-holes are used. Each 

then produces a laterally displaced image, but a suitable prism over each can superimpose all the 

images and produce a single brighter one; one then realizes that these prisms are portions of a 

lens. The lens takes the information about any one point on the slide that was to be dispersed to 

all points on the screen and diverts it so that it all arrives at one point. This is the most 

economical way of recombining. 

Figure 7 shows how a lens can be regarded as a means of changing the curvature of the wave 

fronts. Or, in other words, of ensuring that all the optical paths between 0 and 0’ are identical; 

the varying thickness of the lens achieves that end. In this example, the path lengths are identical. 

But if the path lengths differed by whole multiples of a wavelength, the pattern would be the 

same. The zone plate is a device which can produce images as does a lens, but its images involve 

path differences that are various whole numbers of wavelengths and hence a zone plate produces 

more than one image. The zone plate is a fascinating device but we have not time to discuss it 

further in this article. A different example of multiple images from path differences of whole 

numbers of wavelengths occurs if one forms an image in coherent light of a regular mesh - a 

handkerchief for example. A whole series of quite acceptable images of the mesh can be formed 

with the imaging lens at different distances from the mesh. These are sometimes called ‘Fourier 

23 7


Images’; really good multiple images can only be obtained if the coherence is very high and are 

best demonstrated with a laser source. Figure 8 shows examples. 

Figure 7. The lens as a phase adjuster. [23.] 

Figure 8. Multiple or Fourier images: the arrangement is as for figure 1, but with a laser source illuminatlng the slide which is 

now a piece of gauze in a roughly circular hole in a cardboard screen. a is the image at the normal conjugate position at which 

a focused image of an irregular object would be produced. b, c and d are some of the additional ‘images’ that seem to come into 

focus successively as the gauze object is moved away from the lens. The lens-to-screen distance remains fixed. 

23 8


Highly coherent light leads to other imaging possibilities, perhaps the most well known of 

which is that produced by a holographic system. A detailed discussion of holography would be 

out of place, but an idea of the possibility can be obtained by considering figure 5. This is the 

patch produced in coherent light without any lens. Using the principle of reversibility of light 

paths, if we could create a distribution of light corresponding in amplitude and phase to that 

in the patch, then we should be able to produce an image in the position of the original slide. 

It was the phase question together with the difficulty of achieving the necessary high degree of 

coherence that delayed the practical achievement of holography for so long. For very special 

cases, it had already been performed by W.L. Bragg, by H. Lipson and others during the early 

years of the Second World War. The first achievement of holography in the form in which we 

now know it followed only about two years after the invention of the Helium-Neon Laser in 

1960. Leith and Upatnieks in the United States and Denisyuk in the Soviet Union achieved 

practical systems around about the same time. Figure 9a shows a typical arrangement. One of the 

striking and important features of the image produced by holography (often called a reconstructed 

hologram) is that it is three dimensional. In an ideal system, when the holographic plate is placed 

in the laser beam (as in figure 9b), the set of waves generated by .the interaction should be 

identical with those originally produced by the object and hence the eye should be unable to 

distinguish between the real object and €he reconstructed hologram. 

\ 

a 

b 

Figure 9a. Schematic arrangement for producing a hologram. b. Schematic arrangement for reconstructing an image from a 

hologram. [23.] 

But suppose there is no lens available - for example, an X-ray lens is improbable and radio and 

ultrasonic lenses are, to say the least, cumbersome. If the pin-hole (figure 10) is moved until it is 

in very close proximity with the slide, then for any one position of the pinhole the total illumination 

of the screen corresponds to information about one point on the slide. If the pinhole is 

moved about in a systematic way the information about each point can be determined. This 

system is known as scanning and forms the basis of most imaging systems using radiation other 

than visible light or electrons. It has the disadvantage that the information is not available simultaneously 

for all points of the object; but this becomes an advantage khen the information is to 

be transmitted over a single channel such as a telephone or radio link and the distribution of 

information in space is converted into a time-varying distribution which can easily be transmitted. 

239


a 

I 

C 

Figure loa. A pin-hole camera can be changed into a point-by-point scanning system by moving the pin-hole towards the object. 

h. When the pin-hole is in contact with the object, only one point of the object can be studied at once and radiation from it 

covers the whole screen. A photo-cell at C would thus respond to the amount of scattering from P, , P, , P, , etc. as the pin-hole 

is scanned cross the object. If the lamp is moved in synchronism with the pin-hole to L, , L, , L, , etc. and its brightness is controlled 

by the output of C the lamp will produce an image of the object point-by-point. c. The original Nipkow disc used for 

scanning in early television. In this case a spot of light was made to scan across the object: the result is the same as if the pin-hole 

had scanned across in contact with the object. [23.] 

Suppose that the object we are studying is so small that scanning is out of the question, for 

example, if we wish to see the arrangement of individual atoms in - say - a molecule of penicillin. 

We are seeking detail on a scale of about lO-'O m and the only radiations with wavelengths in the 

right region are electrons, X-rays or neutrons. Neither X-rays nor neutrons can be focused by a 

lens and, although electron lenses are well known and commonly used in electron microscopes, 

it turns out that no one has yet produced electron lenses that wil work at an aperture large 

enough to achieve the resolution promised by the wavelength. Recently, electron micrographs 

240


revealing individual atoms under rather special conditions have been achieved, but there is still 

some way to go before useful images are readily available. 

We are thus left with the awkward situation that we can encode information at the right level 

of detail using X-rays, neutrons or electrons, but we cannot focus an image experimentally. Nor 

can we satisfactorily record the phases (as with a hologram) and so we must solve the problem of 

interpreting the encoded pattern (as for example figure 5). The whole history of X-ray diffraction 

from 19 12 to the present date is concerned with finding ways of sorting out the encoded patterns 

without a lens. The success has been almost unbelievable and structures such as large proteins 

have been worked out in detail by these indirect techniques. 

Thus in present-day optics we group together all the various imaging systems together with 

X-ray, electron and neutron diffraction and see them all as aspects of the same basic physical 

principle of encoding and decoding information using radiation as the investigating medium. 

Lasers 

It is clear from the last section that the laser has had an enormous influence on the developments 

in Optics and therefore is worthy of a separate section. 

As with so many discoveries, one can find the seeds in scientific work of a much earlier period. 

Einstein, in fact, as long ago as 19 16 suggested that the phenomenon of stimulated emission of 

radiation should exist but it was not until about forty years later that stimulated emission was 

demonstrated; the first lasers operating in the visible light region appeared in 1960. 

Until the discovery of laser action, there were only three essentially different ways of producing 

electromagnetic radiation. The thermal radiation from hot bodies was one possibility (e.g. 

infra-red sources, tungsten filament lamps, etc). The spontaneous emission of radiation from 

excited atoms or molecules was a second (e.g. sodium or mercury-vapour lamps, characteristic 

X-rays, etc). The radiation produced by the acceleration or deceleration of charges (classically) 

was the third (e.g. radio and micro-wave sources, ‘white’ X-radiation, etc). 

The exploitation of stimulated emission is a remarkable story. The basic idea is simple. An 

atom which is in an excited state with an energy E, can be stimulated to decay to a lower state 

El by the action of a photon of frequency U such that hu = E2 - El . We could write the equation 

for stimulated emission as 

E2 + (hu) +- El i- 2 (ku) 

But the truly remarkable features of the phenomenon are, (a) that the new photon has the same 

frequency as the one causing stimulation, (b) that the new photon’travels in the same direction as 

the original one, (c) that the new photon is in phase with the original one, (d) that the new 

photon has the same polarization as the original one and (e) that the instantaneous rate at which 

the process of production of new photons occurs is proportional to the density of existing 

photons of the same frequency. 

Feature (e) thus means that the process has in-built positive feed-back which results in an 

‘avalanche’ effect; feature (b) means that all the new photons are travelling in the same direction 

and hence the result is enormous power at one single frequency travelling in one single direction. 

The earliest maser (microwave amplification by stimulated emission of radiation) used the two 

lowest energy levels of an ammonia molecule. The first laser (light replaces microwave in the 

acronym) used ruby, which is aluminium oxide with some of the aluminium atoms replaced by 

241


chromium. This laser is operated by irradiating the ruby with a high intensity flash from a xenon 

flash tube. The ruby itself is in the form of a cylindrical rod with polished ends. Some of the 

atoms achieve a metastable level and their decay in the confines of the ‘cavity’ produced by the 

polished parallel end faces leads to the avalanche effect. The energy required to operate the flash 

tube rapidly enough to produce continuous radiation is enormous and so ruby lasers are usually 

used only in a pulsed mode. 

Gas phase lasers using, at first, mixtures of helium and neon, and later many other gases, are 

now well established and continuously operating lasers developing 5 to 10 watts entirely at one 

frequency in the visible region are now made commercially. 

Perhaps the most exciting of recent laser developments is tlie dye laser. Organic molecules 

have a great many possible excited states when one considers all the possible vibrational and 

rotational modes. In fact it turns out that the energy levels become almost continuous distributions. 

In order to act effectively as a laser, the molecules used must absorb very strongly; dye molecules 

have this property to a marked degree. A solution of a dye such as rhodamine wil lase over a 

considerable band of frequencies. If then the beam, after traversing the dye cell, is either diffracted 

by a reflection grating, or dispersed by a prism and a mirror, it is possible to ‘tune’ the laser so 

that it operates at a specific frequency within the band determined by the geometry of the grating 

or prism. 

Before leaving the topic of laser sources, it is important to mention semiconductor lasers 

which, as we shall see in the next section, play a very important role in communication. Imagine 

a p-n junction in which the n-side of the junction is made negative and the p-side positive. As a 

result the free electrons in the n-type material wil be driven towards the junction and, similarly, 

the holes in the p-type material move towards the p-n layer. Under certain conditions, holes and 

electrons can combine in the layer to give a photon of energy corresponding to the energy gap. 

A typical semi-conductor laser might be made of gallium arsenide. The faces of the materials in 

contact might be about I mm square and the actual p-n layer may be only of the order of a 

micron thick. A pair of faces of the junction perpendicular to the junction layer is highly polished 

and the laser action takes place in the layer. A very high current (for the given dimensions, it 

might be as much as 100 A) is passed through the junction and, although continuous action is 

possible, it is usually more convenient to use pulsed operation. For communication purposes - 

especially as nowadays signals are conveyed in pulse-coded form - these tiny devices can be of 

enormous value. 

The fact that laser light is so highly coherent means that many of the techniques that were 

previously possible only at radio or microwave frequencies can now be used at the very much 

higher frequencies of infra-red and visible light. For example the heterodyne principle is widely 

used in radio, and with laser sources it becomes possible with light. For example, if a laser beam 

is reflected back from a mirror on a moving object a doppler shift, occurs in the frequency of the 

returned beam. This ‘beats’ with the original beam to produce a heterodyne signal which can be 

used as a measure of the velocity. 

The non-linear properties of some solid materials can be used to produce interactions or 

modulation between two laser beams. In particular, if a powerful laser beam is passed through 

non-linear material, the output wil contain components of twice the frequency. Hence a frequency 

doubler at visible frequencies is possible. Since laser action becomes increasingly difficult as the 

frequency rises, this provides a valuable source of higher frequency laser light. 

The enormous intensity achievable with continuously operating lasers - quite apart from all 

the other useful properties - has in itself led to a revolution. For example, in my own work on 

optical transforms in the 195Os, we used a high pressure compact mercury arc as source - it was 

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the brightest source available at the time - with multi-layer dielectric interference filters to 

isolate one particular spectral line - usually the green. Typical exposures were measured in 

minutes (between half a minute and twenty minutes was the common range). With even a 1 mW 

laser, the exposures can now be measured in thousandth’s of a second! 

The energy density in a high-intensity laser beam can be so high that the electrical breakdown 

strength of the gas or liquid through which it is travelling may be exceeded and, under the right 

circumstances, this can be used to provide highly condensed plasma regions. Whether the containment 

problem can be solved so that such concentrations could reach the temperature levels 

required for fusion to occur remains to be seen. But the possibility is an exciting one. 

Optical communication 

Fibre optics has made incredible strides since the basic idea was used as a parlour trick a hundred 

years ago. A beam of light was passed horizontally through an empty flask which had a hole in 

the side. When the flask was filled with water the beam of light was trapped in the jet of water 

emerging from the hole and followed a curved path to the floor. An optical fibre is a core of glass 

of high refractive index coated with a sheath of glass of lower refractive index. A typical fibre 

may be 10 microns (10 X low6 m) in diameter, is very flexible and is capable of transmitting light 

over great distances without appreciable loss. An unsheathed fibre wil of course transmit by total 

internal reflection just as effectively, but moisture condensed on the surface, or contact between 

two fibres, etc. will lead to ‘leakage’; the lower refractive index coating minimizes this problem. 

Coherent bundles of fibres - i.e. those in which the relative position of any fibre is the same at 

both ends - may be used for transmitting images and are finding wide use in medical and other 

applications. They are, however, expensive and incoherent bundles in which the emphasis is 

simply on transmitting a quantity of light from one end to the other are very much cheaper. 

The combination of fibre optics transmission and modulated laser sources perhaps provides 

the most exciting of all the many prospects for the future. Even when the necessary protective 

armour is added, optical cables are extremely light compared with copper conductors. But they 

have further advantages that they are not subject to earthing or cross-talk problems; they are 

immune to electromagnetic fields; they are very difficult to ‘tap’ and so lead to improved security 

for the data transmitted; and finally, of course, they have the supreme advantage of involving 

very high frequencies indeed (at 600 nanometres the frequency is 500 million megahertz) and 

hence the bandwidths that can be used are vey much larger than for radio waves. 

The technology of these communications is developing rapidly. For example, a wide range 

of materials other than glass may be used. A single-mode fibre in current use, for example, has 

germanium doped silica (n = 1.471) for the core which is 2.5pm in diameter. The cladding is 

pure silica (n = 1.457) and a thickness of 40pm and hence the overall diameter is 82.5pm. A 

typical 4800-pair copper telephone cable might be about 5 cm in diameter; an optical cable with 

the same equivalent number of pairs would be only about 6 mm in diameter and would also have 

the other features mentioned above - increased bandwidth, greater security, etc. 

Some of the key problems are those of making and breaking connections with minimum light 

loss, the development of suitable light-sources and the design of amplifier systems to act as 

‘repeater’ stations on long links. Tiny semi-conductor lasers may well prove to be the most useful 

for both purposes, especially as many signals nowadays are transmitted in digital or pulsecoded 

form. 

Because fibre optics started from the notion of multiple total internal reflection, the fact that 

optical fibres are really wave guides is sometimes missed. But thinking of them in this way is 

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much more profitable and already transmission in optical fibres is being classified as ‘single mode’ 

‘multi mode’, etc. just as for radio-frequency waveguides. 

Finally, in this brief survey in which we are really concentrating on the optical aspects rather 

than the communication aspects, we should remind ourselves that dispersion occurs in media 

such as glass. Consequently, unless the light used is of a very narrow defined frequency, signal 

pulses may become diffuse because the different frequencies present propagate at different 

velocities. This is one of the reasons why lasers, producing a very narrow frequency band, are an 

important component in optical communication systems. The high intensity is, of course, an 

added bonus. 

Imaging systems 

Perhaps the most familiar imaging system for most people is the television set, and the advent of 

television games and domestic video recorders has brought pieces of highly sophisticated technology 

into people’s homes. Colour television itself is a remarkable feat; the problems of transmitting 

three separate coloured moving images in precise register with each other is a formidable one. 

To record such images on tape or disc and play them back with equipment cheap enough to be 

brought on a domestic scale is a triumph of technology. And the facility for slow motion or still 

picture replay means that a form of image processing is now available relatively cheaply. 

But in order to illustrate the exciting potential of imaging systems in a brief section, I have 

chosen to concentrate on only three topics; electron microscopy, medical imaging and pictures 

from space. 

In its optical essentials, an electron microscope obeys the normal criteria for an image-forming 

system. The radiation is electrons and, if we assume that an accelerating voltage of say 120 kV 

is used, the equivalent wavelength of the electrons will be about 3 picometres; that is, of the 

order of 1/100 of the spacing between atoms in solid matter. In principle, therefore, the electron 

microscope should be able to image atomic locations quite clearly; all the information could be 

satisfactorily coded. However, you wil recall that we pointed out (p. 000) a second limitation on 

resolution, namely that all the information encoded in the radiation might not enter the 

recombination section of the system. This is exactly what happens with electron microscopes; 

the electron lenses can only be made with very tiny apertures and, in practice, really complete 

resolution of atoms in all forms of material remains out of reach. In certain very special cases, it 

can be done. 

The other major problem in electron microscopy was that of achieving a large depth of field 

when focusing. The scanning electron microscopes - in which the electron optical system is used 

to produce a very fine beam of electrons which scan the object and, after scattering, are collected 

by a counting device from which the signals are presented on atelevision type display - deal 

with this problem and, incidentally, produce some of the most attractive and exciting pictures 

in the process. 

In electron microscopes, just as with optical microscopes, it is important to remember the 

Abbe principle. That is that the final image is not necessarily an image of the object. It is in fact 

an image of such an object as would give a scattering or diffraction pattern corresponding to that 

portion of the pattern of the real object that enters the system. An obvious example would be an 

attempt to image a diffraction grating whose transmission function was a square wave. Its scattering 

pattern would be a series of regularly spaced orders of diffraction; but if only one order on 

each side of the centre entered the recombination system, the image could only be a sinusoidal 

distribution of the same period as the square wave. False images are all too easy to obtain if care 

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is not taken, and one must always remember the dictum that, when we focus, we make the object 

look as we think it ought to look - which is not necessarily as it really looks. 

Now let us turn for a few moments to medical imaging. The developments since the early days 

of the simple ‘shadow’ radiograph are enormous. I shall pick just three to illustrate the point. The 

first is the use of ultrasonics. The advantage is that the waves do not themselves cause any tissue 

damage and so can be used safely, for example, during pregnancy. The object is scanned with 

a beam of ultrasonic radiation and the scattered radiation is detected with a suitable transducer 

and an image is built up on a television picture tube. The various boundaries between bone, soft 

tissue, fluids, etc. show up clearly and, for example, it is possible.to see the outline of many 

organs within the body. The detection of multiple pregnancies is particularly easy as the foetal 

skulls can be recognized clearly within the amniotic fluid. 

Infra-red imaging - or thermography as it is often called - provides an example of an imaging 

system in which the object is self luminous. The human body radiates in the infra-red region and 

the nature and intensity of the radiation depends largely on the surface temperature. It is well 

known that changes in the surface temperature of the body may be symptoms of abnormalities 

such as, for example, malignant growths. Infra-red scanning devices which lead to the production 

of a map of isotherms for the body, or part of it, can therefore help in the diagnosis of various 

disorders. 

One of the most recent and perhaps most revolutionary imaging systems is the computer 

tomograph. A series of X-ray beams is used to produce radiographs through a particular section 

of the body in a considerable number of directions. The resulting pictures are stored in digital 

form and a computer program processes the information in such a way that it is re-assembled to 

give a sectional view of the part of the body being considered. The effect is just as though the 

body had been sawn through and then the section photographed. The results are not only dramatic 

but extremely valuable as a diagnostic tool. A much simplified demonstration of the principle of 

the tomographic imaging system is given in Images [ 71 . 

Finally, we shall consider just two of the problems of the transmission of images back from 

space probes as examples of an application of image-processing. The first is relatively straightforward 

and involves removing the raster from television images so that they are more acceptable 

as pictures. The image can be thought of as the product of two intensity distribution functions. 

The first is the picture required; the second is the function representing the stripes. If a transparency 

made from the television image is placed in an optical diffraction apparatus (i.e. we 

explore the first stage of the formation of an image of it in coherent light), its diffraction pattern 

wil be related to the diffraction patterns of the two functions. The diffraction pattern of the 

‘stripe function’ is merely that of a diffraction grating - i.e. a set of regularly spaced points on 

either side of the central beam. Fourier transform theory tells us that the multiplication of two 

functions in one of the related Fourier planes corresponds to convolution in the other. In the 

diffraction pattern of the product, therefore, the pattern corresponding to the picture required 

is convoluted with (i.e. distributed to each point of) the set of diffraction grating peaks. All 

information about the picture therefore exists at each of these diffraction peaks. So, if we 

filter by eliminating all but one peak, and then recombine the image, the stripe information has 

been eliminated and we have an unstriped picture (see figure 11). This is an example of what one 

might call ‘cosmetic’ filtering. Clearly no information can be revealed about any detail of the 

picture that happens to be in a ‘dark’ stripe. However, if the object being imaged is static and the 

raster is made to move about relative to it, the resulting pictures can be integrated into a more 

useful whole. In considering whether a filtered image is likely to reveal additional detail, rather 

than merely looking more attractive, it is important to consider the operation from an information 

standpoint. If the process enables us to transform more information, then the chances are the 

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Figure lla. Object made up of transparent and opaque regions. b. Centre region of the diffraction pattern of a showing only 

three repeats in the vertical direction; in the full pattern there are several more repeats above and below those shown. C. Central 

unit of b. d. Recombination of c. [24.] 

result wil be more meaningful; if, on the other hand, no additional information is incorporated, 

then the filtering is merely cosmetic. 

The second problem that we shall consider illustrates this difference very well. Noise is the 

great enemy of communication and it may often happen when, for example, a space probe working 

at extreme range, or with almost exhausted power supplies, that a visual signal is completely 

obliterated by the ‘snowstorm’ effect. However if we are trying to transmit a picture that is 

stationary for a given length of time, it may be possible to filter out the noise. The possibility 

rests on the randomness of the noise signal and the relative constancy of the required visual 

signal. There are many ways of using this information. One possibility would be to convert the 

sequence of frames into digital form and then to integrate all the successive digits corresponding 

to each point of the image in turn. If the integration is carried out over a large enough series of 

frames the ‘noise’ wil average out and the required signal wil be enhanced. 

Image processing generally is a most useful and valuable technique. But it can also be misleading 

and it is very important that the user should know exactly what has been done to a particular 

246


image ifmis-interpretation is to be avoided. (In figure 4 we saw that the restriction of the aperture 

could lead to a complete misinterpretation of the number of holes in the central section.) 

The importance of the human element 

We see the world around us by using the eye-brain system, and it has always amazed me that so 

often physics students wil learn about the eye as an optical system but will not be led to appreciate 

the real significance of its being attached to a brain. Optical illusions are not merely curiosities 

with which to amaze and confound your friends; they are very important pointers to the way 

in which we respond to our surroundings and to the limitations that our human characteristics 

impose. This section merits a whole book to itself and I can only pick out one or two examples 

to illustrate the kind of thing I have in mind. 

Most physicists are quite familiar with the idea of three-colour vision. Colour television is a 

permanent reminder to us of its practical application. But colour is a very subjective phenomenon 

and our judgement about a colour depends on circumstances, on the nature of the illumination, 

on the surroundings of the colour observed and on many other factors. For example, a piece of 

uniformly dyed yellow cloth which is held loosely so that it falls into folds wil be recognized 

by any viewer as being of uniform colour. But if invited to look again - for example with the 

eye of a painter about to paint a picture of the cloth - the viewer will realize that the retinal 

image of the cloth will be made up of an enormous number of different shades of yellow. What a 

remarkable process is performed by the brain in noting all these variations, in recognizing that 

they fit together in a way that corresponds to the incidence of light on the cloth and to a valid 

system of folds and hence deducing that the colour is in fact uniform. One of my favourite 

illusions involves a large sheet of card of uniform colour - grey is useful - which is covered 

entirely by another card with two square holes in it so that the viewer sees two square patches 

of grey separated from each other. The upper card is divided into halves and each half coloured 

uniformly with a different colour, for example, yellow and blue. The viewer thus sees each patch 

of grey surrounded by a different colour and it is difficult to believe that the two patches are 

indeed the same grey. The effect of the surroundings in determining the colour is very powerful. 

Finally in discussing colour we might mention an effect that sometimes baffles amateur 

photographers. Suppose a close-up portrait is being taken; the photographer wil carefully choose 

the background, but very often wil ignore surroundings that are outside the field of view. But if, 

for example, there is a red brick wall at one side of the subject, a warm red glow may be reflected 

on to the face. In the live situation, as the photograph is taken, the glow is ignored because the 

eye-brain system sees the wall and makes suitable compensation; but when the colour photograph 

is printed the photographer cannot understand why the subject has such a red face. 

We take very much for granted the ideas of perspective and happily draw pictures using the 

principle that parallel lines (roads, edges of buildings, etc) wil meet at a point on the horizon. 

But how often do we realize that a considerable amount of brain processing is involved in 

recognizing that the lines on a flat piece of paper represent a three-dimensional object. Professor 

Richard Gregory tells of a blind acquaintance of his who, as a result of an operation, had his 

sight restored in later life. This man was unable to appreciate many of the common optical 

illusions and had to learn from scratch how to relate images on the retina with three-dimensional 

objects in the surrounding world. 

Finally, in this very brief section it is worth reminding physicists from time to time that we 

have a built in tendency to see what we want to see. Most people wil have had the experience 

of reading an article in which there are misprints and, if the article is sufficiently absorbing, not 

noticing the errors. Another reader perhaps less interested in the topic wil spot the errrors 

instantly . 

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ISN'T ALL THIS TOO COMPLICATED AND EXPENSIVE FOR SCHOOLS? 

It was not part of my brief to give an outline syllabus or to suggest how a course in optics might 

be planned. On the contrary, the aim of this article was to try to convey something of the excitement 

of modern optics and of its importance in the forefront of physics research in the hope of 

persuading those much more knowledgeable than I about school physics that the time is ripe for 

optics to be regained as a significant part of the school syllabus. 

But before leaving the topic it would seem reasonable to try to answer the possible arguments 

that might be cited against optics, in particular, the view that the topics I have discussed might 

be regarded as too expensive or too complicated to be treated at school. I do not think this is the 

case at all. I have spent a good part of my professional career developing methods of researching 

and teaching in X-ray diffraction which circumvent the very complex mathematics that can be 

involved. Optical analogue methods (see, for example, the Atlas of Optical Transforms 181 ) have 

excited a great deal of interest simply because they do provide a relatively speedy visual way of 

introducing the potential of X-ray diffraction to non-physicists without mathematics. And a large 

part of the secret of their success is that they are visual. It is well known that diagrams and 

photographs add enormously to the ease with which a difficult idea can be transmitted to listeners 

or readers and, clearly, optics is the subject without equal for visual presentation. 

A good deal of the teaching can be done with slides and photographs and they are certainly 

not beyond the reach of schools. Lasers (%mW helium-neon) are now down in price to a level 

that should enable a school to have one and the rewards are really considerable. There are several 

bits of apparatus centred round a small laser now available. Image processing, for example, is easy 

to demonstrate cheaply (e.g. Taylor [9]>. But we must not forget that Newton and Young and 

others did experiments with simple pinholes, slits and prisms using sunlight and there is no 

reason why this should not be repeated. Diffraction is easy to demonstrate by viewing a sodium 

street light through an umbrella. Off-cuts of 1 cm thick plate glass as used for shop windows can 

be acquired very cheaply from glaziers and are an excellent substitute for optical flats. My 

earliest recollection of being fascinated by images was in accidentally seeing a pinhole image of 

the world outside a cellar being used as a photographic darkroom. I suspect that this may be one 

of the important clues to the re-introduction of optics as an exciting subject at school level. 

Let us go beyond the old-fashioned ideas of image-seeking using pins, geometrical ray-tracing, 

parallel-lined diffraction gratings, etc. and remember that optics is concerned with images of the 

real, colourful world outside. I think the challenge of developing a course of school optics that is 

exciting, is appealing to students who are not heading for science careers and which can give all 

students a feeling for the relationships between science and everyday life is one that should be 

taken up. I hope that perhaps this article' might encourage those who are already thinking along 

these lines and perhaps even convert someone who has not yet begun. The resources available are 

enormous and the likely rewards in terms of creating a genuine interest in physics and its relationships 

to the world around us seem to me to be very considerable indeed. 

REFERENCES 

1. HousTOUN, R.A. A Treatise on Light. 1st ed. London, Longmans & Co., 1915. 

2. ROBERTSON, J.K. Introduction to Physical Optics. 1st ed. New York, D. Van Nostrand Co., 1929. 

3. NEWTON, Sir Isaac. 1704. Upticks. New York, Dover Publications, reprinted 1952. 

1. I a m most grateful to Dr. G. Harburn for his helpful comments and criticisms on this paper. 

248


4. HUYGENS, C. Traiti de la lumikre. 1st ed. Leiden, 1690. (Rendered into English by Silvanus P. Thompson, 

Treatise on Light, London, Macmillan & Co., 1912.) 

5. ABBE, E. Beitrage zur Theorie des Mikroskops. .. Archiv. fur Mik. Anat., Vol. 9, 413, 1873. English translation 

by H.E. Fripp, Proc. Brit. Nut. Soc., Vol. 1,200, 1875. 

6. PORTER, A.B. On the Diffraction Theory of Microscopic Vision. Phil. Mag., Vol. 11, 154, 1906. 

7. TAYLOR, C.A. Images. London, Wykeham, 1978. 

8. HARBURN, G.; TAYLOR, C.A.; WELBERRY, T.R. Atlas of Optical Transforms. London, Bell & Hyman, 1975. 

9. TAYLOR, C.A. Unified Approach to Diffraction and Image Formation. Proceedings of GIREP Conference 

on Physics Teaching, Balaban, 1980. 

10. EHLERS, J. et al. (eds.) Imaging Processes and Coherence in Physics. New York, Springer-Verlag, 1979. 

(Lecture Notes in Physics Series, 112.) 

11. FRAN~ON, M. Optique; formation et traitement des images. Paris, Masson, 1972. 

12. JONES, B. et al. Images and Information. Milton Keynes, Open University, 1977. 

13. KALLARD, T. Exploring Laser Light. New York, Optosonic Press, 1977. 

14. KAPANY, N.S.; BURKE, J.J. (eds.). Optical Waveguides. London, Academic Press, 1972. 

15. Laser and Light; Readings from Scientific American. San Francisco, Calif., W.H. Freeman, 1969. 

16. McLEAN, T.P.; SCHAGEN, P. (eds.). Electronic Imaging. London, Academic Press, 1979. 

17. OSTROVSKY, Y.I.; BUTOSOV, M.M.; OSTROVSKOYA, G.V. Interferometry by Holography. New York, 

Springer-Verlag, 1980. (Springer Series in Optical Sciences, 20.) 

18. PARRENT, G.B.; THOMPSON, B.J. Physical Optics Notebook. Society of Photo-Optical Instrumentation 

Engineers, 1969. 

19. PIRENNE, M.H. Optics, Painting and Photography. New York, Cambridge University Press, 1970. 

20. READ, F.H. Electromagnetic Radiation. New York, John Wiley & Sons, 1980. 

21. WRIGHT, G.; FOXCROFT, G.E. Elementary Experiments with Lasers. London, Wykeham, 1973. 

22. Reproduced by permission of Messrs. Bell and Hyman from TAYLOR, C.A.; LIPSON, H. Optical Transfonns. 

London, G. Bell & Sons, 1964. 

23. Reproduced by permission from TAYLOR, C.A. Images. London, Taylor and Francis, 1978. 

24. Reproduced by permission of Messrs. Bell and Hyman from HARBURN, G.; TAYLOR, C.A.; 

Atlas of Optical Transforms. London, G. Bell & Sons, 1975. 

WELBERRY, T.R. 

249

Part IV 

Teacher Education

A case study of science teacher education for a new 

educational system 

J.M. YAKUBU. 

Teacher education: a case study 

The Takoradi Workshop on Science Education (April 1970) was a revolution in the history of 

science education in Ghana. The Workshop, which was attended mainly by practising teachers, 

not only surveyed science teaching in the country but also outlined the aim and objectives of 

science education at all levels and constructed relevant syllabuses. 

The teaching of hygiene, nature study ahd gardening in the elementary schools, which had 

yielded satisfactory results in the Ghanaian society in the 1920s, had degenerated into note 

taking and rote learning. By the mid-fifties, general dissatisfaction with the teaching of science in 

the elementary school was mounting. The Ministry of Education was becoming anxious about 

the state of affairs and, in collaboration with the British Council and the Ghana Association of 

Science Teachers (GAST), carried out pilot studies, organized courses for training college tutors 

and developed syllabuses and encouraged their use. By 1967, full-time personnel, equipment, 

books, finance and bursaries for the training of Ghanaian staff were received from the British 

Council, Unesco and the Education Development Centre (EDC). The Science Unit of the Ministry 

of Education was established to care for science teaching in the elementary schools. Through the 

efforts of the Science Unit, primary school science teaching began to be based on the materials 

produced by the African Primary Science Programme (APSP). Concern was being shown over the 

science knowledge of a pupil whose education ends at elementary level. 

Training-college science reflected what had been taught in the elementary schools - Hygiene, 

Nature Study and Gardening. Science courses in the colleges consisted of Health Science, Nature 

Study, Biology and Rural Science. From 1955 to 1962, the Science Education Unit of the 

Institute of Education, University of Ghana at Legon, and GAST worked closely with the Science 

Panel of the National Teacher Training Council (NTTC) to improve science teaching in the 

colleges. A training college sub-committee was appointed in 1963. It was resolved that the 

introductory science syllabus used for years 1 and 2 in the secondary schools should be adopted 

for years 1 and 2 in training colleges. A new syllabus was to be drafted for years 3 and 4. This 

was to include topics such as Further Properties of Matter, Domestic Electricity, A Biological 

Study of the Environment - Man’s use of Nature, Materials, Continuity of Life and Energy as a 

Wave form. By 1965, the British Council and the NTCC Science Panel collaborated to publish 

the teaching notes for the introductory science course and later for the syllabus for years 3 and 4. 

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By 1968, the GAST Teacher Thining Sub-committee began to call for a change in science 

teacher education. ‘The general opinion expressed was that the development of the right attitude 

to science teaching at the elementary level was more important than teaching of science content 

to the prospective teachers’ [ 1, p. 241. The NTCC Science Panel was to see that this opinion was 

implemented by ‘instituting special science methods, in the Training Colleges’ [ 1, p. 241. It 

became a general view that ‘the training college science course needed general revision to bring 

it into line with current thinking in science education; making it an activity-orientated programme, 

stressing the right attitude to change and ensuring a proper integration of the whole programme 

of science education’ [ 1, p. 241. Unesco was requested to help organize a workshop to discuss 

these issues in detail. 

The history of secondary school science is slightly different. Science teaching was based on the 

syllabus of the British University of Cambridge Local Examinations Syndicate which examined 

students at this level up to the 1960s. In the early 1960s, GAST Science Panels wrote syllabuses 

for the West African Examinations Council (WAEC) which took over the examination of cience 

subjects at the ‘0’(ordinary) level of the General Certificate of Education (GCE) in 1960. 

Interest in Integrated Science teaching was also developing. By 1966, it was government 

policy that all pupils should be taught General Science up to School Certificate Level. A government 

review of the education system of Ghana in 1967 recommended that much greater benefit 

is to be derived from the study, at this level, of science as an integrated whole, composed of 

interdependent parts, than from the study of one or more of these parts in isolation. At GAST 

meetings Integrated Science was discussed with enthusiasm. A unanimous agreement on introducing 

Integrated Science in the lower forms was arrived at, but opinion was divided as to 

whether it should be taught at the upper levels. Dissatisfaction with the teaching of science at 

‘0’ level was revealed - it did not help pupils to develop critical thinking nor was the science 

relevant to the society in which the pupils lived. A curriculum committee was accordingly set up 

to revise ‘0’ level syllabuses and to formulate aims and objectives for science teaching so that 

decisions could be made on the form, content and the approach of the course. These aims and 

objectives were circulated to science teachers and their reactions asked for. Whilst it was a general 

opinion that integrated science should be introduced in the early years, about half the respondents 

also advocated the teaching of Integrated Science in the upper classes. The problem foreseen, 

of course, was the lack of teachers trained to teach Integrated Science. 

Thus the three inter-related strands in science education in Ghana, namely elementary, teacher 

training college and secondary science teaching, had experienced a growing trend of discontent 

with the existing state of science teaching. The meeting point of these strands was the Takoradi 

Workshop. The events, described above, prepared the ground for a revolution in thinking about 

the nature of science and in the attitude to science teaching in Ghana. 

The Takoradi Workshop identified two problem areas which needed action: (a) the content 

of science and the image of science as portrayed by teaching which was irrelevant to the situation 

of the pupils; and (b) the teacher’s attitude to the teaching of science. 

The following recommendations were accordingly made: 

1. Publicity and Public Support. Communication was to be established between Science 

Educators and members of the Ghanaian community. Reports of the Workshop were to be sent 

to policy makers, GAST members, heads of educational institutions, voluntary agents and 

scientists, and feed-back was expected. Science education was thus portrayed as a social activity 

which is the responsibility of the entire community. Science is neither learnt nor taught in a 

vacuum. 

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2. A permanent steering committee was to be set up to see that the decisions of the workshop 

were implemented. 

3. A full-time organizer, preferably Ghanaian, should be appointed to give direction to 

curriculum development work. 

4. Writing teams were to be organized to produce course materials for schools and colleges. 

5. Evaluation teams should be set up for elementary schools, training colleges and secondary 

schools. These teams were to make formative evaluations of courses, train teachers on testing, 

recommend to WAEC appropriate forms and approaches for training college and ‘0’ level 

examinations, develop special evaluation techniques for elementary schools and training colleges, 

and investigate selection procedures. 

6. The pre-service education of graduate teachers was to be entrusted to the University of 

Cape Coast. In-service training with emphasis on content and approach was to be organized and a 

team was to design a programme for such courses. This work culminated in the science specialist 

courses to be described later. 

7. For the Integrated Science at ‘0’ level to be accepted as a qualification for the sixth form 

work, the Ministry of Education and WAEC should be committed to sanction ‘0’ level Integrated 

Science as a qualification for Advanced (A) level courses. 

8. Funds were to be sought for writing and evaluation teams, meetings, training courses for 

teachers, publication of drafts and other materials, expenses of the Steering Committee, publicity 

among teachers and other concerned groups, and for the salary of full-time personnel. 

Since an investigation into the fate of the recommendations is not the purpose of this paper, 

it wil suffice to say that few of the recommendations have been implemented; nor has there been 

any follow-up to the Takoradi Workshop. 

Nevertheless, an important consequence of this Workshop has been an increasing effort by 

teachers and curriculum workers to design materials for science teaching. The Project for Science 

Integration (PSI) is one such effort. Another outcome of the Workshop was the specialist science 

course for teachers started in September 1973. This was a two-year course for experienced 

elementary school teachers (Certificate ‘A’ Teachers), training either to teach science in the 

elementary schools or to organize the teaching of science in a number of schools. After two years’ 

operation, this specialist science course was discontinued in favour of a three-year post-secondary 

training course. 

I have been involved in the training of both the two-year specialist and three-year ‘quasispecialist’ 

course. Writing as a participant observer, my objective in this paper is to try to portray 

the three-year ‘quasi-specialist’ course as it has been, the problems leading to its being phased out, 

then to discuss why the two-year and three-year courses have been said to be failures, and finally 

attempt to postulate what factors should be kept in mind when teachers have to be trained for a 

new educational system, especially in a developing country. But first, it will be necessary to give 

an outline of the Ghana education system, and then proceed on to discuss the structure of the 

course with its attendant problems. 

THE GHANA EDUCATIONAL SYSTEM 

In Ghana, pre-university education is divided into three cycles, all centrally controlled. 

The first cycle is elementary. It comprises six years of primary schooling beginning at 6 years, 

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followed by middle schooling, leaving at 16 years of age. First cycle education is fee-free but not 

compulsory. 

The second cycle consists of secondary grammar, business, teacher, nursing, veterinary, 

agricultural, technical and vocational education. The grammar school takes five years leading to 

the GCE ‘0’ level examination, followed by two years leading to the ‘A’ level for those who 

qualify. Admission into the grammar school is by selection from Primary Six and any of the four 

classes in the Middle School. Each class in the secondary school is heterogeneous age-wise. Education 

at this level is not compulsory and tuition is free. Two types of training college exist: the 

four-year post-elementary and the three-year post-secondary (formerly two years). 

The third cycle comprises the Universities and Diploma-awarding institutions. A new education 

system was due to start operating in September I980 but owing to national economic problems, 

this has been suspended indefinitely. In this system, the first cycle wil be six years primary 

schooling followed by three years of Junior Secondary education. This wil be fee-free and 

compulsory and wil embrace the age range 6 to 15 years. The second cycle wil be two years of 

Senior Secondary (GCE ‘0’ level) followed by two years of Upper Senior Secondary (GCE ‘A’ 

level). The third cycle has not changed very much. 

The Junior Secondary School is the new feature in the system. It was designed to be joborientated 

and at the same time provide background for future development. A core of subjects 

consisting of a Ghanaian Language, English, French, Social and Cultural Studies, Science, Mathematics, 

Agricultural Science and Home Science has to be studied. In addition to this core, two 

subjects from a list of options made up of carpentry, masonry, tailoring, metal work, dressmaking, 

commercial studies, fishing, etc. have to be chosen. Some ninety trial Junior Secondary Schools 

have already been started. The rate at which these schools have been formed has come almost to 

a halt for lack of such resources as books and equipment - a consequence of the economic 

situation. 

Headmasters of the existing secondary schools seem to dislike the Junior Secondary School 

idea. It is claimed that pupils who complete the three-year Junior Secondary are much lower in 

standard academically than those in the third year in the secondary school, but, vocation-wise, 

the Junior Secondary products are superior. It is said that headmasters of secondary schools have 

refused to admit the Junior Secondary products into the 4th year (Form 4) of their schools 

to prepare for the GCE ‘0’ level examination but are admitting them into the 3rd year. At a 

meeting of headmasters in the Northern and Upper Regions, a headmaster was reported to have 

appealed to the government to cancel the Junior Secondary School programme. It wil be recalled 

that the Junior Secondary Schools recruit their pupils from the Primary 6 class without the 

benefit of any selection examination, while the secondary schools select their pupils from 

Primary 6 and any of the four classes in the Middle School through a selection examination. 

Admission into the Junior Secondary School is by interview of Primary 6 children. The headmasters 

argue that because the selection examination into the senior secondary school is more 

difficult than the interview, children with a wider range of ability enter the Junior Secondary 

Schools. Their perfmmance at their final examinations is poor. Rote-learning is dominant and 

they are ignorant of the application of simple scientific concepts. 

It should also be noted that when the Junior Secondary Schools start functioning well,the 

population of the secondary schools wil reduce. One is prompted to wonder whether the 

secondary school headmasters are threatened by the appearance of the Junior Secondary School. 

The Junior Secondary School deserves closer study. 

The three-year post-secondary teacher training course has the task of training teachers for the 

Junior Secondary School. The training of such teachers was started in September 1975 and is 

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already phasing out at the end of the 1980/8 1 academic year. The reasons for phasing out this 

course are that: (i) the rate at which teachers are being produced each year (about 1000) is 

greater than the rate at which Junior Secondary Schools are opened; (ii) since the government is 

not under pressure to open more Junior Secondary Schools the present number of teachers is 

thought to be adequate; (iii) the standard of the teachers produced by this programme is said to 

be much lower than expected; (iv) lack of equipment, materials and qualified staff coupled with 

the difficulty of recruiting the right number of qualified candidates for admission into the 

colleges; and (v) the products from the three-year Post-Secondary Colleges consider themselves 

as specialists, demand preferential treatment and wil not consider postings to the elementary 

schools. 

THE STRUCTURE OF THE THREE-YEAR POST-SECONDARY SCIENCE COURSE 

As mentioned above, a feature of this new course which distinguishes it from the former twoyear 

course is that a degree of specialization in subject areas is combined with initial training. 

Specialist subjects are divided into three groups: Group 1 - Science, Mathematics and Agricultural 

Science; Group 2 - Social Studies, French, Physical Education; Group 3 - Home Science, 

Commercial Studies, Music and Art. Colleges have to choose which groups of courses they 

wish to run. My own College, Bagabaga Training College, runs Group 1 and 3 courses. The Group 

1 course has the following structure: 

Specialist subject 

This aims to provide the student teacher with a basic knowledge of science, mathematics and 

agricultural science up to the GCE ‘A’ level standard. It was the intention to give the same 

weight to all the subjects - and to offer a fully integrated science component. However, it has 

been found very difficult to teach integrated science to ‘0’ level and beyond. And the situation 

is made especially difficult since the three subjects are taught in three departments, each exercising 

jealous control over its own syllabus with hardly any co-ordination among them. 

The NTTC questionnaire to all Principals of colleges involved in this course in 1976 and the 

subsequent analysis of its findings, revealed that, among other things, subject combinations were 

thought to be unrealistic for teacher training. Principals recommended that specialization should 

be deferred to post-initial training. The result of this was that the number of subjects was reduced 

from three to two. 

Project Work 

Every student is required to undertake a project and work at it throughout the three years. The 

topics chosen should be based on an activity in the community and should be of scientific 

interest. Topics such as soap making, vegetable oil extraction, metal work, brewing and herbal 

medicine making have been chosen in the past. The processes and concepts embedded in the 

activities are observed in the local situation and then tried in the laboratory. 

Problems connected with project work are: (i) determining how far the student should go; 

(ii) inadequacy of such resources as library facilities; (iii) the provision of effective guidance to 

the students. Because the aims, objectives and methods of working on their projects have not 

been made clear, students find the project work very confusing and often regard it as a waste of 

time. Not only do they have to be told to look for problems, but they need to be guided on how 

to locate such problems and how to collect and interpret data. 

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Students also find that money is needed in the search for data and, as they are not paid allowances, 

they find the project work a burden rather than an exciting activity. 

These problems could be overcome by stream-lining the format of the Project Work and fixing 

its length. Before embarking on their projects, students should be briefed on how to select their 

topics and how to start. To alleviate the problem of lack of reference books, the Ghana Library 

Board could run a Book Service Scheme whereby boxes of books are lent to a college for a period 

of time. Foreign embassies or organizations such as the British Council could be contacted to 

help with the borrowing of books or even purchasing them from outside the country. To show 

that importance is attached to the project work, a small grant could be given to the students to 

enable them to conduct their investigations properly. 

Advice is assumed to be given by the tutor but, because most of the tutors involved in the 

course have been inadequately briefed on its philosophy, the enthusiasm with which supervision 

was undertaken in the initial stages of the course seems now to have waned. The employment of 

part-time tutors and national service men who are not initiated into the philosophy of the course 

makes it almost impossible to achieve the objectives which the project work was meant to achieve. 

Science Teaching Methods 

Who teaches the methods? 

Science teaching methods are taught by the science tutors and not by the Education Tutor (who 

used to be called the ‘Methods Tutor’). No specific methods have been laid down for this work; 

indeed, all that is mentioned in the syllabus is that activity methods should be used. It has been 

suggested that tutors should teach the syllabus content to the students in the way they expect 

the latter to teach their pupils in the Junior Secondary School. In other words, there should be 

no separate consideration of science teaching methods. The tutor becomes the model. Tutors 

are divided on this issue. While some are in favour of this approach, others think that it is difficult 

to use methods meant for pupils to teach adults. Also, using the tutor as a model kills creativity 

in the student teachers who are expected to be innovative. Some think it preferable to use the 

primary school syllabus as a basis for helping students to make lesson plans and to illustrate 

certain methods of teaching such as guided-discovery methods. This problem is yet to be resolved. 

The idea of the science tutor teaching both the content and the methods of teaching is beginning 

to be unrealistic, especially when part-time tutors who are only interested in the content are 

employed. 

Classroom Experiences 

Since there are no curriculum materials specially designed for the course, we use the primary 

school science syllabus and APSP units. 

Peer group teaching is used. One student prepares a lesson and teaches a small group of his 

colleagues. Then they discuss his method of approach. The tutor visits each group, listening and 

making a few comments. A general discussion on the teaching carried out is then held. 

In addition to their own practice school, most colleges have adopted elementary schools in 

their vicinity for classroom experience. Both students and tutors go to these schools to practise 

the teaching of specific topics discussed in class while others go individually to try apparatus 

that has been constructed or to observe the methods used by practising teachers. In the group 

practice, one student prepares a lesson and teaches it to a class while some of his/her colleagues 

observe. Discussions after these practices have been useful in the sense that the students become 

258


more critical and observant of their colleagues and of their tutors as well. They learn to listen 

to others’ points of view, to criticize wisely and to receive criticism in good faith. Students do 

not panic so much during the later formal teaching practice. The tutor’s roles have become those 

of a motivator and a facilitator. He goes from school to school and from class to class to help 

with problems that may arise; he does not assess the students. 

A questionnaire to past students of this course has shown that the students learnt a lot from 

such classroom experience. They especially enjoyed team teaching. Unfortunately, although the 

method was possible with the two-year students specializing in one subject, it proved to be 

impossible with the three-year ‘quasi-specialist’ students following three un-coordinated subjects. 

The time tables were too tight and there was no allowance for a breathing-space. 

Tra d 1 t i on a I t eac h I n g pr ac t i c e su pervi s I on 

TUTOR 

STUDENT 

TEACHER 

MATERIALS 

Modern teachlng practlce supervision 

- + 

STUDENT 

, ,JENT 

I TEACHER iEACHER h 

\ 

MATER IALS 

A 

I 

+ 

CHILDREN 

Teaching Practice: Supervision and Assessment 

The students have ten weeks of formal teaching practice spread over the three years. Assessment 

of the practice counts towards the final grading of the students. 

Our Teaching Practice supervision is different from the traditional one in which the tutor sits 

at the back of the class. In our course, there is a change in the role of the tutor. He goes round 

from time to time and interacts with the student, pupils and materials. He can help the student 

explain a concept to a pupil or help the pupil perform an activity. In this case, he can appreciate 

the student’s difficulties as well as those of the children. Not only does his relationship with 

the student improve but his own methods are enriched. The supervisor’s role changes from that 

of a stern judge and stranger to that of motivator, facilitator, friend and fellow participant. 

The science tutors in some colleges have been in conflict with the non-science tutors over the 

supervision of science student teachers and the relation between the two groups has become 

strained. While the science tutors believe that one needs to have knowledge of science before 

supervising a science lesson, non-science tutors think that it is not necessary to have any 

knowledge of the subject the student is teaching. They assert that methods have little to do with 

content. The ‘Methods Tutor’ (who is a member of the Education Department) thinks that he is 

259


out of business. In some colleges, a compromise has been reached which allows non-science 

tutors to supervise but requires their gradings and comments to be vetted by the head of the 

science department. In some colleges these tutors are provided with guidelines to help them. 

Brief observation sheets constructed by tutors running the course are used by the supervisors. 

Construction of simple teaching aids from local materials 

The philosophy of the course encourages self-reliance. As far as possible local materials should 

be used in teaching science. Students are therefore encouraged to make science equipment from 

local and waste materials. Workshop practice appears on the timetable. 

Improvisation is especially difficult to practice during times of economic hardship. Empty 

bottles, tin cans and jam jars are hard to come by because canned foods and other foreign 

commodities are scarce on the market. Where empty bottles and tin cans are found, they are 

sold and so improvisation has become expensive. 

The other problem with improvisation is the difficulty of getting tools for carpentry and metal 

work. Not many colleges have woodwork and metal work departments to help. The tutor’s lack 

of knowledge in woodwork and/or metal woi-k is a constraint, but not a serious one since there is 

always a student who can help. 

In spite of these problems, the students enjoy the activity and it is interesting to see how 

creative some of them are. Ideas for improvisation are found in the Primary School Units, the 

New Unesco Source Book for Science Teaching [2] and other teachers’ guides that happen to be 

available. 

An interview with students has revealed that the idea of improvisation is losing momentum. 

This could be due to the lack of qualified teachers as the part-time teachers and national service 

men do not understand the concept of improvisation; they are more interested in content. 

Professor Eric Rogers, at the Trieste Conference on Education for Physics Teaching in September 

1980, suggested that it is the teacher’s enthusiasm for science and not his teaching methods that 

wil inspire pupils. This seems to be true in developed countries where resources are available. 

But I am not sure what balance one should strike between making the teacher enthusiastic 

about science and showing him how he should teach it. 

Core Subjects 

In addition to their specialist subjects, all students are required to study English, a Ghanaian 

Language, Social Studies and Education. The syllabuses for these subjects are just as wide and 

detailed as the specialist ones and they can quickly become a burden to the students. Moreover, 

there is no relation between the core subjects and science teaching. All subjects stand as islands 

unto themselves. The teacher training course is not an integrated one. 

The use of the local language to teach science in the elementary schools is encouraged, as also 

is the idea of basing teaching on local culture. 

ASSESSMENT AND CERTIFICATION 

Formerly, NTTC assessed teacher training courses and gave a Ministry of Education Certificate. 

The three-year post-secondary course is now assessed and certificated by the University of 

Cape Coast. Assessment is both internal and external. Internal assessment is done by tutors 

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through continuous assessment of content, Project Work, Improvisation and Teaching Practice. 

Final Teaching Practice is normally assessed by a panel of tutors as external examiners on behalf 

of the University. The panel supervises distinction, borderline and a sample of average candidates. 

Project Work which is worth distinction or is borderline is examined by the Chief Examiner. 

The external examination is made up of two theory papers: one comprises objective and 

structured questions on content while the other paper comprises essay-type questions covering 

science content and teaching methods. 

Tutors from the various colleges write their questions and meet the Chief Examiner. After 

discussing and analyzing these questions, the Chief Examiner composes the two examination 

papers. The students are therefore examined on what they are taught. This method of assessment 

is similar to that of the Certificate of Secondary Education (CSE) Mode 111 Examination 

as used in the United Kingdom. These are written entirely by the teacher or a group of teachers 

on a syllabus designed by them and approved by the Examination Board. 

PROBLEMS ARISING FROM THE COURSE 

The results of the questionnaire to the Principals mentioned earlier revealed that staffing problems 

for science and mathematics were most acute. The lack of tutors oriented to the philosophy of 

the course is a serious problem. Ideas about the new methods of teaching are introduced into the 

colleges only to be handled in the traditional way. It is like pouring new wine into old bottles. 

Some science tutors find it difficult to teach integrated science and science teaching methods. 

They feel insecure with the new course. 

Students are very observant and can evaluate their tutors. From interviews I have held with 

them, most of them think that the quality of tutors is not up to their expectation. Most tutors 

are fresh from the diploma-awarding colleges and universities and have little experience in teaching 

at this level. The employment of part-time tutors from the neighbouring secondary schools to 

teach the course, the philosophy of which they do not understand, makes the students think 

that the course designers have under-rated its difficulties. 

The second problem is caused by the national service scheme which was started in 1973. 

Students graduating from the universities are sent to work in the departments other than those 

in which they wil be working eventually. The idea is to encourage young people to work in the 

rural areas so that they can become aware of some of the country’s problems. Some of these 

national service men are sent to teach in the training colleges. 

There is a high staff turn-over. National service men and part-time teachers change every year. 

The traditionally oriented tutors either go into education administration or go to head Junior 

Secondary Schools. An even bigger problem is the exodus of teachers to neighbouring West 

African countries. 

The varied differences in the standards of students is a difficulty for tutors. The entry qualification 

is four GCE ‘0’ level passes. These should include English Language, Mathematics and a 

science subject. Since most students wil prefer to go to a sixth form, those who enter for teacher 

training are normally those who cannot qualify for that. Consequently, there are students who 

have little background knowledge of science or mathematics or even none at all. It has been 

found [3] that 9 per cent of the students have biology, 10.7 per cent chemistry and 21.7 per 

cent physics backgrounds. How to bring this mixed-ability group to achieve the same objectives 

in three years is a very considerable problem to the tutor. The principals say that between 1 and 

3 per cent of entrants to the courses actually qualify. 

26 1


The fifth problem concerns the over-ambitious specialization. Studying Integrated Science, 

Agricultural Science and Mathematics to a level beyond ‘0’ level, in addition to a core of subjects, 

is difficult. The traditional problem of the pressure to complete the syllabus is still there and it is 

impossible to practise modern approaches to science teaching. Notes are still dictated to the 

students in order to ease their anxiety about the external examinations. The objective of educating 

teachers who can think scientifically and teach science practically is defeated. 

Not only the students but also the principals of the twenty four colleges running these courses 

have expressed their concern about the subject combinations. At an NTTC meeting, one member 

warned that what the government might take to be a ‘cheap commodity’ may turn out to be 

expensive in the future. It should be recalled that the main reason why the three-year ‘quasispecialist’ 

course was started was economic rather than educational. 

The syllabuses are too wide and time allocations are inadequate. The first year has seven 

periods (of forty minutes) a week, the second year has eight periods a week and the third year 

has nine periods. These periods are to be used for content, science teaching methods, project 

work and workshop practice! The Institute of Education, University of Cape Coast, attributes 

the failure of the three-year ‘quasi-specialist’ course to how the syllabuses were written. Prepared 

in a few days by hastily constituted panels without reference to methodology, they were ‘hotchpotches’ 

of the GCE ‘O/A’ level syllabuses. 

Lack of materials has been seen by principals, students and the government as a major problem 

militating against the course. Lack of textbooks and good libraries forces the students to depend 

on the ingenuity of the tutor. Private study ought to be a necessary ingredient of a course of this 

nature, but unfortunately the timetable is so tight that there is little time for reading. 

In most cases, the organization and administration of the college has not been modified to 

cope with the demands of the new course. The administrative staff should have been briefed on 

the aims and objectives of the course ‘so that the location of relevant materials or equipment 

for the colleges could be facilitated. The college itself would then cease to be an obstacle. The 

in-built resistance to change in established institutions must be recognized and removed before 

new programmes are started. This requires in-service training for all levels of the college staff. 

One of the problems arising from the course is the lack of co-ordination among the departments. 

Discussions and consultations have been absent. The support which might have been 

given or the talent which could have been pooled to teach the course with economy was absent. 

Improvisation, project work supervision and subsequent content areas which overlap are parts 

of the course which could have been taught by the team teaching approach. Boredom, confusion 

and even anxiety would have been removed. 

THE PHASINGOUT OF THE THREE-YEAR POST-SECONDARY ‘QUASI-SPECIALIST’ 

SCIENCE COURSE 

I think a brief account (based on published minutes [4]) of the events leading to the abandonment 

of the three-year ‘quasi-specialist’ course wil give an insight into the interaction that exists 

between the policy makers (the politicians) and the executives (the specialists - in this case, 

educationists). 

NTTC is an advisory body to the Ministry of Education on the training of teachers. It advises 

on the selection of students, courses to be run (both in-service and initial training) and education 

research. 

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When the proposals for the new education system, mentioned earlier, were made early in 1972, 

NTTC commented : 

1. The post-secondary teacher training course should be extended to three years since the 

existing two-year course did not provide adequate training. A three-year post-secondary course 

would be economical since few colleges would have to be started to run the various single 

specialist courses. 

2. ‘Curricula should be related to industry and social development in the country; and practising 

teachers and personnel from industry, amongst others, should be consulted. Account should 

be taken of manpower needs of the country’ (Minutes of 18 February 1972). 

3. Members recommended that a permanent body be set up to review education from time to 

time. This body should consist of members of the Planning Unit of the Ministry of Education, 

practising teachers, parents, representatives of industry, the Manpower Division of the Ministry 

of Economic Planning and all other bodies interested in education. 

4. Syllabus preparation for first cycle institutions should be decentralized i.e. they should be 

prepared at regional levels and co-ordinated by the Curricula and Courses Division. 

About six months later, November 1972, an NTTC member observed that a new curriculum 

for teacher training was being rushed into the education system. There had not been adequate 

preparation, consultation and discussions. He advised that innovations should have official 

endorsement before they were put into practice. 

This suggests that, from the outset, NTTC could discern the usefulness of the new programme, 

economically and educationally. The involvement of industry with practising teachers was an 

innovation. At the same time, NTTC could also discern the seed of destruction of the new programme 

- impatience. 

In May 1975, the Director of General Education reported that teachers’ salaries accounted 

for between 70 and 80 per cent of the budget of the Ministry of Education. To reduce this high 

cost, the government decided to stop specialist courses for qualified teachers, who were paid 

while in training, and to replace them with initial training courses which would include some 

specialization, but during which the students would not be paid salaries or allowance. The 

principals of the colleges reacted predictably: (1) they were not well-informed about the new 

programme and complained that it was being rushed through; (2) concern was expressed over 

finance, equipment and personnel; (3) subject groupings were too rigid; (4) they felt that it was 

very difficult for ‘0’ level students to study three sdbjects to ‘A’ level standard in addition to a 

core of subjects; it was therefore suggested that subject panels, composed of teachers from the 

colleges, should be charged with the task of writing the syllabuses; and (5) local languages spoken 

in particular areas should be taken into consideration if the programme was to succeed. Pressure 

to start the new programme immediately was brought to bear on the principals; they protested 

but to no avail. 

Subsequently, NTTC members felt that the university should have been involved in the drawing 

up of the syllabuses. Up to this time, no policy decision on the switch over from the two-year 

specialist course to the three-year post-secondary course had been taken. It appeared that the 

Ministry of Education was relying on the advice of personalities rather than following agreed 

principles. Instead of functioning as an advisory body, NTTC was merely a receiving one. Interaction 

had given way to a unidirectional process. 

A ten-member committee was set up to formulate guidelines for the colleges to help with 

subject groupings. The terms of reference for the committee were: (1) to formulate detailed 

263


objectives for the new teacher training programme; (2) to consider directives which were issued 

by the Ghana Education Service and to recommend appropriate action; (3) to determine the 

ratio of academic to professional studies; (4) to examine the subject groupings allocated to the 

colleges and suggest a workable limit to which these subjects could be taken; (5) to draw up a 

sample curriculum; and (6) to determine admission procedures. 

Members complained that the time limit for submitting syllabuses was too short. The Ministry 

of Education was persuaded to reduce specialization in subject areas from three to two. The new 

programme started in September 1975. Two months later, the government explained that the 

specialization in three subjects instead of one was for economic reasons i.e. to reduce cost in 

education. Orientation courses were to be organized for tutors of the various colleges on 

syllabuses, content etc. Money and accommodation were needed for such courses. 

Within a year, the problems were becoming apparent. In 1979 an analysis of the answers to a 

questionnaire that was sent to the principals revealed that: (1) a total of 128 I students finished 

the course in 1978, and 1032 in 1979 (from 11 colleges); (2) the subject combinations were said 

to be unrealistic; (3) staffing problems were acute in science and mathematics subjects; (4) specialization 

would be better if restricted to post-initial training; (5) the percentage of students qualifying 

for entry into the courses was between 1 and 3 per cent of the total entrants; and (6) the 

existing arrangement of external examinations was not acceptable. A committee was accordingly 

set up to examine the entire teacher training programme, to describe the problems and their 

causes and then to suggest solutions. The committee found that: (i) the programme was introduced 

without adequate preparation; therefore, there were no adequate equipment, materials or qualified 

staff; (ii) the principals, NTTC and the Institute of Education, University of Cape Coast, who 

were to implement the programme, were not involved in the planning; (iii) the ninety-two trial 

junior secondary schools already opened were unable to absorb all the teachers trained; those 

teachers who had therefore been posted to teach in the elementary schools were unwilling to 

work in them since they felt it beneath their dignity to do so; (iv) owing to inadequate staffing 

and equipment, the standard of the products of the programme was below the standard expected; 

and (v) it was difficult to get a sufficient number of qualified candidates for admission into these 

colleges. 

Since the junior secondary schools were now to be established gradually, the Education 

Service was no longer under pressure to train large numbers of suitable teachers through the 

three-year ‘quasi-specialist’ courses. The committee therefore recommended that: (a) the twoyear 

post-secondary course should be re-introduced since the students, after their secondary 

education, needed only methodology and professional training - a three-year general course is 

wasteful of time; (b) teachers for the junior secondary schools should be trained in the universities 

and diploma-awarding colleges; technical teachers wil be trained in technical schools and colleges; 

and (c) to solve the problem of equipment, tools, materials, etc., (i) the Ghana Education Service 

should get a bulk import licence; (ii) Unesco could be approached for assistance; (iii) a procurement 

unit should be established; (iv) the course content should be determined by NTTC, and 

(v) examinations should be conducted by NTTC. 

At the NTTC meeting of 19 September 1979, the report of the committee was discussed and 

the following decisions were made. First, a three-year programme without specialization would 

be started. Intensive teaching practice of not less than a full term in the final year should be 

conducted. Second, the new structure for teacher education in Ghana wil consist of: (i) fouryear 

post-elementary (post-first cycle), (ii) three-year post-secondary, (iii) three-year diploma 

and (iv) graduate teacher education. Third, the new programme would start with immediate 

effect in September I979 in all twenty-four colleges. Fourth, junior secondary schools would be 

staffed by post-secondary, diploma and university graduates and vocational and technical 

teachers. Finally, diploma courses should be for trained teachers only. 

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The Institute of Education, University of Cape Coast, reacted to the report of the committee 

as well as to the NTTC comments making four points. The three-year ‘quasi-specialist’ course 

should continue for a year while the new changes were being effected. The Institute did not wish 

to involve itself with the three-year general course. The failure of the three-year ‘quasi-specialist’ 

programme was due to poorly conceived syllabuses. Finally they warned that the new course may 

face the same problems of having no defined criteria on which to base the programme and no 

orientation courses for teachers. 

HOW FAR HAS THE PROGRAMME BEEN A SUCCESS? 

A questionnaire sent out to the products of the three-year post-secondary and two-year specialist 

courses of this college, Bagabaga Training College, revealed that most of them thought they were 

well equipped with the right skills for science teaching and that the course had aroused in them 

interest in scientific pursuits, increased their knowledge of science and made them committed 

science teachers. A few confessed that there was too much to do and this rather confused them. 

Most teachers thought themselves well equipped to teach science in elementary, junior secondary 

and secondary schools. Their non-specialist colleagues see them mo’stly as hardworking, cooperative 

and a real asset to the school, but the science organizers are seen as those who do 

little but are paid more! While a few thought of them as well prepared, most felt that they were 

only adequately prepared. Team teaching was agreed by all to be useful. All science teachers 

are disappointed by the discontinuation of the course because they think science teachers are 

needed in the elementary schools if the country is to progress in a scientific age. In spite of the 

difficulties involved in getting local materials, most science teachers think that the idea of 

improvisation learnt during the course has been an asset to them. 

Another questionnaire to the headmasters of the junior secondary schools also gave useful 

feedback. The teacher/pupil ratio in these schools ranges from 1 :50 to 1 :90. The science teachers 

in these schools are generally assessed as being fairly competent and enthusiastic about science. 

All the headmasters deplore the discontinuation of the course because they still need ‘middle 

level science teachers’. One of them showed his preference for the two-year specialist teacher. 

The number of teachers per school ranges between one and three. 

The results of these questionnaires seem to suggest that both the two-year specdist and threeyear 

‘quasi-specialist’ courses had achieved the objective of training science teachers to teach in 

the elementary and junior secondary schools and also to produce science organizers. Educationally, 

the courses have been a success. The lack of funds to provide the essential resources appears 

to have been less of a handicap to the colleges than the weaknesses in the course planning. But 

there were indications that it was more difficult for colleges remote from the administrative 

centre to provide satisfactory conditions for their courses than for colleges closer in. 

The existing teacher/pupil ratios indicate that more specialist teachers are needed right now. 

Is the solution to the problems of the programme to reduce the output of teachers, thus reducing 

the number of colleges, or rather to scrap the programme completely? This seems to be the issue 

at stake. 

DISCUSSION 

The Ghana experience as described above can provide ideas about mounting a programme for 

training science teachers for a new education system. The following points seem to emerge: 

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1. It appears that the relationship between politicians and educationists is an important 

element within any education system. The politicians may over-ride the expertise of the 

educationists because of their higher positions (which may be ephemeral), and the educationists 

are either cowed into submission or manipulated as puppets. Although the politicians may be 

aware of the right body of experts to go to for advice, they may prefer to listen to individuals 

who may merely be opportunists. 

2. It is necessary to have a permanent and autonomous body to review the education system. 

The composition of such a body should consist of the planning division of the Ministry of Education, 

practising teachers, teacher associations, the universities, parents, representatives of industry, 

manpower division of the Ministry of Economic Planning, religious bodies and other groups 

interested in education. The education system should be reviewed at intervals as determined by 

the body. Such a body could devise a feedback mechanism to follow the functioning of the 

system. In this way, any malfunction can easily be detected and action taken immediately. A 

reviewing body of this nature, and NTTC, should have the autonomy to function as intended. 

3. Any new programme should have in-built feedback mechanisms to ensure that it is working 

properly. Whether the evaluation of such a programme should be on-going or summative should 

be determined by the review body. This wil ensure that the programme is given a chance to 

function before being changed or even abandoned. 

4. In-service training courses for the heads of institutions, the tutors and administrative staff 

of these institutions on the aims and objectives, and on the mechanics of implementation of the 

course, should be provided. 

5. The ‘rushing through’ syndrome should be drastically controlled. It dissipates not only 

funds but also energy and causes anxiety which stultifies progress. 

6. Designing a curriculum for a new programme (which implies deciding on the aims and 

objectives, the philosophy, social and psychological bases of the course, methods of implementation 

and evaluation) is more useful than merely asking people to write syllabuses in haste. 

7. Whether the organizational structure of the institution needs to change to accommodate 

the new course must be considered. The organizational structure of a college may facilitate or 

may inhibit the functioning of the new course. 

8. Before the right type of candidates can be recruited for teacher training, career guidance 

counselling should be provided in the secondary schools. Unless this is done, there will always be 

dissatisfaction with students admitted to teacher training courses. An interview with our students 

indicates that there is no counselling of any sort in the secondary schools. A briefing course is 

also necessary when the students are about to start the course, for knowledge of the aims and 

objectives of the course may be motivating and may thus help them to build the right attitudes 

for themselves. 

9. The quality of tutors to teach in the training colleges should be high. Knowledge and 

experience are very important for teaching at this level. Since it is difficult to find many tutors 

of the right calibre in some of the developing countries, it seems wiser to maintain a few colleges 

only. 

10. The rate at which science teachers are produced should be related to the need. 

1 1. The cost of whatever course is planned should match the economic strength of the country. 

Over-ambitious plans may not have the chance to materialize while moderate ones can withstand 

economic storms. 

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CONCLUSION 

The training of science teachers for the elementary schools in developing countries is very 

necessary for progress. Politicians are aware of this, but they are normally very impatient and 

want to see their dreams materialize overnight. They exert undue pressure on the experts, i.e. 

the educationists, who are face to face with the reality. Malfunctions result. It seems, too, that no 

politician wishes to continue the policies of his predecessor. The experts in education should have 

the courage to tell in-coming politicians that their new ideas conflict with existing projects and 

should encourage them to facilitate existing programmes. How we can enhance the politician/ 

expert relationship to achieve positive scientific and national progress is a question worth 

exploring by science educators of every nation, and especially those of developing nations. 

The need for a permanent autonomous body to review the education system or the teacher 

programme is very necessary. This will provide a healthy check on those with personal axes to 

grind! There is security, confidence and solidarity in group work; fewer mistakes tend to be 

made by the group than by the individual. The proverbial saying that ‘two heads are better than 

one’ seems to be true. 

For a new education programme to be effective a plan of implementation should be determined. 

This should take place step by step, and each step should be evaluated before progress is made 

to the next. Some checks and balances should be included in this process to ensure that the 

politicians do not, through their anxiety, smother the programme. 

From the experience discussed in this paper, it can be realized that it is more effective to start 

innovations on the small scale, that is, to start with trial or optimal institutions. Scaling up or 

dissemination of this innovation to wider areas can then follow gradually after the defects revealed 

in the trials have been rectified. The process of education is a human activity which is not 

susceptible to management as a machine. 

My sincere thanks go to the Principal of Bagabaga Training College, the administrative officer 

and his staff and Dr. G.O. Collison, Head of the Science Education Department, and Dean of the 

Faculty of Education of the University of Cape Coast for their support and help in various 

aspects of this paper. 

REFERENCES 

1. GHANA ASSOCIATION OF SCIENCE TEACHERS (GAST). Report on the Workshop on Science Education, 

sponsored by Unesco, the Ghana Ministry of Education and GAST, Takoradi, Ghana, 6-1 8 April 1970. 

2. New Unesco Source Book for Science Teaching. Paris, Unesco, 1973 (3rd impr., 1979). 

3. SPEDDING, C. The Science Background of Students Entering the Three-Year Post-Secondary Teacher Training 

Colleges to Pursue the Science, Agricultural, Home Science Courses. 1978. 

4. NATIONAL TEACHER TRAINING COUNCIL (NTTC). Minutes ofkleetings. May 1972 to September 1979. 

5. GHANA. MINISTRY OF EDUCATION. The New Structure and Content ofEducation for Ghana. Accra, 1974. 

267


How to overcome the dilemma of physics education 

D. NACHTIGALL. 

THE PRESENT SITUATION OF PHYSICS EDUCATION 

One of the most prominent physics teachers of our day, the first recipient of the ICPE Medal for 

Physics Teaching, Eric M. Rogers, describes the motivational starting position of science teachers 

for their daily work at school or college as follows [ 11 : ‘Those of us who teach usually trust 

optimistically that what we say to students wil be learned, that what we show will be remembered, 

that the methods we demonstrate will be applied, that the values we preach will be appreciated: 

in general, that all our didactic output wil go to build an edifice of education that will last our 

pupils all their lives.’ But, he continues: ‘Students remember some of the material issued to them 

- but we wonder how much they remember and how long they remember; and we wonder what 

form later memories take. . . . Only for a few does our elementary teaching of science in school 

or college build a basis for intellectual growth or technological use.’ 

Other physics teachers have similar impressions about the outcome of the activities of science 

teaching. In physics, especially, the situation is considered to be highly unsatisfactory. At the 

International Conference on Physics Education, 1975 in Edinburgh, P. Black [ 21 stated: ‘There 

is evidence that students studying sophisticated physics often have a poor understanding of basic 

concepts.’ Graduates for entry to M.Sc. courses ‘ . . . often make gross errors in the simple 

qualitative description of processes and topics of which their courses had included detailed study.’ 

Asking ‘questions testing understanding of the basic concepts of Newtonian mechanics to 

university physics students in their first and third years, the results were uniformly poor, the 

only difference between the two groups being that first year students justified their errors with 

qualitative arguments whereas third year students used formal and mathematical language to 

explain the same mistakes.’ 

At the same conference, J. Ogborn [3] specified his four worries about students coming to 

university: ‘they do not know enough; they do not understand what they know; they do not 

understand what physics is and how it works, and they are unable to learn effectively by themselves.’ 

Five years later, at the 1980 ICPE Conference in Trieste, the situation was considered to be no 

better. In the conference report [4], the following despairing cries were recorded: ‘Physics- 

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Teacher education: a dilemma 

where nothing happens! - who would want to learn that?’ ‘Only Greek and Latin are less popular 

than physics!’ ‘Most pupils forget the physics they learn at school.’ 

A. Arons [5] recently described the situation with the statement that ‘the majority of 

students. . . eventually come to see all “knowledge” and “understanding” as the juxtaposition of 

memorized names and phrases.’ This has certainly nothing to do with ‘scientific literacy’ [6]. 

All those who observe the practice of daily physics classes critically wil probably agree with 

the assessment of H. Feshbach, Past President of the American Physical Society, and R. Fuller, 

President of the American Association of Physics Teachers: ‘We have growing concern with the 

deterioration in both the quality and the quantity of secondary physics education. . .’ [71. 

ASPECTS OF THE DILEMMA 

Why doesn’t physics become an integral part of what manifests itself as the result of education at 

schools? Many speculations, many diagnoses and several theory-based attempts at analysis have 

been published in the last decade. Their substance can be described under the following seven 

headings: 

Physics as a subject of school learning arouses aversion in young people: 

‘ . . . already in the high schools young people are inclined to show less interest in scientific 

subjects, particularly physics, perceived as a cold study of things, based on artificial assumptions, 

far from the human implications of present day life and, what is worse, responsible for all the 

evils of the past and present historical issues (war, pollution, food and population problems, and 

so on.)’ [ 81. 

Better curricula did not achieve wider application: 

‘Curriculum projects have failed because they were too small, too short, attempted too much, 

and created a gap that was too far from where teachers then were’ [9]. 

The instructional material does not fit the demands resulting from research in the field of 

cognitive psychology: 

‘ . . . very basic cognitive difficulties (are) shared by many students in introductory physics 

courses. . . . It is a fact, however, that existing instrbctional material offers teachers very little 

help in overcoming these formidable obstacles to learning and understanding’ [ 101. 

In oral instruction Physics is presented as a set of formal procedures which most pupils are 

unable to understand because they have not yet reached the appropriate level of thinking ability: 

‘The cry of many college science teachers that students can’t think could be attributed to this 

intellectual dichotomy: course content presentation at one level of intellectual thinking and 

students’ thinking ability at another level’ [ 1 1 1. 

‘Purely verbal indoctrination has left essentially no trace of knowledge or understanding. .. . 

Students are being told about the “fascinating” particles of high energy physics, with jargon 

about interactions, angular momentum, mass-energy relations, quantum transitions, and 

uncertainty principles while they have yet achieved no conception of what is meant by velocity, 

acceleration, force, mass, energy, or electrical charge, much less of how we obtain evidence 

regarding the structure of matter on a scale that transcends our senses’ [ 51. 

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‘Who would be brave enough to offer a course reduced far below the local or national norm 

and to defend his action by claiming that his students were going to learn and understand more 

physics because of the change?’ [ 21. 

One special aspect of too much and too abstract material which is of no obvious importance is 

the speed with which it is presented in the class room: 

‘ . .. that a student’s incapacity in a particular subject is owing to a too-rapid passage from the 

qualitative structure of the problem. .. to the quantitative or mathematical formulation normally 

employed by the physicist’ [ 121 . 

A. Arons, in a characteristic flash of caustic humour, characterized a common style of university 

professors who teach future physics teachers (who then teach as they were taught) in these terms: 

‘It is the basic premise of the vast majority of introductory physics courses taught at the present 

time. . . that, if one takes a huge breadth of subject matter and passes it before the student at 

sufficiently high velocity, the Lorentz contraction wil shorten it to a point at which it drops into 

the hole which is the student’s mind’ [ 131. This points to one problem of teacher education 

which seems to me to lie at the root of the matter. 

Teacher education is not directed towards the teaching of children; it is not competency-based: 

‘We feel that there is a huge gap between the abstract and theoretical lectures which teacher 

trainees receive in the universities and the actual practical teaching which they must perform. 

This gap is something which many, if not all, teacher trainees are unable to overcome’ [ 141 . 

The Unesco Handbook for Science Teachers describes clearly the disastrous role of many of 

the university teachers who teach future teachers: ‘The secondary teacher thinks of his or her 

university instructors as models to emulate and therefore “teaching is telling and learning is 

listening” in all too many science classrooms’ [ 151 . P.J. Kennedy, in his Outlook from Trieste 

[4], took the point when he wrote ‘. . . having selected our teachers merely for their ability 

to do physics and having spent so much time on training them to do physics, we then require 

them to display an intimidating range of other qualities, skills and abilities, and ask them to 

perform tasks widely different from, and perhaps even incompatible with, much of their training.’ 

Children play a subordinate part: 

If teacher education is responsible for the negative development of physics education in the past, 

then we must focus first on this if we wish to make improvements. But teacher education must 

not be seen as an isolated, self sustaining, teacher-centred activity. It seems that the demands and 

needs of children are not sufficiently taken into consideration in the daily practice of teacher 

trainees. One indication of this is perhaps the fact that in a concluding paper on physics education 

in the chapters ‘Problems and Challenges’ and ‘Suggestions for Action’, [9] the word ‘teacher’ 

appears fifty-eight times, whereas the words child and pupil are used four times only! 

What is the way out of this dilemma? Answers to these questions cannot be given in the framework 

of physics alone. In the process of teaching and learning physics, competence in physics and 

in the basic concepts of other natural sciences is necessary but by no means sufficient for giving 

adequate answers. Competence in the fields of the philosophy of education, pedagogics and 

psychology and in human relationships are of enormous importance [ 161. The contribution of 

these disciplines must not be seen in isolation but should be closely related and directed towards 

physics and education. We, in Dortmund, are developing the education of our physics teachers 

on the basis of a close collaboration between these different disciplines [ 171. The particular 

items of our approach are strongly influenced by our underlying philosophy of education. 

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ELEMENTS OF AN EDUCATIONAL PHILOSOPHY 

Article 26 of the United Nations Declaration of Human Rights expresses the basic principles 

which determine all our theory and practice related to physics teaching and physics teacher 

education, whilst J. Piaget’s book To Understand is to Invent [ 121 and J. Dewey’s writings on 

Educational Philosophy have been powerful influences. This Article states: ‘Every person has the 

right to education. . . . Education shall be directed to the full development of the human 

personality. . .’ 

But what does ‘full development of the human personality’ mean? The development of an 

individual is the result of the combined effects of heredity and social interactions. Social interactions 

include all organized and unorganized interactions of the individual with other individuals 

or groups in the society. A large part of the organized interaction takes place in the schools. 

Schoolmates and teachers are partners in these interactions. Man-made boundary conditions 

exert a tremendous influence on these interactions. These include school organization, curriculum, 

rules and regulations concerning books, equipment, time, gradings, .examinations, numbers of 

pupils, etc. Government and, in democratic states, the society are responsible for these factors. 

It follows that the development of an individual depends on the conditions provided by the 

society. Full development of the human personality means that society must do as much as 

possible to enable an individual to integrate himself spiritually, socially and physically with 

nature, culture and nurture. This makes it possible for the individual to become conscious of the 

role played by the concept of an autonomous self. He must then be helped, e.g. by teachers, to 

achieve a dynamic equilibrium of internal states which can be characterized by the questions: 

What am I? What am I not? What would I like to be? What would I not like to be? What are the 

relations between my external conduct and my internal needs? 

This individual aspect must be combined with the general needs to promote the unity of all 

peoples and to enable man to survive in dignity. This is, from my point of view, the educational 

essence of the development of human personality. 

The education process leading towards the self-concept has several aspects. Two of them are 

closely related to Science: ethical development and intellectual development. The relations 

between the elements of both aspects are shown in the following schema: 

Science-related educationa I 

activities towards a self - 

Ethical 

Development 

I 

/ T 

Interaction with 

the environment 

lntellectua I 

Development 

Thought -patterns 

6 

Se If - concept 

27 1


The schema indicates that intellectual and ethical development are seen, not as isolated roads, 

but as interactional, mutually supporting processes. This has a strong influence on both the 

theory and practice of physics education. 

What place has physics, or science in general, in this context? (1) Science represents a special, 

important, and successful kind of interaction between man and nature. This interaction has 

value as an intellectual activity in itself. (2) Science is a cultural activity, the source of important 

spiritual movements, and the results of science are part of the hard core of Western culture. 

(3) Science is an activity leading to emancipation, to education as world citizens, making possible 

participation in decision-making processes affecting the future of mankind. (4) Science is a good 

preparation for employment, an important activity from the social and economic point of view. 

(5) Science is a prominent means of developing thinking and enhancing creativity; for me this is 

the strongest justification for physics classes in schools. (6) In conjunction with ethics, science in 

general and physics in particular are, therefore, essential elements in the development of a selfconcept. 

THE CAPACITY OF PHYSICS TEACHER EDUCATORS 

What follows from these elements of an educational philosophy for teacher education? We need 

physics teachers who can implement physics as a living element in our culture, and they should 

be involved in the development of a self-concept in the young people. The activities within the 

framework of physics education should be directed, in the main, towards intellectual development. 

But they must always be seen in the context of the inter-related left side of the schema, 

the ethical development. 

Many books have been published on intellectual development. J. Piaget stands as a symbol 

for the role of psychology in physics education. Piaget-based curricula, textbooks, test batteries, 

etc., have been written. All these have failed to prevent the development of the present situation. 

It is - at least in my country - very hard to get practising teachers back to new learning. New 

ideas, the results of educational research and innovational proposals from the side of curriculum 

developers are accepted by a very few individuals only. Many so-called ‘experienced teachers’ 

see it as an imposition to call in question what they have done for so many years, even if this 

never had a basis in theory. If one is in power, one does not want change! The lever must, therefore, 

be applied in pre-service teacher education. It is in the hands of physics teacher educators. 

Here is a catalogue of principles, methods and activities which characterize the work of our 

group at the University of Dortmund. It is the result of our practical experiences as teachers in 

schools and at university and of the reflection of these experiences against the background of 

our educational philosophy. 

Physics teacher educators should have continuing experience in classroom practice. 

It is not sufficient to visit a teacher in his class from time to time. It is necessary to act as the 

responsible teacher in physics classes for some hours per week. This enables the teacher educator 

to integrate his experience or problems in practice with his work at the university. In addition it 

makes it easier to get in contact with full time school teachers, to influence them and to develop 

a better feeling for possible innovations. 

The physics teacher educator must have competence in simplification. 

It is self-evident that a teacher of future physics teachers needs competence in physics. However, 

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if physics is presented in such a way that teaching is telling and learning becomes listening, then 

the subject competence of the physics teacher educator must include a special component: 

the ability to simplify. Such simplification (in German ‘Elementarisierung’) means to provide 

access to the ideas of physics without formalism. Only very few formalisms, and these simple, 

can be used in high schools. The teacher must first use the natural language and then introduce 

the concepts of physics step-by-step in accordance with the intellectual development of the 

learner. Simplification requires the ability to express the idea in a language which is understandable 

and meaningful to pupils. Let me give an example which has been described by the German 

physics educator M. Wagenschein [ 181 . 

Sixty students of a German University, all future teachers in secondary schools, had been 

asked to explain the law of free fall in words. The formula s = 1/2 gt2 had been put on the 

blackboard. The goal was to describe the physical content, the idea, in words and without losing 

exactness, avoiding physical terms and symbols so that pupils of the appropriate age could understand 

it. This is a normal task of a practising physics school teacher and should not turn out to be 

difficult. Every physics teacher educator can imagine what the outcome would be were he to ask 

his students this question. Probably something like: ‘The distance travelled by the falling body 

is proportional to the square of the time. . . .’ But this is not a translation of the physical content 

of the formula into words; this is not an idea intelligible to these pupils. What Wagenschein hoped 

to hear and what the students were unable to express was something like the following: ‘Spread 

two fingertips a small distance (say 5 cm) apart. Suppose this to be the distance the body falls 

during the first time unit. Then the body falls during the second time unit - not the two-fold 

and not the four-fold - but the three-fold distance, then in the third time unit the five-fold 

distance, then the seven-fold, the nine-fold and so on.’ The odd numbers appear as Galileo had 

already described. This is a ‘simplification’. It requires the teacher educator to have a deep 

understanding of physics. The ability of juggling with abstract formalism is not sufficient. It does 

not help them to acquire this essential teacher competence. 

Another example out of my own experience: last spring, one of my physics teacher trainees 

had his practice period at a senior high school. He was giving a physics class with ninth graders 

(1 5 year-olds). The subject was the determination of densities of different material with different 

shapes. The pupils were experimenting in groups. One group figured out that the density of wood 

was 1.7, their neighbours obtained the figure 0.6. I asked which of the two was right. Both 

insisted they were! I asked what density means. The answers were: ‘volume divided by mass’ 

and ‘mass divided by volume’. I asked again, which answer would be right. Both groups decided 

not to argue but to look into the book, to ask the formula, to leave the decision to an authority. 

These pupils had not grasped the idea of density. In addition they had perhaps different mental 

pictures of volume and/or a wrong concept of mass. The teacher had probably never learned to 

simplify, to express the idea of density in a way which made sense to pupils. Perhaps he had not 

learned it because his own physics teacher found it to be far below his academic level and 

incompatible with his dignity to see a problem in such a ‘simple’ thing as density. But it is 

extremely important to confront future physics teachers with such exercises. In our physics 

courses, students are given many exercises to do of the sort: ‘Explain in your own words the 

phenomenon of buoyancy.’ ‘Assume you want to explain to a tenth grader (1 6 year-old) the term 

acceleration. How would you do this?’ ‘How would you explain to a seventh grader (13 year-old) 

the difference between average and instantaneous velocity?’ ‘What will a fifth grader (1 1 year-old) 

probably answer if you ask for the difference between heat and temperature?’ 

To a physics teacher trainee who has only 6 or 8 semester periods at the university for picking 

up his professional competence it is more important to spend time in such exercises than to try, 

in nuclear physics, to prove mathematically that for a spherically symmetric charge distribution 

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the quadrupole moment vanishes. The subject competence of a future physics teacher has from 

the quantitative and from the qualitative point of view dimensions other than those for a future 

physicist [ 191 . 

The physics teacher educator must have a psychological competence. 

Every teacher-learning process which is intended to contribute to the full development of the 

human personality must take into consideration the psychological disposition of the individual 

learner. The school teacher should know as much as possible about this disposition. Psychology 

departments at universities offer many different courses. But psychologists normally do not 

understand very much physics. If, for example, the psychology of cognition or developmental 

psychology is taught independently of physics, without any relation to physics, and in a way that 

has scarcely anything to do with the profession of a classroom physics teacher, then it is left to 

the student to put together and to inter-relate what university teachers are unable to integrate. 

In most cases, this does not work. Skills in physical experimentation and some psychological 

competence make it possible to imagine what kinds of insight a pupil can get when an experiment 

is done in the physics class. Only the knowledge of physics and a psychological background 

can enable an instructor to sensitize teacher trainees to the important task of the analysis of 

pupils’ reactions to physics phenomena. 

Let me give another example: I have asked sixty-seven fifth graders (1 1 year-olds) about their 

understanding of the phenomenon of free fall. If a lead ball falls from a window on the third 

floor down to the ground, what can be said about the velocity as it passes the second and first 

floor? The spectrum of answers was very wide. 

Fifty per cent said that the ball would fall faster at the first floor because ‘it gets more and 

more drive’; ‘it needs a take-off run’; ‘it does not yet have its right velocity at the second floor’; 

‘it has not fallen long enough at the second floor’; or ‘at the second floor it is still getting drive’. 

Twenty-five per cent of these pupils argued ‘more downwards as the earth attraction is 

stronger’; or ‘whether the ball is heavy or light, the earth attraction is so strong that it pulls down 

the ball anyway’. 

Forty-seven per cent of the pupils believed that the velocity is the same at both levels, because 

‘the ball keeps its weight constant’; ‘the earth attraction is the same at both levels, therefore the 

velocities are the same’; or ‘a ball doesn’t have brakes or a throttle, so it can’t slow down or 

speed up’. 

Two of the pupils did assume that the ball ‘already starts slowing down at the first floor’ 

because it is about to land. 

A knowledge of physics is required to analyse how correct statements were made following 

wrong arguments and how sound arguments can lead to incorrect conclusions. A background 

in cognitive psychology is required to understand how concrete reasoning schemata, obtained 

and applied successfully by concrete interaction with the surroundings, are applied to an event 

which the pupils were required to imagine. Both subject competence and psychological knowledge 

are necessary to make student teachers aware of this important aspect of teaching. 

The physics teacher educator must be able to create a stimulating learning atmosphere free of 

fear in his own class. 

A teacher can’t get information about the background of his pupils, about the cognitive structures 

in the minds of children, about feelings, norms and values of young people, if these do not 

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emerge into the open, if the teacher is not trusted, if the students are not treated with emotional 

warmth and in an intellectually honest way. ‘ . . . teachers . . . must encourage the pupil to talk 

and they must themselves learn to listen to what the pupil says. This is not easy, for the strong 

tradition in school science writing is formal, impersonal and adult’ [ 201 . 

But listening is not enough. The teacher must be able to respond in an appropriate way, to 

adapt himself mentally to the reasoning level of the pupils whose thinking is limited by their 

assimilation schemata. Otherwise he or she may be able to indoctrinate, i.e. to let the pupils 

learn facts and laws which will be memorized for the examination and then forgotten, but unable 

‘to interpose between physics and the cognitive structure of the learner’ [ 21 ]. ‘These problems 

must be tackled in teacher training by helping student teachers to learn to talk with and listen to 

young pupils. . .’[22]. 

Probably in no other respect is it more important for the teacher to act as a positive model 

than in the field of creating an open teaching-learning climate. The well-known tendency of many 

physics professors to over-estimate the learning capacities of their students, to express pride 

about the sophistication of physics, to try to develop the consciousness that physicists form an 

dite and to assume that everybody who does not fit the standards of this Clite is second class 

tends to establish a negative model. Physics school teachers, whose scientific self-esteem demands 

that they copy this attitude before their physics classes, out of which more than 95 or even 99 

per cent are not going to become physicists, have a disastrous impact on their pupils. I remember 

a physics professor, well known in my country as a respectable specialist in his field, who 

resigned at an age of 65 and started physics teaching at a senior high school. He was quite successful 

with thirteenth graders (19 year-olds). These were highly motivated and committed to an 

advanced course. But with the seventh graders (1 3 year-olds) it was terrible for both teacher and 

pupil. He felt this and he told me that in his opinion ‘none of the seventh graders are qualified 

enough for the gymnasium.’ 

Before a physics teacher can use physics as a means for education, as an important element for 

the development of a self-concept, as a useful tool for the development of reasoning patterns, etc., 

he must be enabled to open the child’s mind, to make his pupils willing to reveal what and how 

they are thinking, to listen, to understand, and to analyse what they have to say or what they 

put in writing when they are asked by the teacher to articulate the way they are reasoning. 

The more a teacher trainee finds that his own schemes of thought, reasoning patterns, models, 

prejudgements and wrong arguments are handled tactfully, his misconceptions, etc. are improved 

and corrected successfully, the more he wil be able and willing to adopt this attitude as a 

principle of human-optimal learning [24]. To me, this particular teacher competence is the key 

competence for the improvement of physics education. The teacher educator must do his best in 

this respect. But the comment made by E.J. Wenham about school teachers also applies to him: 

‘The teachers themselves have it in their hands to implement a change,. . . But they were themselves 

successful within the system which they now operate and may form a largely conservative 

element in Zhat system.’ [ 201 . 

Force, impetus, drive, motivation or whatever else a teacher needs to change for the better 

should come from his ethical position, from his educational philosophy, and from his own selfconcept 

as a helper of human beings. There are very few professions burdened with such far 

reaching responsibility! 

The physics teacher educator must provide his student teachers with a general model of teaching 

which accords with his educational philosophy. 

If the teacher educator wants his ideas about the teaching-learning process to be put into practice 

27 5


by his students, he must develop in his own practice a model of teaching to present to his 

students. They should not take it as a prescription but as a guide-line through which they can 

develop their own teaching style. Since the style of a teacher expresses a part of his personality, 

prescriptions of style suppress the personality. This may lead to the loss of authenticity and so of 

credibility. 

It is reasonable to organize the teaching-learning-process in such a way that psychologically 

founded stages are taken into consideration. R.M. Gagne [ 231 has listed such stages: 

(1) Gaining and controlling attention. 

(2) Informing the students of expected outcomes. 

(3) Stimulating the recall of relevant background. 

(4) Presenting the stimulus situation. 

(5) Offering guidance for learning. 

(6) Receiving and providing feedback from learning. 

(7) Appraising performance. 

(8) Providing for the transfer of knowledge. 

(9) Ensuring retention. 

The scheme is rather general. It can be adopted by authoritarian teachers, who prefer teachercentred 

classes, and also by teachers with a more democratic teaching style. 

The credibility of a physics teacher educator, however, is much higher if he presents a model 

for physics teaching which is consistent with his theory and educational philosophy and through 

which he practises what he preaches. The roots for such a model can be found in publications of 

J. Piaget, J.W. Renner, R. Karplus and M. Wagenschein. The philosophical, psychological and 

pedagogical implications of the model (which is outlined below) are the subjects of seminars in 

Dortmund. The students can put it into practice in the framework of our Didakticum which is 

described elsewhere [ 17 1 . 

OUTLINE OF A MODEL FOR PHYSICS TEACHING 

The didactic principles set out below stem from the basic position in educational philosophy 

given earlier: 

Reciting the stuff to be learned - is not teaching. 

Storing something away in your memory - is not learning. 

Ability to memorize what is stored away - is not evidence of understanding. 

To teach is - to arrange situations in which the learner can discover structures for himself. 

To learn is - to behave actively. 

Acts of learning manifest themselves as changes in self-directed, individual behaviour dispositions. 

Understanding is - insight into the reasons for the possible results of action [241. 

A model of physics teaching having regard to these principles [ 161, and one furthering ‘the full 

development of human personality’ can be set out under the following ten teacher/pupil activities. 

27 6


These include the ‘Four Cs’ of A. Baez [25], the development of which enriches the quality of 

life, namely Curiosity, Creativity, Competence and Compassion: 

( 1) Localize, distinguish, appraise. The particular wil be discovered in the general. Something 

in the surroundings, a phenomenon, wil be brought into focus and recognized as something 

particular and meaningful. The particular is extracted from the general. Curiosity wil be aroused. 

(2) Activating elements of personal character. Anchorage points for mental structures wil be 

uncovered. The following should be established: what is already known about the phenomenon, 

what contact one has already had with it, what degree of familiarity exists, what effect the 

phenomenon has on life. 

(3) Creatingawareness ofproblems. A confrontation wil be arranged between the phenomenon 

and the individual’s cognitive structures. The pupils find that the phenomenon is problematic, 

that the connection between the external and imagined behaviour of the phenomenon has not 

been established in any self-evident way. So an internal inspection of the activated mental 

structure is necessary as is an assessment of the extent of its usefulness in problem solving. 

(4) Assimilations and explaining. That inspection can show that perceptions can be consistently 

incorporated into existing, activated cognitive structures; that the phenomenon can be 

explained; that insight is available into the causes of real or potential results of action. 

(5) Cognitive dissonance can be aroused. Inspection may also reveal that the existing 

structures are inadequate. Awareness of cognitive imbalance arises from this. In an atmosphere 

free from anxiety, in which self-confidence has been developed, this dissonance can be a very 

strong source of further motivation. 

(6) Accommodation. Modifications, adjustments, extensions, re-arrangements of cognitive 

structures will be undertaken. It is creatiye imagination which here yields the best results in the 

form of new, more complex, more comprehensive, more productive ways of thinking, a new, 

more complex schema. 

(7) Establishing cognitive harmony. The new schema is recognized as productive. Its application 

leads, with growing competence, towards autonomy. Mutual help, not competition, 

characterize this process, where everybody is willing to act as a compassionate helper, supporter, 

and friend. 

(8) Conceptualization. The new schema is appropriated and internalized. With use in various 

areas the extent (and the limits) of its application are realized. 

(9) The process is made conscious. The learner becomes aware of the process that has been 

going on. He comes to know that there have occurred mental changes which have led to greater 

skill in productive interaction with the world. In this process, the important role of ’wrong 

answers’ will be brought out, together with the importance of ‘crazy hypotheses’, of admitting 

and discussing formerly private difficulties, of recognizing and expressing irrational prejudiced 

ideas. 

(10) Structuring the environment. A new concept is used for structuring the non-school 

environment and school affairs. Hence the general can be discovered in the particular. The role 

of new concepts in the development of cognitive structures and their possible influence on 

ethical development wil be considered. 

277


CONCLUSION 

My proposals for an escape from the physics education dilemma are directed towards the education 

of physics teachers. Apart from reliable subject competence, the teacher trainer needs 

practical experience in the school classroom, must learn to simplify subject content, can’t be 

successful without a certain psychological competence, must be able to create in his own classroom 

an open and stimulating learning atmosphere free of fear, and owes his student teachers a 

general model of teaching which is in accordance with his educational philosophy. 

This includes a range of expertise not normally possessed by physics professors. Practical 

pedagogics, sociology, psychology, philosophy and general didactics are, besides physics, the 

main constituents of such an inter-disciplinary approach. In addition, history of science, linguistics 

and information theory often contribute to the improvement of a physics teacher’s education. A 

single person is overtaxed if he is to engage deeply in all these disciplines. A physics teacher 

educator, normally being at home in physics, should try to get access to one or two of the other 

subjects so that co-operation with specialists of these fields becomes possible. This teamwork 

of professionals from different disciplines must be done in a physics-specific way. In Dortmund, 

we have such a team. In our Didakticum, a psychologist and a specialist of general didactics 

join us. They have learned some physics in the Didakticum so that they can relate their contributions 

closely to physics. Another psychologist offers, in teamwork with us, seminars on ‘psychological 

problems of learning physics’. A philosopher guides seminars for our physics teacher 

trainees on such topics as ‘Hypotheses and Scientific Laws’ or ‘Ethical Problems with Respect 

to the Development of Science and Technology’. Willingness to learn from each other is a requirement 

which must be met, otherwise this kind of co-operation would not work. 

This is our way out of the physics education dilemma. It is determined by a lucky coincidence 

which made it possible to constitute our team. But a statement of J. Colbeck [ 261 must certainly 

be taken as true by all physics teacher educators: ‘. . . we, as physicists in the universities, colleges 

and schools, have to look for the remedy in ourselves. We must have made the teaching of physics 

look unattractive or we have allowed it to become so. Perhaps we have also made physics itself 

look unattractive in spite of our own enthusiasm for it or, worse still, because of our enthusiasm 

for it. (We may have seemed to put nuclear physics before people, for instance.)’ 

REFERENCES 

1. ROGERS, E.M. Improving Physics Education Through the Construction and Discussion of Various Types 

of Tests. Paris, Unesco, 1972. (Unesco doc. SC/WS/506.) 

2. BLACK, P.J. ‘Physics Curricula and Courses at the Undergraduate Level.’New Trends in Physics Teaching, IZI. 

Paris, Unesco, 1976. 

3. OGBQRN, J.M. From School to Higher Education. New Trends in Physics Teaching, IIZ. Paris, Unesco, 1976. 

4. KENNEDY, P.J. The Outlook from Trieste. ICPE International Newsletter, No. 8, 1981. 

5. ARONS, A.B. Using the Substance of Science to the Purpose of Liberal Learning. Journal of College Science 

Teaching, Vol. 10, No. 2, November 1980. 

6. RIGDEN, J.S. What is Scientific Literacy? American Journal ofphysics, Vol. 49, No. 2, 1981, p. 107. 

7. FESHBACH, H.; FULLER, R.G. University-School Coaperation.Physics Today, April 1981, p. 11. 

8. FERRETTI, M. Pre-Service and In-service Training of Secondary School Physics Teachers. New Trends in 

Physics Teaching, III. Paris, Unesco, 1976. 

9. REAY, J. Diffusion of Innovations in Physics Education into National Systems. New Trends in Physics 

Teaching, ZII. Paris, Unesco, 1976. 

10. ARONS, A. Thinlung, Reasoning and Understanding in Introductory Physics Courses. In: U. Ganiel (ed.). 

Physics Teaching, GIREP-Conference Report, Jerusalem, 1980. 

278


11. COLLEA, F.P.; NUMMEDAL, S.G. Development of Reasoning in Science. Journal of College Science Teaching, 

Vol. 10, No. 2, November 1980. 

12. PIAGET, J. To Understand is to Invent. New York, Grossman Publishers, 1973. 

13. ARONS, A. Cognitive Level of College Physics Students. American Journal ofphysics, Vol. 47,1979. 

14. KoGANEI, M. Improvement of a Teaching Skill Training System for Teacher Education. Journal Science 

Education in Japan, Vol. 2, No. 4,1978. 

15. Unesco. Unesco Handbook for Science Teachers, p. 79. Paris, Unesco, 1980. 

16. NACHTIGALL, D. Physics Teaching and Human Optimal Learning. In: Ch. P. McFadden (ed.), World Trends 

in Science Education. Halifax, Atlantic Institute of Education, 1980. 

17. NACHTIGALL, D. Physics Teacher Education in Dortmund/Germany. The Physics Teacher, Vol. 18, November 

1980. 

18. WAGENSCHEIN, M. Natuiphanomene sehen und verstehen. Stuttgart, Klett, 1980. 

19. SCHWANEBERG, R. Die Unbestimmtheitsrelation als Schlussel zurn Verstandns elementarer Quantenphysik. 

Frankfurt/Bern, Lang, 1980. (This book is a representative example of what is meant by ‘other dimensions’. 

It shows our approach to Quantum Mechanics for teachers.) 

20. WENHAM, E.J. New Approaches to Teaching and Learning in Schools,. New Trends in Physics Teaching, III. 

Paris, Unesco, 1976. 

21. JUNG, W. 1st elementarisierter Physikunterricht noch zeitgemass? Der mathematische und natunvissenschaftliche 

Unterricht, Vol. 33,No. 8,1980. 

22. International Newsletter, No. 8, April 1981. Edinburgh, International Commission on Physics Education 

(ICPE). 

23. GAGNE, R.M. The Conditions of Learning. New York, Holt, Rinehart and Winston, 1970. 

24. HEEGE, R. Sprache - Wahrnehmung - Information und Fachdidaktik. Frankfurt/Bern, Lang, 1979. 

25. BAEZ, A.V. Curiosity, Creativity, Competence and Compassion - Guide-Lines for Science Education in the 

Year 2000. In: Ch. P. McFadden (ed.), World Trends in Science Education. Halifax, Atlantic Institute of 

Education, 1980. 

26. COLBECK, J. What’s Wrong with Teaching Physics? Physics Education, November 1979, p. 394-8.


A curriculum development/teacher training scheme based 

on the study of solar energy 

P.E. RICHMOND. 

THE EDUCATION OF TEACHERS 

The education or training of teachers takes place before they have taken up a teaching post (initial 

training) and also, increasingly, during their time as practising teachers (in-service). In-service 

education is most effective when teachers feel a well-defined need for advice and assistance. When 

change is in the air, when new projects or substantially new examination syllabuses are being 

introduced, in-service work is easy to arrange. Unfamiliar content and unfamiliar teaching 

methods can be introduced to teachers by ‘experts’, preferably those who have been closely 

associated with the developments, alternatively by teacher trainers in sympathy with a project’s 

aims and methods. Teachers who have helped to prepare trial materials and who have tried out 

teachers’ guides, pupils’ guides and experiments with their classes carry conviction and are always 

popular. College lecturers who have kept up with developments and kept in touch with schools 

are usually in sympathy with innovations and use published material to good effect. But things 

are not as easy as they were. 

In the United Kingdom and many other countries, the day of the ‘Big Project’ is over. Teacher 

educators no longer have an easy source of novel materials to present to practitioners. Nevertheless, 

in-service education is still needed. Changes in the future are likely to come about in less 

spectacular fashion than in the sixties and seventies. The science curriculum will surely change 

in response to new scientific knowledge, new social demands and improved understanding of 

effective educational practices; teacher training courses must change from merely presenting 

project materials to a more creative style. The challenge is a substantial one. In the absence of 

well-defined innovations launched nationally through well orchestrated press releases and television 

and radio interviews, interest must be generated locally and personal decisions about 

courses wil need to be made. For these decisions to lead to popular courses and effective change 

in classroom and laboratory practice, course organizers wil have to be well informed. They wil 

need to know about changes in science itself and about the climate of opinion in school and the 

community, and they must also be ready to create rather than to present teaching materials. 

When lecturers are preparing physics teachers to enter school laboratories for the first time, 

they have for a decade been able to capture interest by extensive use of project materials. But 

this is becoming less easy since many students wil have followed modem ‘0’ level and ‘A’ level 

280

Teacher education: solar energy 

courses in school and they know something of contemporary apparatus and materials from their 

own experience. Nevertheless, in terms of developing the interest of students in unfamiliar 

subject matter and teaching styles, organizers of initial training programmes have an easier job 

than organizers of in-service work. Much that is old hat to an experienced teacher is new and 

intriguing to a newcomer - and hopes are high on initial training courses. A productive way of 

capitalizing on the optimism and up-to-date knowledge of newcomers and at the same time 

using the wisdom of more experienced teachers is to bring the two together. No better way 

exists than to ask them to devise something new which is an improvement on existing practice. 

A lecturer in a college or department of education now has the chance to influence physics 

teaching in three ways: (i) by recognizing the need for curriculum change and facilitating 

curriculum development at a local level, (ii) by arranging meetings of experienced teachers and 

(iii) by stimulating intending teachers to create new materials and approaches. Many teacher 

trainers do attempt all three of these tasks but it is not usual for the three to be tackled simultaneously, 

as part of a co-ordinated curriculum development/teacher training programme. And yet 

some of the mistrust which teachers have of lecturers working cosily in their colleges away from 

the realities of school would be reduced if a working partnership were developed between lecturer, 

students and teachers. At the present time, good relationships exist between many colleges and 

their neighbouring schools. It is usually focused on students undergoing initial training, but an 

opportunity is often lost. The students practise teaching in school, they prepare their lessons, 

learn to handle apparatus, computers and audio-visual materials. Much of what the students do 

is ephemeral; they do not make a long-lasting input either to the education system as a whole 

or to their practice school. What is lacking is an expectation by experienced teachers that students 

(supported by their lecturers) can provide curriculum materials which improve and expand 

existing resources and which are worth retaining. The lecturers too are reluctant to suggest to 

teachers better ways of tackling themes in physics. They fear that they wil be accused of interference 

or of making unrealistic proposals. If the latter accusation is thought to be valid, then it 

needs to be put to the test. 

In the past ten years, even the newest curricula in physics have been rendered out of date by 

the appearance of two items which have only become prominent in the last few years. One is a 

piece of equipment, the microcomputer; the other is a quite sudden awareness of the overwhelming 

importance of energy to our present and future well-being. The microcomputer merits an 

article of its own, but let it be said that newly qualified physics teachers from Southampton 

University and many other training institutions leave with copies of programs which have been 

developed during the year. In this instance the ‘teacher-trainers-influencing-practice’ ideas are 

restricted to students taking into their first teaching post programs which they have helped to 

create and which are needed in schools. This is a simple and painless way in which in-school 

developments can be stimulated by teacher-trainers via their students. 

ENERGY AND THE SCIENCE CURRICULUM 

Questions of the supply, conversion and use of energy in the last quarter of the twentieth century 

offer perhaps greater opportunities for curriculum development than even the microcomputer. 

Energy can be studied in very many ways, not only in physics courses but also in other science 

courses, in ‘science and society’ options and in history, geography, economics, politics and a 

whole range of school subjects. Historically however, the study of energy has rested firmly in 

the sciences and nowhere more securely than in physics. An economist or geographer wil speak 

more convincingly if he understands the laws of thermodynamics and the nature of energy 

changes and losses. On the other hand, it is becoming clear that a physics programme which 

28 1


concentrates on an academic study of the laws of pure physics is an inadequate preparation for 

decision-making in the real world. The study of energy can be enriched by illustrating physical 

principles by reference to energy conservation and the many ways in which energy can be 

manipulated to reduce the effects of shortages of fossil fuels. 

In the United Kingdom, there can scarcely be a single secondary school without its ‘energy 

conversion kit’. Many still have copper calorimeters with which to study heat exchanges. A11 

include electricity in their courses. There is a wealth of apparatus in schools and a wealth of 

teaching experience connected with energy. This is an excellent foundation on which to build, 

and the fact that students in college or university themselves learned about energy using apparatus 

which is still in use in school means that student and teacher have much in common and that 

innovations can be made from a basis of common knowledge and experience. The other much 

less specific knowledge that is shared is the knowledge of the problems of energy supply and 

distribution which are bound to arise in the very near future. It was in 1973 that oil prices began 

to shoot up. A look at energy supply and consumption statistics [ 1, 21 reveals discontinuities 

in the graphs in or around 1973 and the Club of Rome’s [ 31 assumptions of exponential changes 

are clearly false. The provision of energy for all in the most convenient and appropriate form has 

suddenly become a problem and even the certainties of regular growth and decay have been 

eroded. These factors combine to provide an almost perfect basis for curriculum innovation. 

There is a need for materials which wil help children to become aware of energy issues. There 

is apparatus available for the study of energy. Teachers, students and lecturers alike understand 

the laws of energy conversion. The innovation can be an extension of existing practice and needs 

no radical reshaping of syllabuses or examinations. Studies can be organized in problem form 

and answers can be offered following experimental work or study of resource material. The rest 

of this article is built around a teacher training programme which grew from an awareness that 

the study of energy in school can be extended beyond conventional syllabus material. A dozen 

graduate students (engineers and physicists) were invited to prepare teaching materials and to 

try them out in school. A year later experienced teachers attended in-service courses to consider 

and extend the students’ ideas and to build some apparatus for their schools. Prototype apparatus 

was also built in the university and issued to a number of schools which were asked to comment 

on the strengths and weaknesses of the equipment. 

SOLAR ENERGY 

The students involved in the first development work were attending a one-year course leading to 

a Postgraduate Certificate in Education at Southampton University. The possession of a degree 

meant that their knowledge of physics was sound and that they were technically well-equipped 

to design and handle apparatus. At the time, solar heaters were b,eginning to appear on rooftops 

and studies were being published evaluating performance and cost. Solar heaters heat water; 

traditionally, water in school physics is heated in beakers or calorimeters but the usual ‘heat lost’ 

and ‘heat gained’ calculations can be carried out as easily with solar heated water as with water 

heated by a Bunsen burner. Here was a way of covering an important concept in a context which 

had immediate significance for the boys and girls. Similarly concave mirrors appear in many 

syllabuses. We used big ones in the sunshine instead of tiny ones in a laboratory. Impedance 

matching of electrical supplies and loads is an important topic at more advanced levels. We used 

solar cells, not batteries; they are more interesting and their characteristics change with incident 

radiation. Questions can be asked about solar cells which lead to worthwhile practical investigations 

and which call for quite a depth of understanding to answer convincingly. The concept of 

efficiency is fundamental in the thinking of most engineers and appears in every school physics 

282


course. A solar system adds a new dimension to efficiency studies. It can be measured, but if 

energy is free, efficiency is of no consequence. Or is it? Discussion is not easy to provoke in 

conventional physics lessons, but facing a question like this few classes wil remain silent. At the 

end, they wil be much wiser about efficiency, cost-effectiveness and environmental impact. 

A central tenet of our thinking about physics teaching is that it should be firmly based on 

experience and that practical work which involves an investigation is more valuable than an 

experiment which merely verifies or where the conclusion is implicit in the apparatus or the 

recommended procedures. We also feel that some numerical measurement and calculation add 

strength to a boy or girl’s ability to grasp physical concepts. These educational principles and 

suggestions for worthwhile experiments were discussed with the student teachers. Each was 

invited to choose an experiment using solar energy, to design and build the apparatus for it 

and to put it in a teaching context. The sun, alas, does not always shine in England and every 

student had to have back-up activities if the classes were forced to stay indoors. Some of these 

were parallel experiments. The effects of radiation on coloured surfaces can be studied in sunlight 

or in a laboratory and so can heating and cooling. Some activities were investigations based 

on books and papers. We built up a large collection of popular articles drawn from newspapers 

and magazines, and even on a bad day there was much for the school classes to do. 

The reasons for the production and testing of curricular materials in solar energy are many and 

can be summarized as follows. Sunlight is available almost everywhere, solar energy is in the 

public eye at present and is a potential contributor to local and national energy supplies. Its 

study raises scientific, technical and social questions. These can be considered at an elementary, 

descriptive level, at an early stage of the study of physics and right up to advanced and graduate 

levels. At any stage personal investigations can be undertaken and they can proceed to a level 

of theory and analysis appropriate to the abilities of the investigators. The sun is a source of 

radiant energy across a broad spectrum, -it is a source of heat and light which can substitute for 

conventional sources allowing syllabuses to be extended and enriched without suffering radical 

change. Numerical measurements can be made with solar apparatus and quite easy algebraic 

manipulation enables heat transfer equations to be used to calculate constants and parameters 

of the equipment. Solar energy is a theme par excellence with which to encourage student 

teachers to develop their ideas and to make a positive offering to the educational system. 

THEORY INTO PRACTICE 

Student teachers need pupils to practise on and ours needed to try out their ideas with classes of 

ordinary children in an ordinary school. We approached a secondary comprehensive school in 

which a physics teacher was known to be an enthusiast for alternative technology. Two classes 

totalling fifty children were allocated to us for one afternoon a week for ten weeks. Pupils were 

aged about 14 and were of average and below average ability and motivation. Many of them were 

looking forward to dropping physics for good at the end of the term. Such a class is not an easy 

one to handle, and the boys and girls were taught in small groups so that no student ever had 

more than half a dozen children to work with. A small group enables a student to explore 

relationships and to try out different approaches without risking serious class control problems. 

It also allowed time for them to assess their successes and failures with the experiments and with 

their teaching. In the main, a student stayed with his own piece of equipment throughout the 

term. He was able to refine his presentation continuously as different groups came to him each 

week. On the few occasions when all fifty boys and girls were addressed at the same time, it was 

the writer who did so. 

283


The students were asked to choose and develop an experiment and to prepare a lesson along 

lines which wil be familiar to teacher trainers. They considered what particular benefits the work 

offers (the aims) in terms of the processes of science (definition of problem, skills developed, 

design, choice, reporting, etc.), in terms of the learning of subject matter (absorption of radiation, 

optics, etc.) and in terms of social relevance (contribution to energy in the home, awareness of 

economic significance, etc.). They prepared introductions, presentations and questions. It was 

pointed out that solar experiments often take a long time and that the boys and girls must be 

kept occupied whilst the experiment proceeded. We are not keen on stereotyped worksheets 

which need only a few words to be written or deleted so a variety of activities was called for. 

Wherever possible, frequent involvement with the apparatus was arranged. The best experiments 

were those where adjustments had to be made frequently or where a series of readings (usually 

of temperature and time) were called for. Otherwise boys and girls were asked to draw the 

apparatus, label a diagram, refer to books or offprints, make notes on the experiment or to 

discuss with a teacher what was happening. Table 1 is a list of the experiments attempted. Brief 

notes on some of them are included at the end of this article. 

Most of the experiments worked. One or two did not. The ‘camper’s water heater’ - a concoction 

of hosepipe, polythene and a plastic bucket - resolutely refused to thermosyphon, but the 

level of involvement of the children in constructing and adapting the system fully justified its 

inclusion. At the outset I was sure that the solar oven was badly designed and would never cook 

anything. Again, its very inadequacies challenged many members of the group to improve it. 

The level of invention on the part of the children was remarkably high and the feeling of success 

when an egg was finally cooked justified the time that had been taken. The washing-up bowl 

mirrors (see below) leaked and the radius of curvature of the surface slowly increased. But this 

was turned to good effect. As the focal length changed, so the children had to increase the 

distance between the mirror and the can that was being heated. They learned in an active way 

that the curvature and focal length are intimately connected. We still have not solved the sealing 

problem, but the mirror is so good that it is one of our greatest successes - and the vacuum 

holds long enough for the mirror to be used throughout a double period. 

Overall the attempt to introduce a practical study of solar energy into a school curriculum 

was entirely successful. The attitudes of the university students were changed and many of them 

have continued to work with solar energy in their own schools. The children enjoyed working 

in the sunshine at problems which had a practical application. School staff from many different 

disciplines stopped to have a word about progress and we even picked up one very enthusiastic 

girl who should have been at lessons elsewhere. One big problem which arose was storage of 

apparatus. Space is not plentiful in school laboratories. The apparatus could not be left outside 

overnight for fear of damage and the temporary storage in the school hall was unsatisfactory 

as a long-term measure. As our apparatus has developed, so it has got smaller. There is no need 

to have many square metres of surface and many litres of water. Effects are often observed more 

quickly on a smaller scale and the storage problem is eased. The children we worked with were 

not examination candidates in physics so we were free to use time as we wished, unrestricted 

by demands to get through a syllabus. Even so, we felt that the work related so well to ‘0’ level 

and CSE examination syllabuses that time in the sunshine for even these candidates would be 

well spent. 

A further problem was pointed out by the students. Working with four or five children is easy. 

The organization of a whole class in the hands of one teacher would be much more difficult. 

The distribution and erection of apparatus would need to be very carefully controlled and the 

scheduling of work would need to depend far less on the continuous presence of a teacher. 

Perhaps more detailed worksheets would have to be written or the variety of activities would 

284


need to be curtailed. Experienced teachers working with whole classes were needed to look 

into this. 

EXTENSION TO IN-SERVICE EDUCATION 

The experiment with student teachers demonstrated that a study of solar energy in school is 

worthwhile, but that practical problems remained. Prototype apparatus had been built which 

needed refinement and production in larger quantities. Laboratory suppliers are now supplying 

some solar apparatus, but it is much cheaper to build it oneself and a teacher’s own preferences 

can be incorporated into home-made apparatus. Three different needs of experienced teachers 

were recognized. They need to know more about the whole energy supply question and the 

economic and technical issues behind it. They need apparatus with which to work and they need 

help in organizing lessons outdoors. Two evening courses were arranged for teachers each lasting 

ten weeks. The first was a series of lecture-demonstrations covering not only the theory and 

practice of small-scale energy provision, mainly solar and wind, but also discussion of the ways 

in which the study of energy in school can be incorporated into and extended from existing work. 

The second course was entitled ‘Build Your Own Solar Collector’ and a group of teachers 

attended a purely practical course in which materials and tools were provided so that teachers 

could take collectors back to their schools. At the same time, they were introduced to other solar 

devices. 

The original work had shown that more quantitative investigations could be carried out if there 

were an instrument which could measure solar radiation density. A commercial solar pyranometer 

was purchased as a standard and a much cheaper version was designed and built. The ability to 

measure incident radiation in watts per square metre made a whole range of new calculations 

possible. The calculation of efficiencies was now easy. We also needed a cheap, robust thermometer. 

Mercury in glass thermometers are becoming too expensive for schools to provide and 

they proved too fragile for the outdoor environment. As their price falls so electronic thermometers 

are becoming a better buy for class use. To keep costs down, we have designed and built 

our own electronic thermometer for use outdoors. We also realized that if children were to make 

the most of their energy studies, they needed more data. A collection of data sheets was therefore 

prepared [4]. The facts, figures and graphs contained therein were sufficient to permit 

advanced study and calculations to be performed and enough information was given to help in 

the design and construction of working installations. There is still much to be done and we have 

only started on a widespread dissemination of our ideas. At the time of writing, six sets of solar 

apparatus are in schools for evaluation by teachers, occasional meetings of teachers are being 

arranged and visits are being made to schools. The apparatus and teaching materials are likely to 

be adapted and developed continuously and we are confident that the interaction of university 

staff, experienced teachers and students-in-training wil continue ‘into the foreseeable future and 

that a study of energy covering far more than the physics of the 16th to 19th centuries wil 

slowly come to be looked upon as an essential component of science courses. 

REFERENCES 

1. 

2. 

ION, D.C. Availability of World Energy Resources. London, Graham & Trotman, 1980. 

SINGER, S. Fred (Introd. by). Energy: Readings from Scientific American. San Francisco, Calif., W.H. 

Freeman, 1979. 

285


3. 

4. 

The Limits to Growth: A Report for the Club of Rome’s Project on the Predicament of Mankind, by D.H. 

MEADOWS et al. New York, Universe Books, 1972. 

Energy Data Sheets, by Cliff DAY. SSTF, Southampton University, 1981. 

A SELECTION OF SOLAR EXPERIMENTS 

Outlines of five examples of solar equipment and experiments are presented below. The construction 

of apparatus is usually self-evident and only the briefest of hints are given. In the 

same way, most physics teachers wil see the possibilities in the proposed experiments and 

investigations and will be able to extend and improve on the ideas suggested. 

TABLE 1. Apparatus and experiments 

Apparatus 

Illustrating Physical Principles 

Coloured aluminium plates 

Absorbing power of coloured surfaces 

* Solar cushions Absorbing power of coloured surfaces 

Steam engine 

Energy conversion 

Solar still 

Evaporation 

Survivor’s still 

Evaporation 

Fresnel lens 

Converging light and heat 

* Washbowl mirror Focusing by concave mirror 

Bicycle wheel mirror 

Focusing by concave mirror 

* Headlamp array Heating, effect of colours, insulation 

Camper’s water heater 

Convection 

Flat plate heater 

Heating, convection, efficiency 

(i) thermosyphon 

* (ii) pumped 

Solar oven 

Heating, efficiency 

* Solar cells Internal resistance, impedance, matching, efficiency. 

*Brief descriptions of these items are given at the end of this article. Outlines of the others may be obtained from the author at 

the Department of Education, University of Southampton, Southampton, SO9 5NH, United Kingdom. 

Headlamp heaters 

Made from 

Aircraft landing light reflectors 

(car headlamp reflectors wil do) 

Boiling tubes in Terry clips 

Wooden board 

Thermometers (The photograph, figure 1, 

shows the board wired for an electronic 

thermometer.) 

Construe tion 

Holes are cut in the board and the reflectors are stuck in position. The Terry clips are screwed to 

286


the board so that they hold the boiling tubes at the foci of the reflectors. An adjustable leg at 

the back allows the plane of the board to be maintained at right angles to the sun’s rays. 

Experiments 

The reflectors in sunlight act as six identical heat sources. This enables thermal properties of 

materials to be compared simultaneously. A straightforward experiment is to put 20, 40, 60, 

80, 100 cm3 of water in each of the test tubes, to leave them for about 15 minutes and to note 

the different changes in temperature. An extension of this is to use equal masses of different 

liquids, for example, kerosene or alcohol or even to use the same mass of iron filings, zinc turnings 

and water as an introduction to specific heat capacity. A popular experiment is to compare 

the temperature rises of different coloured waters, clear, blackened (with indian ink or aquadag) 

red, green, etc. (use poster paints). 

Investigations on the effect of covers or diffusers over the reflectors can also be carried out. 

Figure 1. Reflector array with electronic thermometer. 

287


Solar cushions 

Made from 

A range of impermeable materials: 

black polythene, silver reflective 

mylar, transparent polythene, 

golden mylar, etc. 

Waterproof sticky tape 

Plastic tube, rubber bungs 

Thermometers 

Construction 

25 cm squares of materials are stuck together with waterproof tape in different combinations of 

upper and lower surface; black/black, transparent/silver, clear/black, etc. (figure 2). A short 

length of plastic tubing is fitted to enable the ‘cushions’ to be filled., 

Experiments 

A litre of water is poured into each ‘cushion’. Its temperature is taken and the cushions are laid 

flat in the sunlight for half an hour. Temperatures reached are compared to find the best combination. 

This experiment can be varied by using larger or smaller masses of water, by changing the 

time, by insulating the underside and by putting the filled cushions in large plastic bags, blowing 

them up and sealing them. Or put the ‘cushions’ under gardeners’ cloches. 

Figure 2. Solar cushions. 

288


A Pumped FlatPla te Heater 

Made from 

Plastic horticultural tray 

Used aluminium photo-litho plate 

(from a scrapyard) 

1 2v windscreen washer conversion kit 

Plastic guttering 

Copper pipe 

Window glass 

Plastic tubing, paint, fibreglass 

insulation, etc. 

Construction 

Small holes are drilled about 1 cm apart in the copper pipe. The tray is lined with insulation and 

the aluminium sheet (painted black) is fixed inside it. The pipe with holes is mounted at the top 

so that water leaves the pipe and trickles down the black surface into the guttering at the bottom, 

then into the reservoir whence it is recirculated via plastic tubing. Glass (one or two sheets) is 

held in place with expandable curtain wire. 

Few details are given since there are many ways of arranging the flow. The photograph (figure 

3) shows one way. An adjustable ‘leg’ at the back allows the heater to be angled to face the sun. 

Figure 3. Pumped flat plate heater with cover removed. 

289


Experiments 

Power input from the sun can be calculated by measuring the mass of water and the temperature 

rise. (But don’t forget the electrical input.) This apparatus enables boys and girls to change a wide 

range of conditions and to study the effects. For example: 

Rate of flow 

Mass of water in the stream 

Double or single glazed (or no glazing) 

Angle to the sun 

Time of day 

Separation of holes in the pipe 

etc. 

Students can suggest a design and an on-off schedule which will enable the heater to (a) work 

most efficiently (b) extract the maximum energy from the sun. 

Figure 4. Wash-bowl mirror. 

290


A Washing-up Bowl Mirror 

Made from 

Plastic washing-up bowl 

Valve cut from an old cycle tube 

Reflecting mylar film 

(sold as rescue blankets in camping shops) 

Adhesive and heavy duty sticky tape 

Rubber tubing and clip 

Construction 

Drill a hole in the bowl, push the cycle valve through from the inside and stick it to the bowl. 

Loosely lay a circle of mylar over the rim of the bowl and fix it in place with heavy duty sticky 

tape. We have not yet found perfect sealants but Araldite for the valve and wide plastic tape 

for the rim perform adequately. Remove the valve inner, fix the rubber tubing and the clip and 

gently remove air from the bowl. This can be done by sucking.with the mouth (hard work!) or 

by applying a vacuum pump. The mylar assumes a spherical form and acts as a concave mirror 

of remarkably high quality (figure 4). 

Figure 5. Fresnel lenses. 

29 1


Experiments 

Real and virtual images can be obtained. 

The focal length can be measured. 

By reflecting sunlight onto a blackened soft drinks can of water the rate of heat absorbed can 

be discovered. (We boiled the water and made tea.) If a solar pyranometer is available the energy 

falling on the mirror can be compared with the energy absorbed by the can in the same time and 

hence the efficiency of the system can be calculated. 

Note 

These experiments can also be carried out with a Fresnel lens removed from an unwanted overhead 

projector (figure 5). 

Figure 6. Solar cells. 

292


Solar cells 

Apparatus 

Solar cells must be bought commercially. 

The bigger and the greater the number 

the better. 

3V high impedance voltmeter 

1A ammeter 

(These ranges are satisfactory for up to 

20 cm2 of cells. Larger or smaller areas 

may need different meters.) 

Low power electric motor 

Coloured filters 

Resistance box 

Solar pyranometer 

Experiments 

Less able pupils benefit from connecting the motor to the cells and trying it in sunshine and in 

shade. Cells can be connected in series or in parallel, singly or in groups (figure 6). The effect of 

coloured filters can be examined, with the motor or with the cells shortcircuited by the ammeter. 

Responsible children can try to power a transistor radio by sunshine. 

The range of more advanced experiments which can be performed is extensive. Only hints are 

given here, teachers qualified to handle the concepts involved wil be able to provide the experimental 

and mathematical detail for themselves. Some more advanced investigations: (i) maximum 

power output, (ii) voltage/current characteristics under different loads and different light intensities, 

(iii) the effective internal resistance, (iv) the reverse resistance of the cells, (v) power losses 

under load and in darkness when connected to a storage battery, etc. 

The cost of photovoltaic cell installations must drop by almost an order of magnitude for 

universally competitive electricity to be produced. However, a study of the economics and 

possible uses of cells is interesting and valuable. 

293

Part V 

From Micro-computers to Low-cost 

Equipment

Micro-computers as laboratory instruments 

Microcomputers in the laboratory 

J.W. LAYMAN. 

Microcomputers or personal computers are becoming so inexpensive that many parents feel that 

their children wil be deprived of one of the major skills needed for the future if they do not 

grow up using such devices. Parents in turn are pressuring schools to incorporate them into their 

teaching, but this frequently occurs in mathematics or business areas rather than in science. These 

devices have their greatest potential in science because they can allow students regularly to sample 

features of the real world in time scales not amenable to the stopwatch, the mercury thermometer, 

or the ticker-tape timer. 

A prime example that fits in well with the theme ‘the teaching of energy,’ would be the ability 

to study the properties of a solar collector using a microcomputer to obtain and display successive 

temperature-time graphs as the parameters of the solar collector are changed. This is the introductory 

experiment in the American Association of Physics Teachers (AAPT) one-day workshop An 

Introduction to Microcomputers as Laboratory Instruments [ 1 ]. A small (1 2 cm X 12 cm X 4 cm) 

chamber with a clear plastic cover illuminated by a light source contains a flat aluminium plate, 

black on one side, shiny on the other, fitted with an AD590 temperature-sensing integrated 

circuit that allows a current of 1pA/K to pass through it. This current is translated into a voltage 

which in turn can be sensed by the laboratory interface circuitry and logged in the microcomputer 

memory as a data point (a temperature). The AD590 is a transducer providing analog information 

about temperature to a laboratory interface board which provides analog to digital and digital to 

analog signal conversion. The digital temperature information is finally stored in the microcomputer 

which also provides the program to control the collection and display of the data. An 

oscilloscope, which serves as the display device, is the final part; through program control in the 

microcomputer, it can display a graph of temperature versus time. 

A microcomputer-based system allows students to run a succession of experiments: black 

collector up, shiny collector up; using a glass cover, a plastic cover, or no cover; and with varying 

intensities, distances, or angles of the light source. The microcomputer not only takes the drudgery 

out of data collection, but after data collection, these successive temperature/time curves may be 

displayed on the oscilloscope showing clearly the changes in the heating or cooling behaviour 

associated with changing the various collector parameters. The whole experiment is designed to 

aliow the graph appearing on the oscilloscope to be generated as the data are gathered, in other 

297


words, in real time. Students can observe immediate changes if an ice cube is placed on the 

collector plate. One of the greatest contributions to the intuitive understanding of the temperature 

changes in such a system is to see, in real time, the asymptotic behaviour of the temperature 

of the chamber as it approaches its maximum value, or returns to room temperature. Students 

could also build more complex collectors and monitor temperatures in a number of locations. 

Their basic challenge would be to modify the transducer system and write additional program 

steps (software). 

A second example of the value of having the patience and persistence of a microcomputerbased 

laboratory instrument would be using it to monitor the period of a pendulum. In most 

laboratory experiments, students are asked to determine carefully the period of a pendulum by 

counting a number of swings and measuring the total time period for that number. Using the 

period and the length of the pendulum, the value of g may be found. With the microcomputerbased 

instrument, each period of the pendulum can be recorded over many swings, clearly showing 

any decay in the period if it occurs with time. One can then answer such questions as: does 

the period of the swing actually depend on the amplitude or ‘small angle’? or can air resistance 

play a role if the surface character of the mass is changed? or does mass really play a role? When a 

microcomputer is used as a data storage device, 256 separate periods or more may easily be 

recorded and retrieved for later study. A student who is able to test intuitions about the effect 

of mass, the angle of swings, and the effects of air resistance, as well as determine g, certainly 

has had a thorough introduction to the pendulum. 

What is required to do this kind of measurement and why would we choose a microcomputerbased 

instrument? Building on the pendulum example, the first element required would be a 

transducer which would be a light source (infra-red diode), a light detector and simple electronics 

to produce an output voltage proportional to the light level. The second element would be an 

interface between the transducer and the microcomputer so that the analog signal from the 

transducer can be converted to digital information that the microcomputer can deal with. This 

is called a laboratory interface board. The third element, and indeed the newest element, is the 

microcomputer itself. It has the capability of following a stored set of instructions called a 

program, sometimes called software, that controls the operation of the whole system. It can bring 

about the analog to digital conversion, provide the timing for the system operation, provide the 

time base for storing the successive individual periods of the pendulum and provide the means for 

retrieving the stored data for student analysis. The final element would be an output device to 

read out or display the measured periods of the pendulum. The cost for a single board microcomputer 

(KIM I) [21, a Laboratory Interface Board, a power supply and a transducer and its 

associated electronics would be less than $600 (1 981 price). 

The power of the microcomputer-based laboratory approach lies in the fact that it will not 

only monitor and record successive periods of a pendulum, or the successive temperatures of a 

solar collector, but any physical process or processes amenable to general instrumentation. Thus 

the same basic laboratory instrument can serve a wide variety of experiments. All that is required 

is to change the transducer and the program which runs the system. In the past, it meant changing 

devices entirely, which required having a variety of separate and costly instruments. 

A number of other laboratory applications have been developed for the AAPT workshop. 

These include the ability to move a photo-diode attached to a linear potentiometer across an 

interference pattern and have the amplitude versus position graph appear on the oscilloscope. 

The patterns can be quickly changed and new graphs produced. The detector could be changed 

to allow studies of infra-red, ultraviolet, or ultrasonic interference patterns where the pattern 

itself would not be visible. Temperature sensors may be placed along a conductor to show heat 

transfer and thermal gradients, and to measure R values of insulating materials, etc. An optical 

298

Microcomputers in the laboratory 

analogue to the old ticker-tape timer can be used to allow simultaneous display of the position, 

velocity and acceleration of a moving mass. This illustrates the ability of the microcomputer to 

process data and display the results as the data are acquired. 

With slightly more sophisticated electronics, one can do pulse height analysis and radioactive 

half-life experiments, study rotational dynamics and study various transient phenomena by 

using the system to capture a brief signal and then displaying the signal as one would with a much 

more expensive storage oscilloscope. 

What general mechanism might make this all feasible for the average physics teacher? A small 

group of teachers within AAPT proposed that a workshop be developed. With AAPT support 

and in collaboration with the Technical Education Research Center a one-day workshop was 

designed to introduce physics teachers to the microcomputer as a laboratory device. The equipment 

developed for the workshop included each of the elements mentioned earlier: a single board 

microcomputer; a laboratory interface board containing the circuits for analog to digital and 

digital to analog conversion; a set of transducers and their analog circuitry; and most important, 

a read-only memory chip (ROM) resident on the laboratory interface board which contained the 

program needed to carry out the experiment with the solar collector as well as all other programs 

used in the workshop to introduce teachers to the microcomputer as a laboratory instrument. 

Workshops or special courses are needed because most teachers received their training when 

none of this technology was available, and at present the most commonly observed applications 

of microcomputers do not involve interfacing with the real world in a laboratory setting. Teachers 

must be given opportunities to judge for themselves whether such devices can enrich their 

student’s understanding of physics. 

All comments up to this point have referred to a specialized system designed to utilize a simple 

single board microcomputer, a laboratory interface board, transducers and an output device. 

What about the more complex microcomputers such as the Apple IT, BBC, OS1 Challenger, 

Radio Shack TRS-80 or Sinclair, that offer instant and sometimes colourful graphics, that speak 

a high level language such as BASIC and are purchased ready to plug in and use? What role can 

these play in the laboratory? One use made of these personal computers is to play games, a 

feature of which many physics teachers may be critical. It turns out, however, that the game 

paddles which allow the user to control features of the game are in fact connected to built-in 

analog to digital converters. In an Apple 11, a game paddle can be replaced by a thermistor whose 

resistance is proportional to temperature, so that with a simple program the student can obtain a 

real-time graph of temperature versus time and even superimpose this on a graph background. 

The cost of the thermistor, its connecting wire, and connecting pins is really quite low, allowing 

a teacher to convert a machine that might have been used simply to solve equations and plot 

standard functions in the maths or science class, into an active laboratory device; one with a 

large memory and built in programs for producing real-time graphs of physical phenomenon. The 

thermistor is an example of a device whose resistance is not linearly related to its temperature. 

Thus, to plot the actual temperature, the computer must first solve the nonlinear relationship 

between resistance and temperature, a task which it does easily. 

Many of these microcomputers are also designed to produce musical tones as one output 

function. The device which produces the tone is actually a digital to analog converter, which was 

again provided on the laboratory interface board. So one can see that the more costly microcomputers 

may be used as laboratory devices with input and output interfacing capabilities if 

the teacher gains enough experience through the mechanism of a workshop or a course to use it. 

I must apologize to the teachers who read this discussion and find the vocabulary quite new 

and the devices not available in their own countries, and who have had no opportunity to gain 

299


personal experience with a microcomputer. A most comprehensive and semi-technical description 

of microcomputers and their role in the laboratory was presented in an article in The Physics 

Teacher by Robert Tinker of TERK [4] 

- 

Debate will continue as to the role of microcomputers in the classroom and laboratory, 

especially in introductory courses. When teachers realize that these devices can extend in an 

intuitive manner the ability of students in question and monitor physical systems as illustrated 

by the solar collector and pendulum examples, they wil become more widely accepted. This 

can not occur, however, until a greater effort is made to introduce physics teachers to these 

capabilities and offer them the skills to use microcomputers in their own labs and classrooms. 

REFERENCES 

1. 

2. 

3. 

4. 

For more information write to The American Association of Physics Teachers, Executive Office, Graduate 

Physics Building, SUNY at Stony Brook, Stony Brook, N.Y. 11794, United States. 

KIM was manufactured by MOSTechnology, but is now out of production. The new AAPT Workshop version 

wil use SYM. 

Technical Education Research Center, Cambridge, Mass. 02138, United States. 

TINKER, R. Microcomputers in the Teaching Lab. The Physics Teacher. Vol. 19, No. 2, February 1981, 

pp. 94-105. 

See also: 

0 Microelectronics in Education: Control Applications. Conference report published by Brighton Technical 

College, Brighton, United Kingdom, 1981. 

Microprocessors and School Physics. Physics Education, Vol. 16, No. 3, May 1981, pp. 136-51. 

SPARKS, R.A. Microprocessors in Science Teaching. London, Hutchinson Education, 1982. 

SUMMERS, M.K. Microprocessors in the curriculum and the classroom. Computer Education, Vol. 31, NO. 1, 

February 1979,pp. 9-14. 

Reference should also be made to the Harris Data Memory, a device which permits the recording of up to 

512 experimental results in the form of electrical voltages at rates of from 3 per hour to 1000 per second. 

These can then be replayed into a chart recorder, a meter or an oscilloscope at any of the rates mentioned. 

This allows the user to slow down rapidly changing values or to speed up very slow ones. Details from Philip 

Harris, Ltd., Lynn House, Shenstone, WS14 OEE, United Kingdom. 

300

A solar cooker 

How to construct a solar cooker 

PHYSICS WORKGROUP OF THE SCIENCE EDUCATION CENTER, UNIVERSITY OF THE 

PHILIPPINES~ 

This activity, which was designed for grade 9 or 10, is estimated to take ten hours to perform. 

It is best done after the students have studied temperature, reflection at a plane mirror, the 

modes of heat transfer, heat capacity and conductivity. 

CONCEPTS AND SKILLS TAUGHT 

1. Paper is a good insulator. Crumpled up, it prevents convection of air inside a box. 

2. Tripled layer plastic can insulate the cooking area of a box. Low energy radiation cannot 

pass through plastic. 

3. Aluminium foil or mirror reflects energy to the cooking area of the box. The aluminium 

foil also insulates the cooking area. 

4. Warm air tends to rise above sinking cold air. 

5. Constructing a solar cooker. 

OBJECTIVES 

1. To construct a solar cooker and describe its important parts. 

2. To compare the temperature inside and outside the solar cooker. 

3. To illustrate the modes of energy transfer using the solar cooker. 

4. To cook eggs using the solar cooker. 

5. To state the factors affecting the use of a solar cooker. 

1. In association with the Bureau of Energy Development of the Ministry of Energy. 

301


MATERIALS 

a. Outer Box, A 

large carton, about 64 cm X 42 cm X 42 cm 

tape or paste 

blade or pair of scissors 

ruler 

pencil 

b. Inner Box, B 

small carton about 58 cm X 30 cm X 32 cm 

plastic sheet about 64 cm X 34 cm X 1 mm 

7 card sheets 30 cm X 6 c m 

aluminium foil 

blade or pair of scissors 

tape or paste (glue) 

ruler 

pencil 

carbon paper (as used in typewriting) 

c. Door (Box C) 

card sheet about 30 cm X 30 c m 

card sheet about 29.5 c m X 29.5 cm 

2 card sheets about 59 cm X 6 c m 

glue 


dry newspapers 

masking tape 

hammer 

2 nails about 3 cm long 

2 pieces wood about 2 cm X 3 cm X 12 cm 

d. Reflector 

wood, 58 cm X 6 cm X 1 cm 

cardboard, 58 cm X 30 cm 

cardboard, 58 cm X 28 cm 

aluminium foil, 60 cm X 32 cm 

paste or tape 

e. Insulation 

4 long card sheets about 64 cm X 6 cm 

4 short card sheets about 30 cm X 6 cm 

plastic sheet, 70 cm X 45 cm 

plastic sheet, 76 cm X 48 cm 

old newspapers 

masking tape 

f. For cooking 

2 black painted cans, about 20 cm X 20 cm X 5 cm 

2 thermometers 

measuring cylinder 

5 chicken eggs 

600 ml water 

302


PREPARATION AND SUBSTITUTES FOR MATERIALS 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

If there are no big boxes available, 

(a) use old newspapers to make papier mache and form a box from them. 

(b) dismantle small boxes and paste or sew the pieces together to form a bigger one. 

(c) form any low conductivity material into a box. 

If black paint is available, it can be a substitute for the carbon paper. 

For a more durable cooker, aluminium sheet can be used in place of aluminium foil, provided 

the bottom part is painted black. 

Mirror can be used instead of aluminium foil as reflector. 

Gauge 10 transparent plastic sheet can be used if gauge 12 is not available. 

The big carton should be at least 6 cm longer and wider than the small box for better insulation. 

The greater the absorption area of the box, the more energy wil be collected. A 0.6 m2 area 

or bigger gives a better efficiency. Generally, the lower the height of the cooking area, the 

higher the temperature that wil be attained. 

The plastic sheet should be stretched to avoid convection. 

PROCEDURE AND QUESTIONS 

A. To make the outer box, A 

a. Cut and construct the outer box A from a large carton according to the dimensions 

given in figure 1. 

The final box has an open top and a 30 cm square hole cut in the taller end. 

Note that the angle shown on the figure is equal to the approximate latitude of the 

Philippines. If constructing the cooker elsewhere, the design must be modified so that this 

angle is equal to the local latitude. 

Figure 1. 

3 03


B. To make the inner box, B 

a. Remove one side of the small carton. (See figure 2.) 

b. Cut the carton and construct the box according to the dimensions given in figure 2. 

c. Paste the seven 30 cm X 6 cm card sheets on top of one another until about 2 cm thick. 

Let it dry. 

d. Tape this thick card sheet to form the upper edge of the inner box as shown in figure 2. 

n 

Figure 2. 

e. 

f. 

g. 

Paste aluminium foil on the floor, walls and all surfaces inside and outside box B. Make 

sure there are no gaps at the edges of the f6il where air can pass through. 

Q.1 Why is aluminium foil pasted on all surfaces of box B? 

Paste carbon paper (black side up) to the floor and inside walls of box B. Let it dry. This 

is your cooking space. 

Q.2 What is the purpose of pasting the carbon paper to the inside of the cooking space? 

Cover the top with the plastic sheet and tape it to the sides. 

Q.3 Why should box B be covered with plastic sheet? 

C. To make the door 

304 

a. Centre the 30 X 30 cm card sheet between the two pieces of wood as shown in figure 3 

and nail the sandwich together. The wood serves as a handle. 

b. Construct a box out of the remaining card sheets, Paste aluminium foil lining inside it.


c. Fill the box in (b) with crumpled newspapers. Compress. 

d. Cover the box with the card sheet of (a) and secure with tape. 

e. Paste aluminium foil outside the box (except the front side with the handle). (See figure 3.) 


\ 

Figure 3. 

D. Making the reflector 

a. Construct a triangular stand out of the pieces of cardboard using dimensions in figure 4. 

b. Paste or tape the aluminium foil on side of the triangular stand. Do not use crumpled 

aluminium foil. (See figure 4.) 

c. Insert the piece of wood at the base of the stand. 

Q.4 What is the function of the reflector in the cooker? 


k- 58cm-/ 

Figure 4. 

305


E. Assembling the cooker 

a. Fill the floor of box A with crumpled newspapers to a depth of about 7 cm. Compress. 

b. Place box B on top of the crumpled newspapers. See to it that the spaces in between the 

boxes are roughly equal all round. 

C. Fill the spaces in between the boxes with crumpled newspapers. Compress. 

Q.5 Why should the spaces between the boxes be filled with crumpled newspapers? 

d. Cover the newspapers with 2 long and 2 short card sheets. 

e. 

f. 

g. 

h. 

1. 

j. 

Compress so these sheets are approximately ?h. cm below the top of box A. Tape them 

to the walls of box A. 

Place the smaller plastic sheet on top of the inner box B. (This is the second layer of 

plastic sheet.) Stretch the plastic to avoid convection. Tape it to the sides. 

Place the remaining card sheets on top of the plastic sheet in (0, leaving the cooking 

space uncovered. Tape it to the sides of box A. 

Cover outer box A with the bigger plastic sheet and tape it to the outer side. 

Carefully fit the door to the cooker. Be sure that the box is sealed. 

Attach the reflector to the box by taping it lengthwise to the box. (See figure 5.) This is 

your box type solar oven. 

plast ,IC 

sheet 

box 

aluminium foilZ 

cardboard 

Figure 5. 

Q.6 What are the main parts of the solar cooker? 

F. Place the solar cooker you have just constructed on a sunny area. 

G. Orient the cooker so that the lower end is at the south I while the taller end is at the north. 

1. Editor’s note: The cooker was designed for use in the Northern hemisphere. The ends should be interchanged South of the 

Equator. 

306


Let the reflector face the sun. 

Q. 7 At what timeof the day and in what months of the year can you best use a solar cooker? 

Q.8 Which people do you think will gain most in using solar cooker, those from the North 

pole? South pole? or from the equator? 

H. Bore a 0.6 cm diameter hole in the lids of the cans. Place about 300 ml of water in each can 

and replace the lids. Next place a thermometer in each can. 

I. Place one can inside the cooker and the other outside. 

J. Adjust the reflector so that sunlight is reflected on to the can. 

K. Record the temperature readings every 15 minutes. See to it that the reflection of sunlight 

is focused on the can every time you take a reading. 

Q.9 How do wind and clouds affect solar cooking? 

L. Record your data in a table similar to table 1. 

L 

Time Temperature of water Temperature of water Weather condition 

inside the cooker outside the cooker (cloudy, sunny, windy) 

M. When the water reaches boiling point, it can be used for cooking. 

Q. 10 How much energy was used in boiling the water? 

Where did the energy come from? Hint: Use H = Cm A t 

N. Carefully remove the can and thermometer inside the cooker and open it. Add about 50 ml 

of tap water and 5 eggs. Take the thermometer away and replace the lid tightly. 

0. Place the can with eggs inside the cooker. 

P. After one hour, remove and taste the eggs. 

307


Teaching Hints: 

1. The solar cooker is best used between about one hour before and one hour after the sun 

crosses the meridian during the summer and/or dry season months. 

2. Aluminium foil is pasted in all sides of Box B to prevent heat losses, reflect radiation to the 

cooking area, and to prevent radiation outside the box. 

3. The solar cooker can be placed outside as soon as the sun shines to store heat inside. 

4. Twelve eggs can be cooked in the can with 400 ml water in one and a half hours, between 

1100 and 1300 hours. The eggs should be in a single layer. 

Sample Data for Solar Cooker 

I. Boiling Water 

Time 

Temperature of 300 ml 

of water outside the cooker 

("C) 


of water inside the cooker 

("C) 

Weather 

Condition 

09.30 

09.45 

10 .oo 

10.15 

10.30 

10.45 

37 

37 

39 

40 

41 

41 

37 

58 

84 

94 

100 

100 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

I1 Boiling Eggs 

Time 

09.30 

09.45 

10.00 

10.15 

10.30 

10.45 

1 1 .oo 

11.15 

11.30 

11.45 

12.00 

eggs were cooked at 11.15 a.m. 

Temperature of eggs and 300 ml 

of water inside the cooker 

("C) 

30 

34 

35 

37 

45 

50 

65 

75 

82 

90 

100 


of water outside the cooker 

("C) 

30 

32 

32 

32 

35 

37 

39 

41 

41 

42 

42.5 

Weather 

Condition 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

sunny 

308

String and tape experiments 

String and sticky-tape experiments 

R.D. EDGE. 

Physics can be fun, but many students today believe that it is something which comes out of a 

textbook, redolent of equations and examples divorced from reality. Part of the problem arises 

because of the cost of experimental equipment, both for demonstrations and student laboratory 

work. This is seen not merely in developing countries, which have no heritage of experimental 

physics, but also in industrialized nations where experimental physics plays less and less of a role 

in the curriculum, on the grounds that there is not enough time for it if all the subject matter is 

to be covered. Although this may not be important for dedicated physics students, it is unfortunate 

for those less able, in that physical concepts are more deeply embedded in our consciousness 

if they can be reinforced by experiment. 

Another aspect of the problem arises from the vicarious age in which we live, where children 

sit glued to the television, experiencing remotely and through others rather than going out and 

learning about the world first hand. Physics is an experimental science, and only by doing ‘handson’ 

experiments - messing about with the equipment - can you get a feel for it. One difficulty 

is that most physics gear sold to schools is too expensive to allow students to work with it alone, 

and to have the teacher hovering over one can be quite inhibiting. 

To avoid this problem, the equipment must either be very strong, unbreakable in fact, or so 

cheap it can be replaced at little cost. 

The following experiments were put together to see what could be done with the simplest, 

least expensive materials. The equipment can all be purchased at the nearest store - not even a 

seconds watch is required (although it would be a help), nor are you exhorted to ‘go down to 

the junk yard and pick up a 2000 volt transformer’ as is done in some books aiming at economy. 

In spite of their simple nature, the experiments are quite meaningful, and demonstrate fundamental 

physical laws in a practical way. 

EQUIPMENT 

The experiments involve only common rubber bands (about 7.5 cm unstretched, if available), 

cellulose tape (the cheapest, clear 1 cm kind), regular paper clips, Styrofoam or paper cups, 

309


string, drinking straws (plastic, and preferably translucent), glass marbles, paper, a 30 cm ruler 

with a channel down the centre (provided to prevent the pencil rolling off the desk), coins, a 

pencil and scissors. It is a good idea to collect these simple items and keep them in a box, so that 

they are easily available. In addition, the magnetism experiments require a small magnet of any 

kind, and the electricity experiments some aluminium foil, and a battery or power supply. 

Here is a check list of the equipment mentioned above: 

paper clips 

clear cellulose tape (about 12 mm) 

rubber bands (7.5 cm X 2 mm) 

paper or plastic cups 

straws 

marbles 

paper 

ruler 

string 

pencil 

scissors 

coins 

It is common knowledge that whereas with history, geography and many other subjects, the 

first course is the easiest, the first physics course may well be the most difficult in that it depends 

on understanding new concepts, not merely facts. Concrete examples put in front of one can be 

mentally very satisfying, and to students in developing countries, who have little contact with the 

modern industrial world, this is even more important. It is well known to psychologists that 

students pass through a phase where they comprehend concrete examples before they can deal 

with abstract reasoning. Therefore, most of our experiments provide two approaches. The first 

is qualitative, to give students who are more at home with concrete concepts, a feel of what we 

are talking about. The second is quantitative, so that those who have passed beyond this stage 

may understand fully the physics involved. 

Students have generally absorbed the most elementary concepts of physics before they reach 

the stage of this article, but it might be useful to recall them. The idea of quantity is one not 

immediately evident to youngsters. If you take a sheet of paper such as this page and cut it into 

ten long strips, joining them together, a youngster wil probably think there is more of it, because 

it is so long. The fact that the area is independent of the length of an object (or correspondingly 

the volume of, say, a piece of clay, does not depend on whether it is long and thin or short and 

fat) requires considerable thought - it is not self evident, though we may think so. The area of 

the paper does not change when we cut it up, however we arrange the pieces. The next step, 

that the area is the product of two lengths, requires more abstract thinking. It is before and as 

the student enters this abstract phase that hands-on experiments prove most useful. 

The Experiments below provide a diverse selection of those we have developed. Some of them 

have been published in articles in the journal, The Physics Teacher [I]. Employing games to 

perform experimental physics seems to be a new idea. 

The object of this article is to encourage the reader to get up, go to the larder or nearby store, 

acquire the materials required and try the experiments. 

Couples and torque 

As an example, the first experiment demonstrates an application of couples and torque. 

310

~ 

~ 


It requires: Two Styrofoam or paper cups, sticky tapes and string. 

The bottoms of the two cups are attached together, as shown in figure la. The string is taped 

to the joint, and wrapped around it several times. Now, place the cups on the floor horizontally, 

hold the string level with the floor, and pull (figure lb). Which way do the cups move? Hold the 

string at an angle of 80" (figure IC) and again pull. Qualitatively, we note that the direction 

of rotation may change for a small change in the direction of pull on the string. 

:;:pl€j[@-F 

0x3 

tape joint 

movement 

pull 

(Cl 

pull 

rotat ion 

Equal and 

opposite force F 

I 

(d) (e) (f 1 

Figure 1. 

I 

I 

The explanation is in terms of a couple, which consists of two parallel forces, equal and 

opposite, which tend to rotate a body, as shown in figure Id. The product of one force with the 

distance between them is the torque of the couple. Figure 1 e shows what happens when the cord 

is parallel to the floor. The tension in the string and the reaction of the floor on the cup form a 

couple which acts to roll the cup toward the observer. When the string makes a large angle with 

the floor (figure lf), the couple rotates the cup in the opposite sense. Should the direction of the 

string pass through the line joining the points where the cups touch the floor, as in figure lg, 

there is no couple and the cups slide along the floor without rotating. 

Elastic forces, simple harmonic motion, gravitational and inertial mass 

It is amazing how much information you can derive from experiments using a ruler and a few 

marbles. Tape a Styrofoam cup to a ruler as shown in figure 2. Hold down the other end of the 

ruler, by its last five cm, very tightly to the books (used as a support). Now, attach a second 

ruler to the edge of the table as shown and notice the deflection of the end of the ruler as the 

number of marbles is increased. Qualitatively, the deflection is seen to increase with the mass in 

the cup. Does the ruler go back to its original position when the marbles are removed? Quantitatively, 

you can plot the extension against the number of marbles, giving a straight line, to show 

they are proportional to one another - an example of Hooke's law of elasticity. The deflection 

is produced by the weight of the marbles - the earth's gravitational attraction on them. 

Now, measure the time for ten oscillations for different numbers of marbles in the cup. YOU 

may have to push a crumpled sheet of paper in the cup to stop the marbles jumping around. 

I 311


Figure 2. 

Note the period (time for one oscillation), T, goes up as the number of marbles goes up - but 

they do not give a straight line if you plot one against the other. If you have no watch, remember 

a pendulum, such as a marble, on a string 99.4 cm long has a period of two seconds - each swing 

from side to side takes one second. Count the number of oscillations in ten seconds. If you plot 

the square of the period versus the number of marbles, however, you get a straight line plot such 

as figure 3. The appropriate formula is T = 27rfi where k is the spring constant, the force 

required to extend the spring by unif distance, and m is the inertial mass of the marbles. Let us 

suppose the spring extends a distance x when you put the marbles in the cup. The force is mg 

where g is the acceleration due to gravity (or gravitational field strength) and k = mg/x 

40 - 

30 - 

L 

(U 

D 

E 

2 

20 - 

1 0 - X 

I I I 

0 1 0 2 

T2/S2 

Figure 3. 

312


Since g is 10 m s-~ 

(or N/kg), you can check to see if T calculated from the static bending of the 

ruler agrees with the dynamic experiment. You can vary the spring constant k by shortening the 

part of the ruler which can bend. This experiment is quite important because simple harmonic 

motion is such a common phenomenon in physics. The gravitational mass of the marbles bends 

the ruler in the first part of the experiment, whereas it is the inertial mass we are using in the 

oscillation. Your experiment shows they are proportional. 

Velocity and acceleration 

A ruler with a channel down its length, a marble and some sticky tape, as shown in figure 4a, 

provide all the necessary materials to study velocity and acceleration. 

m 

Figure 4. 

Stick the tape across the groove in the ruler at zero, 7.5, 15 and 22.5 cm. Tilt the ruler so 

that, when released from the top, the marble just makes it to the bottom. Now set it going, 

and listen to the clicks as the marble drops off each piece of tape and strikes the ruler. The 

clicks are always equally spaced in time, however fast you set the marble going with your finger 

tip. What does this show? Are the times between clicks the same if one piece of sticky tape is 

removed? 

313


Since no horizontal forces act on the marble, it travels at constant velocity and covers equal 

distances in equal times. As the marble moves faster, the clicks come closer together, so a higher 

speed means the same distance in a shorter time, or a longer distance in the same time. Clearly, 

this provides a good intuitive feel for what we mean by velocity. Now tilt the ruler so that it 

makes a large angle to the table, and again release the marble from the top. Are the clicks still 

uniformly spaced in time? 

Stick the tape across the channel at 2,8, 18 and 32 cm. Tilt the ruler with two or three books 

as shown in figure 4b. Release the marble from rest at the top, so that it rolls rapidly to the 

bottom, making an audible click as it passes over each piece of tape, and at the end of the ruler. 

Are the clicks evenly spaced? Does it make any difference whether the ruler has a steep slope 

or not? 

Qualitatively, note that as the marble travels down the ruler, it is subject to a gravitational 

force, making it cover larger distances (between pieces of tape) ‘in the same time - so its speed 

(distance divided by time) is increasing - this is what we mean by acceleration under the action 

of a force. 

Quantitatively - the pieces of tape are distant from the top 1, 4, 9 and 16 units. These are 

12, 22, 32 and 42, so if the clicks are evenly spaced in time, the distance d travelled is propor- 

tional to the square of the time d = kt2. The steeper the slope, the larger the acceleration, but the 

clicks are still even, so d = k’ t2, with a new constant k’. 

240cm 

35 cm 

60cm 

15cm 

Ocm 

Figure 5. 

314

Dropping a string of marbles 


This technique for examining acceleration may be applied in a slightly different fashion. You 

require five marbles, a piece of string and some sticky tape. The string should be as high as the 

room, which we wil suppose to be 2.5 m. The marbles are taped to the string at intervals proportional 

to the squares of the whole numbers, i.e., 

Number 0 1 2 3 4 

Square 0 1 4 9 16 

Distance 0 15 cm 60 cm 135 cm 240 cm 

Difference 15 cm 45 cm 75 cm 105 cm 

Now stand on a chair, holding the string as shown in figure 5. The bottom marble should not 

quite touch the floor. Drop the string and listen to the clicks. They are more audible if you drop 

the string into a trash can, or onto a metal plate. 

You can repeat the experiment with a string having marbles spaced at uniform 50 cm intervals. 

Do you hear the time between clicks get shorter as the higher marbles from this last string strike 

the floor? Qualitatively, the higher marbles have been accelerated for a longer time, and are 

travelling faster, covering the same distance in a shorter time as they approach the floor than do 

the marbles starting near the floor. 

Quantitively, we have the familiar formula 

1 

distance = 3 g (time)2 

We spaced the marbles on the nonuniform string so the square roots of successive distances are 

proportional to whole numbers. The time taken between successive clicks should then be constant, 

about 0.175 s. Shift one of the marbles up or down the string to test the sensitivity of your ear 

to the time between clicks. A change of 20 per cent is easily detectable. 

The thermal expansion of a drinking straw 

This experiment on expansion requires three plastic drinking straws, sticky tape, very hot water, 

a pencil, a piece of card (or paper) and a cup. Bind two straws together very tightly along their 

hot water 

taDe 

hot straw 

bl 

Figure 6. 

315


length with sticky tape, as shown in figure 6a. Fasten the top end to a sheet of card or paper 

using tape. Mark the position of the bottom end very carefully. Now, you must use the cup to 

pour the hottest water available through the lower straw. To do so, make a little funnel by folding 

one end of the third straw, as shown in the figure, so that it wil fit into the top end of the 

lower straw. Slice the top end off the third straw diagonally to make it easier to pour through. 

Record how much the lower end of the straw shifts by making a pencil mark. Qualitatively, it is 

easy to see how the hot straw expands against the cold one, as shown in figure 6b, pushing both 

straws into a bow shape. 

It is also interesting to study the result quantitatively. Boiling water wil be at 100°C but if it 

is not available, measure the temperature using a thermometer. Measure the length of the straw 

L and the distance it moves, d. Then, the radius to which the straws bow, r, is given by 2rd = L2. 

If the centre of the straws is separated by a distance a, and the hot straw expands an amount 

x, then 

x=(r+a)0-r0 

where 0 = L/r 

x = aL/r = 2 ad/L 

The coefficient of linear expansion CY is given by the ratio 

Hence, 

CY = expansion/(original length X increase in temperature) 

= x/LT 

where Tis the temperature increase. 

d = -aL2 

1 

T/a 

2 

The coefficient is roughtly for the type of plastic of which straws are often made, so a 

temperature rise of 50°C where a is 0.5 cm and L is 20 cm moves the bottom end of the straw 

2 cm which is easily measurable. Heat loss and other problems generally gave rise to a low 

measured value for the coefficient. 

A drinking straw thermometer 

It is difficult for students to understand the concept of temperature without a thermometer. 

Here is a simple experiment requiring only sticky tape, a straw and a little water, which demonstrates 

Charles’ law as well as giving the temperature. 

Fold the end of a straw over two or three times as shown, and fasten it with sticky tape 

(figure 7). 

Fill the open end of the straw with about 5 cm of water (it may be easier to put the water in 

first, before sealing the other end). If you place the closed end in your mouth, you can see that 

the expanding hot air forces the water out. Remove the straw from the mouth, and notice how 

the air moves the water back up the tube (to its original position) as it cools. Now squirt cold 

water over the straw, or place it in a cold drink. The water wil move way back. 

316


Tape around 

2 or 3 times 

Straw 

Water in 

last 3 -5cm 

Figure 7. 

The thermometer may be used quantitatively by marking the position of the water meniscus 

(with a pen) on the side away from the open end, first at room temperature, then for the ice cold 

water, for your mouth, and for very hot (preferably boiling) water. You can calibrate your 

thermometer on the basis of Charles> law, which states that the volume of air, or length of the air 

column, is proportional to its absolute temperature (temperature in "C + 273). 

where Vi is the volume and L1 the length of the air column at temperature T1 OC, and V2 and L2 

the corresponding values at T,"C. Figure 8 shows typical measurements. The length of air at 

room temperature in this example Tr is 12.4 cm, for boiling water it is 16 cm, for ice water 1 1.5 

cm, and for body temperature TB it is 13.2 cm. 

Temp/K - 373 - 273 = 23.5 = - Tr = TB 

Length of air 16 11.5 12.4 13.2 

This gives room temperature as 29 1 K or 18"C, and body temperature as 3 10 K or 37°C. You can 

mark a linear scale (from 0 to 100) on the side of the thermometer if you can obtain the fixed 

points at 0°C and 100°C as described. 

d 16. Scm > 

5413.3 OScm 

Closed 

Ice water 

Room temp. 

Body temp. 

Boiling water 

Figure 8. 

317


It is difficult to place the whole length of the straw in the mouth or cup. Unfold a paper clip 

and drop it in the straw as shown in figure 9. The paper clip, within the straw, may then be bent 

to reduce the overall length. 

Figure 9. 

Longitudinal waves 

Longitudinal waves can be easily demonstrated with a weak spring such as a ‘slinky’, but rubber 

bands, marbles, paper clips and sticky tape can also be used. 

In order to observe their prokess, the waves must travel slowly, which means a spring of low 

restoring force and large inertia. 

Connect sixteen paper clips in a string using sixteen rubber bands, to provide the weak restoring 

force. A large inertia for the spring is obtained by attaching a couple of marbles to each paper 

clip with sticky tape, as shown in figure loa. Attach one end to a firm anchor - a desk or table. 

(The device works better if suspended vertically from the top of a doorway, for example.) Hold 

the other end taut with your left hand. Pull back the last marble with your right hand and release 

it (figure lob). Watch the compressive pulse travel along and be reflected. The wave is compressive 

because each marble moves in the same direction as that in which the wave travels, pushing 

the one ahead. Is the pulse compressive after reflection? If you have difficulty following the 

pulse down the string, watch the end marble closely - it jerks forward and backwards each time 

the pulse passes. 

A wave where the marbles move in a direction opposite to that in which the pulse travels is 

referred to as a rarefaction - so if you move the marble away from your left hand before releasing, 

you would generate a rarefaction. Sound waves are composed of successive compressions and 

rarefactions. The type of reflection you have been looking at occurs at a fixed end, i.e. the end 

of the string cannot move. In sound, such reflections occur in organ pipes closed at one end. The 

reflections from the two opposite ends of a pipe allow a standing wave to be built up in it. You 

can simulate such a standing wave by moving the hand holding the rubber band to and fro with 

different frequencies, until you hit a resonance. The marble near the far fixed end must be 

stationary. This is called a node. The end held by the hand is also a node, because of minimum 

motion there. The marble in the middle, in the lowest mode, (lowest frequency vibration) moves 

through a large amplitude, being at an antinode. Reflections from an open end (one not firmly 

attached to something) can be studied by fastening three or four rubber bands, without marbles 

or paper clips, between the far end of the device and the support (table or door, etc.). Feed in a 

comprehensive pulse. Is it reflected as a compression or a rarefaction? 

318


+ 

marbles 

tape 

Figure 10. 

Try producing standing waves. The end marble, which was stationary before, now moves more 

than all the rest - so the mode which was at the end has now become an antinode. 

If the device is hung vertically, and the lowest rubber band rapidly twisted by rolling it 

between the thumb and forefinger, the bottom clip and marbles spin rapidly, and pass this 

motion very slowly up the chain. At the top, the pulse reverses, and the marbles spin in the 

opposite sense. Reaching the bottom, which hangs free, the rotational pulse reflects as with an 

open end, the marbles continue to spin and wind up in the same sense, the pulse again travelling 

up the chain, and reversing at the top. This proves a quite dramatic demonstration of the difference 

in reflection between an open and closed end. 

Waves in pipes 

Having examined longitudinal waves, let us study their application in sound. 

The vibration of air in tubes is the mechanism whereby virtually all wind instruments sound. 

It also provides an excellent example of standing waves. All you need for these experiments are a 

few drinking straws, a sheet of paper and a pair of scissors. We shall study tubes open at both 

ends and those closed at one end; closed at both ends does not work because the sound cannot 

get out! The frequency of the note produced by blowing gently across the end of a drinking 

straw is that of the first normal mode of this tube. It takes a little practice to draw the note out 

of this instrument; you may have to vary the angle at which you blow and the distance from your 

lips in order to hear it, but with a little practice you should have no difficulty. The wavelength 

X of the first standing wave in an open pipe is twice the length of the pipe. Now, close one end 

of the straw while blowing across the other. The pitch falls an octave, since the first normal mode 

319


of a pipe closed at one end has a wavelength four times the length of the pipe. When the pitch 

falls an octave, the number of oscillations per second or the frequency, halves. In this mode, air 

rushes in and out of the open end, the motion diminishing towards the closed end, where it is 

zero, as shown in figure 11. Listen to the timbre of an open straw, and one which is half as long 

closed at one end. Although they have the same pitch, their sound is quite different. The open 

straw can vibrate with all the harmonics of the fundamental, but the closed straw possesses only 

the odd harmonics (i.e. three, five, seven times the frequency of the fundamental, etc.). 

Amplitude of 

vi brations 

t 

Figure 11. 

One can make a pitch pipe from a straw, since its frequency depends only on its length, and 

the velocity of sound, which is 344 m s-l at sea level and room temperature. The top string of a 

guitar is tuned to E4 (329.6 Hz) which would be given by an open ended straw 52.5 cm long. It 

is more convenient to use a straw 12.5 cm long, which, with one end closed, gives the octave of 

this note. A correction should be made for the finite width of the straw. One should add 0.82 of 

the radius for each open end, so this amount should be subtracted from the length of the straw 

given above. 

Vibrations in pipes open at both ends are represented musically by such instruments as the 

flute family, and the open flute pipe in an organ, often called the open diapason. However, most 

wind instruments employ reeds to provide vibrations, and these act effectively to close the end 

of the pipe. We can make simple reed devices with paper and straws with which to experiment. 

Take a 15-20 cm square of paper and fold along one diagonal, Then open it out and proceed 

to roll the paper tightly around a pencil from one end of the diagonal crease to the other end, so 

that the diagonal rolls along itself as shown in figure 12. If a six-sided pencil is used, do not wrap 

it too tightly, or the pencil wil not come out. When completely rolled, it should resemble the 

lower figure. Push the pencil out and glue the last fold at A, or hold it in place with a rubber 

band or strip of sticky tape. 

Now from the point marked b in figure 13, at one end cut away on each side, in the direction 

indicated by the small arrows, until the end piece may be opened out into a triangular shape c. 

The cuts must be at right angles to the main roll and are each a trifle over one-third of the 

circumference of the rolled tube. Fold the triangular piece at right angles to the tube SO that it 

forms a little cover over the end. Now place the other end of the tube in your mouth, and instead 

of blowing, draw in your breath. This action wil cause the little triangular paper lid to vibrate 

and the instrument wil give a bleating sound. The noise can be made louder by poking the tube 

320


A 

I 

Figure 12. 

Figure 13. 

through a hole in the bottom of a Styrofoam cup, as shown in the figure, or through a paper cone 

which you can roll. This type of reed, in which the flap closes off the aperture completely, is 

known as a 'beating reed', and is used in the clarinet, oboe and bassoon. The clarinet has one 

reed, and the oboe and bassoon two reeds beating together. 

One can make another type of beating reed from a drinking straw. Fold over the end of the 

straw, as shown in figure 14a, and tape it closed. Take a razor blade, or sharp knife, and make 

a rectangular cut about 2 to 3 mm wide, and 2 cm long. Put the whole of the reed in the mouth 

and blow, as shown in the figure. It can generally be made to sound by very slightly lifting the 

reed, and bending it up, so that when at rest the hole in the side is a little open. Such a reed is 

very similar to that used in the drone of a bagpipe, or such antique instruments as the hornpipe. 

32 1


Figure 14. 

So far, we have provided examples of single reeds, but a double reed can be made from a plastic 

soda straw by cutting slits on either side at the end, as shown in figure 14b. Some practice is 

required in blowing this device. It is said that chewing the cut end between one’s molars so that it 

is flat greatly improves the response. Press the reed between the lips while blowing - the range of 

pressure under which you can make the reed sound is restricted, and you need to blow rather 

hard. This is similar to the double reed in an oboe. As before, you can insert it into a paper cone 

or Styrofoam cup, to demonstrate how the cone matches the impedance of the instrument to the 

air, and hence greatly increases the volume of sound. Now try cutting the tube of the reed pipes 

shorter and shorter. Note how the pitch of the reed goes up and at some point the reed stops 

functioning. Clearly, the air in the tube is necessary to the functioning of the reed, even though 

the length does not determine the pitch in the same way as it does for an open pipe. After 

cutting the pipe shorter, roll a tube of paper around the outside and tape it as shown in figure 

1 Sa. Slide the outer tube up and down. The pitch goes up and down as you slide the tube in and 

out and you can measure the frequency as a function of the length. Listen to the timbre of the 

note produced. It is almost a quacking or bleating kind of tone. This is because a puff of air is 

allowed into the pipe each time the flap opens and closes, and such sharp puffs have a lot of high 

frequencies in them, in addition to the lowest frequency, or fundamental. Now, cut the corners 

off the paper reed, as shown in figure 15b. (Take care that the reed covers the tube - otherwise 

it wil not work.) Observe that the pitch goes up. The natural frequency of vibration of the reed 

is higher, the smaller the mass oscillating. 

Figure 15. 

322


In an orchestral wind instrument the reed is not free to vibrate at its natural frequency, but is 

forced to oscillate at the resonant frequency of the tube of the instrument. The paper reed can 

only vibrate at a low frequency, so you would need a tube about a metre long to be able to bring 

this reed into resonance with the fundamental mode. If you have such a tube you could try it out. 

We can examine the way the voice works using this device. The paper or styrofoam cup, which 

we placed over the end of the tube, has its own resonant frequency. The vocal tract (larynx, 

mouth) behaves similarly in the case of the voice. The resonance is at a high frequency and tends 

to emphasize frequencies produced by the reed or vocal cords in this vicinity - these resonant 

frequencies are called formants in the case of the voice, and determine whether you are saying 

‘00’ or ‘ah’, even if your voice holds the same basic fundamental pitch. 

While sucking on the reed, close the cup partially with one hand, then open it again. Doing 

so alters the formants, and it is quite easy to get the device to say ‘ma ma’ or even more difficult 

vowel sounds with a little practice. (This is similar to the ‘wa wa’ sound obtained by opening and 

closing the mute on a trumpet.) 

Transverse waves 

It is difficult for students to get an intuitive feeling for wave motion. The next experiment is a 

simple modification of a well-known wave machine. It also makes an excellent mobile to hang 

in the classroom. You wil need only 1 m sticky tape, about two dozen drinking straws, and 

twice as many paper clips. Unwind about 70 cm of the tape. Fold over one end and stick it to the 

table. Run the tape along the table, and fold over and stick the other end down, as shown in 

figure 16a. Place one paper clip in each end of every drinking straw, as shown in the figure, and 

stick the centre of the straws at 2.5 cm intervals along the tape, until all twenty four are attached. 

Then stick the device to the edge of the table, as shown in the lower part of the figure. 

Figure 16a. 

323


Figure 16b. 

Now, look at the straws end on, pull the end of the tape downward to make the tape taut, and 

give the bottom straw a tap. You wil see a transverse wave pulse travel up, and be reflected at the 

top. Since the top is fixed to the table, the sign of the pulse is reversed as at a fixed end (figure 

17). If there is a long length of tape at the bottom, a downward travelling wave pulse is reflected 

as at a free end, without change of sign (figure 18). You may produce standing waves by rotating 

the bottom straw to and fro with the right period. 

For the last twenty c m or so of the tape, put two paper clips in each end of the straw. NOW 

you can study the reflection and transmission of a wave travelling from a less dense to a more 

dense medium (top to bottom) or vice versa (bottom to top). Note how in each case, part of the 

wave is reflected at the interface, but whereas for a wave going from a less dense to a denser 

medium, the reflected pulse is inverted (phase reversed), in the other case, it is not. 

r== 

Table 

Reflected 

Pulse 

Figure 17. 

324


Pulse- 

Held under 

tension- 

0 

CD 

a 

c= =a 

e P 

Table 

t 

L 

t 

~= Pulse reflected 

same sign from 

:= a free end 

Figure 1 8. 

Optics - positive and negative lenses 

This experiment requires clear sticky tape and a drinking straw to make a lens with water. Stick a 

piece of clear transparent tape flat over the end of a straw and cut a piece 1 cm long from that 

end. Place the tape over some object - a fly, or a printed letter - and fill the piece of straw, 

using the longer piece sucked full of water (figure 19). 

Make sure the meniscus stands high on the straw. Now, look down through the straw. You wil 

see a magnified image of the object underneath. As the water leaks out of the bottom (or, you 

can soak up a little with toilet paper) the meniscus changes shape. When it stands high, we say it 

close off end 

with finger 

press to produce 

drops 

cct Piece of straw 

- r w 

'2% 

tape 

A 

I 

I 

K 

I 

I 

wa'ter meniscus 

stands high 

object 

Figure 19. 

325


is convex. Hence, a convex lens can magnify in the same way as a magnifying glass, producing an 

image larger than the object. As the water leaks out, the surface caves in, and we say it is concave. 

Look at the object through the water now, and you see it appears much reduced in size, as it 

would on looking through the wrong end of a pair of binoculars. Concave lenses therefore give an 

image reduced in size. What do we learn? 

Qualitative: Convex lenses (bowed out) magnify; concave lenses (bowed in) give images 

reduced in size. 

p 

\ I 

\ I 

Quantitative: The ray trace of the system is shown in figure 20. Look at the little square 

(figure 2 1 a) through the water lens. When the meniscus is convex, it looks like figure 2 1 b. This 

is known as barrel distortion, because the square image is distorted to look like a barrel. Distortion 

of this kind occurs with all lenses having spherical surfaces, such as this. When the lens 

becomes concave, the distortion changes and becomes pincushion distortion (figure 2 IC). 

radius of 

surface 

no magnification 

\ I 

\ I 

\ I 

\ I 

\ I 

A 

large virtual image 

n- the refractive index. 

the ratio of the speed 

of light in air to that 

in the medium. 

flat surface 

\ / 

+ I 

I H 

I 

H/n 

Figure 20. 

-image of 

reduced size 

o 

tal 

Figure 21. 

326


We can employ our little water lens to give a real image. Fill the lens until the surface is convex 

(bulges out). Now, hold the lens vertically under the room light, a few inches above a sheet of 

paper. Move the lens up and down until you get an image or picture of the light on the sheet of 

paper. Because it actually lies on the paper, this is called a real image. The image is distinct, but 

not very clear. Notice as water leaks out (or if you soak up a little on toilet paper), the image 

gets farther away from the lens. We say the focal length (the distance from the lens where a point 

very far away focuses) is increasing. Notice also that, as this occurs, the image gets bigger (figure 

22). 

-\ Image 

Figure 22. 

We learn from this that a convex lens can form a real image, as shown. In the case of our water 

lens, the bottom surface is flat and we can calculate the radius of the top surface from the lensmaker's 

formula for this lens, found in most optics texts. 

where n = refractive index of water = 1.33 

U = distance of object from lens 

v = distance of image from lens 

Y = radius of curvature of the water surface 

327


The pinhole camera 

It is a problem to devise optics experiments which don’t involve lenses. This one requires two 

paper cups, tape, thin paper and aluminium foil (or dark cloth) to black out light. Punch a hole 

with a pencil in the bottom of one cup and 

v 

cut a hole about 2.5 cm in diameter in the bottom 

of the other as the eyehole. Tape a sheet of paper over one cup, and attach the other, as shown 

(figure 23). 

thin sheet of paper 

/ 

PINHOLE VIEWER 

Figure 23. 

328


Now, cover the whole of the two cups, apart from the eyehole, with one sheet of aluminium 

foil. The pinhole is made with a paper clip in the foil over the front cup. If aluminium foil is not 

available, make the pinhole in the front cup, then render the two cups opaque with black ink, or 

a dark cloth. Holding the cups up, an image is projected on the paper by the pinhole, and may be 

observed through the peep hole. Widen the pin hole. What happens to the definition (sharpness) 

of the image? Is the image brighter? The image of an incandescent lamp, the sun, or other light is 

easiest to observe. What is the relationship of the size of the image to the size of the object? Is 

the image erect or inverted? 

Experiments with magnets 

Experiments with magnets give students a lot of physical insight, with very little equipment, since 

about the only primary prerequisite is a magnet! These may be purchased in the store, but if you 

are going to buy them in bulk, it is probably better to get several of the chubby alnico bar type. 

An obvious experiment is to use the magnet as a compass, which can easily be done by hanging 

it by a thread, or floating it on a piece of Styrofoam on water in a Styrofoam cup. 

We can check the attraction of unlike poles by magnetizing a paper clip and using it as a 

compass. Take the clip, and, holding it as shown in figure 24a, stroke it from end to end with one 

pole of the magnet a large number of times, always in the same direction, Hang the clip from a 

thread, as shown (figure 24b) so that it balances horizontally and see in which direction it points. 

The thread should be as long as is convenient so that the twist of its fibres supplies a minimum 

torque. Notice that the end of the clip where the stroke finishes has opposite polarity to the pole 

b 

a 

- 

d 

Figure 24. 

3 29


doing the stroking. Bring up the north pole of the magnet, and see that it repels the like pole of 

the clip and attracts the opposite end. The stroking magnetizes the clip because the strong 

magnetic field causes the magnetic domains of which the clip is composed to align with the field. 

We can plot the lines of force around our magnet using the paper clip hung on the thread. 

The clip orients itself along such lines, the poles at opposite ends being forced in opposite directions 

to provide the torque. Hold the thread supporting the paper clip as far up as possible to 

minimize the thread’s restoring torque. A small piece of tape on the clip airdamps vibrations. 

Tape the magnet to the centre of a sheet of paper, support the clip somewhere near the magnet, 

and lower it gently to the paper. Draw a pencil mark along the line where the clip touches the 

paper as shown in figure 24c. This is a field line. Now, move the clip a little farther along, and try 

to make a continuous field line. Do this all around the magnet, (figure 24d) holding the thread 

closer to the clip as you approach the magnet, to prevent it being drawn in. For a very small 

magnet, the lines of force follow curves of the form drawn in figure 25. Compare them with the 

lines you obtained. A larger magnet tends to make the loop flatter 

\ 

Figure 25. 

330


So far, the experiments have been somewhat qualitative. However, we can construct a tangent 

magnetometer which wil measure the strength of our bar magnet by comparison with the earth's 

field. 

The magnetized paper clip is hung by a long thread from a table or chair, as shown in figure 26, 

to swing just above the floor. Make sure the thread is unwound so that it provides the minimum 

torque, and that the piece of tape attached to the clip acts as an air damper. Place the graduated 

circle of figure 26 beneath the clip so that 0" is orientated north. 

W 

S 

Figure 26. 

Bring up the magnet with its axis along the 90" or E. W. line, as shown. Two couples act on the 

clip. One arises from the horizontal component of the earth's magnetic field He, and the other 

the field at the clip produced by the magnet H,. When the paper clip is sitting at an angle 8 to 

the north, as shown, the two couples are in equilibrium: that due to the earth's field is mH,L sin 0, 

where m is the pole strength of the paper clip, and L the separation of the poles. The magnetic 

moment, M is equal to mL, and the couple due to the magnet is 

H, M cos e 

33 1


Then 

or 

H,M sin 8 = H, M cos 8 

tan 8 = H,/He 

The horizontal component of the earth's magnetic field varies with geomagnetic latitude. It is 

approximately 0.2 gauss on average (in air, 1 gauss = tesla), but a map for this component 

is given in figure 27. There is also a slow secular variation of this field. Using these values, it is 

possible to calculate the field strength produced by the bar magnet a distance d from its centre. 

The edge of the circle has been graduated in units of 0.2 tan 8, so that you can read the values, 

of a field H, directly off the circle, for a place where the earth's field is 0.2 gauss. 

- 

120' 150. 180° 150' 120. SOo 60° 30° Oo 30° 60' SOo 120° 

Figure 27. Map showing lines of equal geomagnetic horizontal intensity H (in lo-' 

Office.) 

tesla) for 1975. (US. NavaZOceunographic 

Far along the axis of the bar magnet, the field is given by M/r3, where Y is the distance from 

the centre of the magnet to the paper clip. It is simple to check on this relationship, by plotting 

the measured field strength against l/r3. The most accurate readings of H, are obtained when 

8 is approximately 45", so it is a good idea to start by placing the magnet at a distance giving 

this deflection. With the magnet placed at position B, rather than A, the field at the clip is again 

perpendicular to that of the earth, and is given by 2A4/r3, which can also be checked. This experiment 

makes the point that we can get a reasonable quantitative value for the magnetic moment 

of a magnet using the earth's field for calibration. Most experiments do the inverse to use a 

calibrated magnet to obtain an accurate value for the earth's field. 

332


Current electricity 

We have so far dealt with experiments on mechanics, heat, light and similar topics, but string and 

sticky tape does not lend itself so easily to experiments on electricity. The addition of a roll of 

aluminium foil to the other simple materials allows one to perform a number of experiments on 

static electricity, but the problem of current electricity can only be solved by a source of direct 

current (d-c.). Batteries are most often used in schools, the large 1.5 V cell being common. However, 

such large cells are expensive, especially if you use one per student. Furthermore, I believe 

there is a law, closely related to Murphy’s law, which states that whenever a battery is required 

for physical experiments, it is always flat. The reason is, of course, that such batteries are 

commonly employed only once or twice a year, and their shelf life is of this order. Furthermore, 

students often short circuit the batteries unintentionally for considerable periods of time. I 

contend that the best source of d.c., and also low voltage alternating current (a.c.1, is a model 

electric train supply. The HO-gauge power supply provides d.c., variable from 0-15V, and is 

cheap. Suppliers give reductions for bulk orders, but I have discovered that many high school 

students are willing to bring in their personal supplies, having passed through the model train 

stage of their development. 

The only difficulty with such power supplies is that often they do not give as large an instantaneous 

current as a battery (although supplies up to 2.5A are available), but they can be short 

circuited more or less indefinitely, and are virtually indestructable, having been designed for the 

use by small children. Most important, they never go flat. 

1.5 

1.3 

> 

\ 

a, 

a 

Q 

m 

1 .I 

- 

0 > 

- 

a, 

U 

U 

J 0.9 

U 

I 

U 

U a, 

[I] 

- 

U 

0 0 -7 

I I I I 1 I I 

0 200 400 600 800 1000 1200 

Time / minutes 

Figure 28. 

333


A word or two about batteries is in order. The amount of energy stored in a battery of a given 

design is roughly proportional to its volume. The maximum current which can be drawn is 

proportional to the area of the electrodes. The most commonly used cell, the LeclanchB or Zn:C 

cell, relies on the potential between zinc and carbon electrodes with a moiste paste of ammonium 

chloride as the electrolyte. The D-type cell is the one bought most often. Manufacturers rarely 

give the shelf life of such cells, which vary from less than a year to two years. Figure 28 gives the 

discharge characteristics of such a cell, as compared with a typical alkaline cell. The decision must 

be made whether to buy such a cell, or one of the newer alkaline cells. Neither one is rechargeable. 

The alkaline manganese dioxide primary batteries (which have a potassium hydroxide electrolyte) 

retain 80 per cent of their ampere-hour capacity after four years, so that they are preferable, 

even if they cost twice as much as the Zn:C cell. Furthermore, they can give between four and 

six times as much energy as the latter. The actual energy delivered depends to a great extent how 

a battery is used. Some are meant to deliver large currents for short periods (as for electronic 

flashes), others small currents for long periods (watch batteries). 

Now for a simple experiment to show that currents in the same direction attract, and in the 

opposite direction repel. Cut a strip about 1 cm wide and 70 cm long from a roll of thin household 

aluminium foil.Fold it in the middle, and tape the two ends to the edge of a table, as shown 

in figure 29, then run the fingers down the two adjacent parts of the strip to bring them as close 

together as possible without touching. Cut two more pieces of foil to connect the ends attached 

to the table to the opposite sides of a battery or power supply. As the connection is made, the 

two parts of the strip wil repel and move apart slightly, since they carry current in opposite 

directions. 

tape 

Figure 29. 

334


For a large audience, the strip can be folded and laid loosely across an overhead projector, 

taping the ends of the strip to the edge of the projection plate. The motion is not as large, because 

of friction with the transparent plate, but the magnification makes it easily visible. To show that 

currents in the same direction attract, the top ends of the folded strip are taped together and 

attached to one terminal of the supply, and the fold at the bottom end attached by a separate 

foil strip to the other terminal of the supply. This time, the two parts of the strip wil move 

together as shown. It is possible to use either a d.c. or a.c. supply in this experiment, but connecting 

directly across the mains supply is definitely not recommended - you wil either blow a fuse 

or melt the aluminium! 

A current balance 

Many more experiments are possible if a coil of wire is available. The kind called ‘Magnet wire’ 

(number 22 gauge insulated is good) is probably the best to buy. Here is a simple experiment 

designed by E. J. Wenham for the British Nuffield Physics course [2]. It requires a small alnico 

magnet (about 1.2 cm long and 0.4 cm square) a drinking straw, a needle and a small channel 

made of card such as the outside of a match box, to support the needle. 

Fasten the magnet near to the end of the drinking straw with about 4 cm of sticky tape (cut 

to half width) (see figure 30). Balance the straw across your finger to find its centre of gravity, 

and stick the needle through the straw about 1 mm farther away from the magnet. Wind a coil 

of wire about 25 mm diameter with about 20 turns and fix it with sticky tape to the table top 

close to the end of the channel, which is made by cutting the match box top so that it stands 

about 5 mm higher than the top of the coil (figure 3 1). 

magnet 03 

Figure 30. Making the magnet assembly for a current balance [2]. 

335


/ 

/ 

Figure 31. The assembled current balance [ 31. 

Rest the drinking straw on the channel, with the magnet on the axis of the coil. 

Now cut about 2 cm of wire and bend it into a U to act as a counterbalancing rider on the 

straw. Use sticky tape to hold a second straw vertical just by the end of the balanced straw - 

and mark the position of the balance on it. If correctly connected into a series circuit with say, 

two 1.5 V cells and two 1.5 V lamps, the magnet wil be pulled into the coil. When balance has 

been restored by sliding the rider along the straw, the current balance can be used to check 

whether or not the current is the same at all points in the circuit by connecting it between the 

lamp, between the cells, and between the cells and the lamps. This demonstration is very important 

in understanding current electricity. If a commercial ammeter is available the balance can be 

calibrated with a set of current markings made along the straw. 

TEACHING PHYSICS USING NEW GAMES 

There has been a move afoot among child psychologists for quite some time to change certain 

of our attitudes towards games. In the past, games have been primarily competitive, the object 

being to beat the opponents. Any co-operative spirit arose through one team combining against 

336


the other. Not all children are so combatively inclined, however. As a result, games have been 

devised which allow for a spirit of co-operation without the concomitant aggression. One such 

is the lap game [3, p. 1721 . In this, the group forms a circle, and each individual sits on the lap 

of the individual behind. The world record used to be 1500 lap-sitters. Of course, if one person 

falls over, a co-operative effect - essentially a soliton wave of non-lap-sitters - moves around the 

circle. The speed with which this occurs, though not equal to the speed of sound, is nevertheless 

very rapid. Many such games can be devised to demonstrate physical principles. In a large class, 

interaction on a personal basis, not merely between the teacher and the student, but also between 

the students themselves, is virtually nonexistent. Furthermore, such large classes are given, more 

often than not, in vast auditoria not designed for physics use, where there are no apparatus 

storage facilities, and it is difficult for the students at the back to see. The difficulties of interesting 

the students in the course can be greatly facilitated by involving them directly in demonstrations. 

For example, the students can be invited down to the podium to demonstrate gas 

kinetic theory. A few of them mill around, bumping into one another, pretending they are ‘gas 

atoms’. This contact sport is evidently much appreciated by the students, provided it is not 

carried too far. More students come down, making closer contact, hands on shoulders, but breaking 

away to put hands on the shoulders of different students to form a liquid. Then, they put 

hands on the shoulders of the nearest individual and stick - a solid. Such simulations: 

1. wake up the students 

2. act as demonstration experiments 

3. require no setting-up time or equipment 

Acting out really drives home the point. 

I hear and I forget. I see and I remember. I do and I understand. (Chinese proverb) 

Of course, the question arises as to how much is physics and how much game, but such experiments 

seem an excellent idea in moderation. Which type of physics lends itself to such methods? 

People are particles, so clearly gas kinetic theory is suitable - and in fact, many quantum 

phenomena can also be described (short of tunnelling through a potential wall). Here are some of 

the ideas we have tried out, together with the principles which they aim to demonstrate. 

Pirates treasure game (vectors) 

It is notorious that pirates always bury their treasure beneath some beach on a desert island, and 

then provide a nearly incomprehensible map to find it. The object of this game is to provide a 

suitable vector description for finding the treasure, using paces as the unit of length. It should be 

remembered that the pace was the unit employed by the Romans, whose professional pacers’ sole 

job was walking between towns to measure the distance. So we can start by saying ‘take three 

paces north (or towards the blackboard, or whatever) and four paces west. Count the paces 

directly back to where you started (which would be five) and continue beyond by the same 

number’ --until you arrive at the desk with the treasure in it. The aim is to combine distances 

vectorially and reach the point where you wish to go. 

The three-metre dash (kinematics) 

To emphasize the difference between velocity and acceleration, we have two races - one a dash 

of three metres, and the other a more normal length up to 50 metres, or whatever is available. 

The students who accelerate most rapidly are not necessarily the ones who can do well over 

distance. Stamina plays no part here - it is inertia which counts. 

337


The knee-bend game (energy and power) 

The participants do a knee bend, and the distance from some suitable part of their anatomy to 

the floor is measured. They then stand up, and the same measurement is made from this position. 

Most people know their weight, so the work done, mgh, mass times the acceleration due to 

gravity times vertical distance risen, is easily calculated. For example, if your mass rn is 50 kg and 

the distance h risen on standing is 60 cm, the work is 50 X 10 X 0.6 = 300 joules. The work 

performed on rising is not regained on sitting - unlike a bicycle running downhill, we do not 

store the potential energy on doing a knee bend - it is lost as heat. Some student is bound to 

have a watch with a second hand, so the next portion of the game is to see how quickly you can 

do ten, twenty, fifty knee bends. The power is then the rate of doing work. If you do 40 per 

minute, in the above example, the power would be 300 X 40/60 = 200 watts. Generally, the rate 

of doing knee bends is about the same for men or women, but women weighing less, their power 

is also correspondingly less. One can also perform a similar game running up and down stairs and 

measuring the power required - however, one should avoid giving older students heart attacks. 

The wave game 

This one is great fun. Students stand in a line, fairly close to one another, and put their hands on 

the shoulders of the individual in front. The one in front of the line rests his hands against a convenient 

wall.The last in the line gives a hearty push to the one in front, who (to avoid falling) 

pushes the one in front, and so on. This resembles the game played with a line of dominoes 

placed on end. When the front is reached, a push is given against the wall,and the compressive 

longitudinal wave travels toward the back. About the only problem in this game is attenuation of 

the waves - a really good push is needed to avoid this. To simulate reflection at an open end, the 

last person in the line pulls the shoulders of the individual in front, who pulls the shoulders of the 

next in front, and so on. The front of the line, on being pulled back, and having no one to tug 

on, falls back and ‘reflects’ the rarefaction as a compression. This is not as self-generating as the 

compressive wave. The wave wil rapidly attenuate unless positive feedback is inserted - each 

student, on being pulled back, must make a conscious effort to pull back the student ahead. I 

have found, when the students see what is going on, that it makes understanding a difficult 

concept much easier - and enjoyable! 

Transverse waves can be simulated by the last student pushing the one ahead sideways. Again, 

this travels to the front, where, if the student has nothing to hang on to, a reflection of the same 

sign occurs. If the student hangs on to a doorway, or other solid object, the pulse is reflected 

with change of sign. Another way to propagate transverse waves is for the students to hold hands 

in a line, facing perpendicular to the line, and for the student at one end to start a wave which 

wil travel to the other end. If the student at the far end is holding on to something, again the 

wave will invert, but if not, it wil reflect with the same sign (or the student wil fall over). A 

variation of this game is seen in ‘crack the whip’ played by a line of ice skaters. 

Further suggestions for games may be found in the New Games Book [3], for example, for 

statics, the pyramid game [3, p. 571, and the stand-up game [3, p. 651 are good. Interesting 

suggestions for the way fundamental physical concepts apply in games wil be found in Peter 

Werner’s book, Learning through Movement [ 41 . 

Having found this concept works, you may be inclined to design your own games. One such 

game in the middle of a long 70 minute class both wakens and relaxes the students! 

338


CONCLUSION 

In conclusion, the principal hindrance in utilizing the experiments discussed above is procrastination 

or inertia. The difficulty of getting the items of equipment together on the part of a busy 

teacher is always a problem. I can only say, on the basis of my own experience, that once the 

gear has been collected, the students really appreciate being able to perform experiments themselves. 

The satisfaction in seeing how physics operates outweighs the outlay in time and effort - 

and the equipment wil also be ready for next year’s class. 

REFERENCES 

1. 

2. 

3. 

4. 

The Physics Teacher. Stony Brook, N.Y., American Association of Physics Teachers. 

NUFFIELD FOUNDATION SCIENCE TEACHING PROJECT. Revised Nuffield Physics. Years I and 2. Teachers ’ 

Guide. Revised ed. London, Longman, 1978. 

NEW GAMES FOUNDATION. New Games Book. Garden City, N.Y., Doubleday, 1976. 

WERNER, P.H.; BURTON, E.C. Learning through Movement: Teaching Cognitive Content through Physical 

Activities. St. Louis, MO., Mosby, 1979. 

ACKNOWLEDGEMENT 

With the exception of figures 27, 30 and 31, the illustrations are redrawn from EDGE, RD. String and Sticky 

Tape Experiments. Department of Physics, University of Carolina, United States. 1980. 

339

Part VI 

Science, Technology and Society

Introduction 

Although school curricula are overloaded with subjects, and subjects with material content, there 

is a growing realization that science teachers in general and physics teachers in particular cannot 

continue to ignore the relationship between their science and the society in which they are 

working. 

The first two papers in this section outline two of the earliest successful attempts to formalize 

this important trend. The major problem for those who may wish to emulate these pioneer 

programmes is the discovery of a niche within the school programme into which the work may 

be fitted. In these two cases, that problem was solved very ingeniously and, although the courses 

can directly affect relatively few students, the effect of teaching them certainly changes the 

teacher’s approach to the rest of his teaching. These courses are proving to be powerful catalysts 

for change. 

One hears so much about alternatives to high technology and much that is of a somewhat 

vague nature, that we asked an engineer working in the field to write a paper which would be 

both realistic and practical and which would provide suitable background material for a teacher 

who wished to know more. This then is the theme of the third paper in this section. 

343


The teaching of science in relation to society 

J.L. LEWIS. 

Changes in physics teaching in the last twenty-five years have been profound. Before the era 

heralded by the Physical Science Study Committee (PSSC) in the United States, there was a great 

emphasis on the acquisition of factual knowledge. This was reflected in examination questions 

which depended almost exclusively on recall: the recollection of formulae and precise definitions 

as well as the description of routine experiments. First the PSSC course in the United States, 

followed by the Nuffield projects in the United Kingdom, and then by a series of new projects 

throughout the world, began to put more emphasis on the process of science; physics was no 

longer seen as a number of isolated topics, but as a fabric of knowledge. There came an awareness 

of the importance of students doing experiments in which they looked for evidence; there 

was a conscious attempt to let students feel what it was like to be a ‘scientist-for-the-day’. The 

student became actively involved in the process of learning instead of passively receiving the 

teacher’s flow of information. Physics education seemed to be more fun than it had been. Was 

all well? 

THE IMAGE OF SCIENCE 

There was increasing evidence that the image of science amongst young people was a regrettable 

one. In their idealism, they were turning away from science as though it were associated with 

most of the evils in the world. For them, physics was the bomb, chemistry was pollution, biology 

was genetic engineering (assumed to be evil) and industry was dirt, boredom, grease and yet more 

pollution. They tended to link science and warfare together. Some of the blame for this unhappy 

image must inevitably rest with those of us who taught them their science. 

There must be some significance in the fact that so many students seek university courses 

associated with people; the pressure on places in medical schools is always high, but it is also high 

for courses in law, social sciences and the humanities. No doubt there are economic factors 

involved, but perhaps it is unfortunate that in our teaching we have done little to show that 

science has much to contribute to people and to the well-being of society. 

Professor Paoloni in Italy has pointed out that in his country the word ‘chemical’has come to 

be synonymous with ‘harmful, noxious, dangerous’. And this is probably the same in many other 

countries. Even the image of the scientist - in white coat, standing at a bench and peering at an 

344

Science in society 

array of bubbling flasks and glass tubes or surrounded by switches, wires and meters, gazing 

intently at an oscilloscope - is not a flattering one. It does not suggest that science has much to 

do with people or the welfare of society. 

Perhaps we have enjoyed ourselves a little too much in the last twenty-five years playing with 

ticker-tape, trolleys and our electromagnetic kits, or looking for evidence for the existence of 

energy levels. Those things are still extremely important, but perhaps we should have spent a 

little of our time showing that the physics we enjoy is very much concerned with society, and 

that it has a contribution to make. 

RELEVANCE TO THE NEEDS OF SOCIETY 

Professor Paul Vitta from the University of Dar es Salaam in the United Republic of Tanzania 

was a member of Science and Technology Unit of the Economic Commission for Africa preparing 

for the United Nations Conference on Science and Technology for Development (UNCSTD). 

He listed the developments in Africa most in need of science and technology: 

Agriculture 

Health 

Animal breeding 

Water 

Mines 

Industry 

Communication 

Transport 

Energy 

Environment 

Construction 

Posts and Telecommunications 

Such a list does not apply only to Africa. These are issues with which we are all concerned, but 

to what extent are they reflected in our science teaching? Physics, for example, has a contribution 

to make to each of them, but how often do we allow our students to appreciate that? 

The relevance of physics is obvious to the post-graduate because it is at this stage that he earns 

his living by putting his physics to use. Some of the responsibility for the apparent lack of 

relevance must lie with the pyramid structure of education: work at primary stage is too often 

seen merely as a foundation for the secondary stage, which in turn is the foundation for university 

courses. Seldom is education at each level seen as an end in itself, even though only a fraction of 

the pupils at each level progresses to the next stage. Inevitably and understandably, universities 

prefer secondary schools to provide a sound knowledge of basic physics on which they can build, 

and their influence on secondary schools can be considerable. But ought physics courses at the 

secondary level to be more self-contained and balanced since only a small proportion of those 

studying physics at school wil ever study physics at a university? 

To illustrate this, let us consider how energy was taught in schools in the past. Energy has been 

part of science education as long as physics has been taught in schools, but not as the exclusive 

preserve of the physicist since the chemist and the biologist inevitabIy incorporated the concept 

into their teaching. However, it was the physicist who attempted to give it precise definition, 

usually relating it to work as force F times distance s. This in turn led to a mathematical treatment 

and a series of formulae which filled students’ notebooks. 

1 

s = ut 4- --at2 

F=ma 

2 

u2 = u2 + 2us 

Fs=-mu2 1 --mu2 1 

2 2 

Work = Fs 

1 

- mu2 

2 

345


Of course this was good training for those of us who went on to universities, but it gave very little 

feel for the concept of energy. Few would now deny that students ought to consider the sources 

of energy and the uses to which it is put in our homes, in the community and in society. Some 

understanding of how electricity is generated and distributed should supplement school experiments 

on electric currents. Of course, a detailed treatment of nuclear physics may not be 

appropriate in schools, but some understanding of energy seems essential to young people 

emerging into a world in which decisions have to be made about nuclear energy. Otherwise 

nothing but emotion wil govern their decisions. 

For many of us in our undergraduate days the teaching of entropy was enshrouded in a series 

of thermodynamic equations very remote from reality. We acquired great skill in manipulating 

those equations, especially since such manipulation gave satisfaction to the examiners, but how 

much understanding did we really have? Yet the second law of thermodynamics is fundamental 

to the use of energy in society today. Our teaching should bring out that relevance. 

ONE ATTEMPT TO FIND A SOLUTION 

Over ten years ago the Association for Science Education (ASE) in the United Kingdom was 

advocating that in addition to Pure Science (Science for the Inquiring Mind), there should be two 

other components in Science Education: first, ‘Science for Action’ and secondly, ‘Science for 

Citizens.’ We learnt about conduction, convection and radiation in our study of pure science, but 

where to put a convector heater in a room was ‘Science for Action.’ It was less obvious how we 

could incorporate the component ‘Science for Citizens’ into our teaching. Five years later James 

Callaghan, then Prime Minister, speaking at Ruskin College, urged that science teaching should be 

more relevant to the needs of society. Science teachers did not much like the implication that 

much of their teaching was not relevant, but again it was not clear what should be done. The 

trouble was that many of us had gone to a university to study physics and had then returned to 

school to teach what we ourselves had been taught. We knew some physics, but little of the world 

outside the classroom. What teachers needed was help. 

It was for this reason that ASE set up its ‘Science in Society’ project in 1976. It was decided 

that in the first instance it should develop a one-year course suitable for 16 and 17 year old 

students as this could immediately be used in secondary schools as a General Studies course in 

the British sixth form system; there was a great virtue in getting something straight into the 

curriculum. This was the short term aim; the long term aim was to help teachers to become better 

informed so that at all levels they could show the relevance of their teaching to the world outside 

the classroom. Over 120 science teachers and more than 100 scientists, industrialists, engineers 

and professional people were involved in the development of the project; after three years of 

trials in fifty-two schools of various kinds, the material was published in 198 1 [ 1 I . 

The emphasis in ASE’s ‘Science in Society’ project is on help for teachers. There is already 

much evidence that teachers who have used the course find the experience influencing all the 

rest of their teaching. Science teachers certainly do need help and although ASE’s project is 

amongst the first to be developed, it is already clear that there wil be much similar work done 

elsewhere in the world in the next few years. The work being done on ‘Physics in Society’ in the 

Netherlands, for example, is considered later in thisvolume. 

346


ASE’s ‘Science in Society’ project starts with the students themselves, considering their own 

families, their own homes and their own environment. This leads to ‘Health and Medicine,’ a 

unit which begins factually and turns to questions of prevention rather than cure, personal 

responsibility for health, world health problems, the care of elderly and the dying, and the 

development of new drugs. An historical section brings out the way that science has contributed 

to society over the centuries. Health depends on ‘Food and Agriculture.’ The nature of food and 

the importance of nutrition and diet are linked with the problems of agriculture in the United 

Kingdom and in the world. This necessarily involves economic and social issues as well as scientific 

ones. The next unit concerns ‘Population’ and aspects of exponential growth. We have always 

studied exponential decay in our physiks - the discharge of a capacitor, the decay of a radiactive 

substance - but most of the world’s problems concern exponential growth, to which we have 

given little attention. The ‘Population’ unit also provides students with opportunities for 

extracting information from statistics, a skill needed by every future citizen as well as every 

future physicist, but one which is seldom practised in school. 

The ‘Energy’ unit deals with sources of energy (fossil fuels, nuclear energy, alternative sources) 

as well as the use of energy in our homes, in the United Kingdom and in the world. Issues of 

safety are discussed, as is the importance of energy in determining the quality of our lives. The 

‘Mineral Resources’ unit starts by considering material for the construction industry; this leads to 

the scientific, social and economic aspects of mining. Consideration of mineral resources leads 

to discussion and exercises on reclamation and recycling. The unit on ‘Land and Water’ is the last 

in the series of resources. The important unit on ‘Industry in the Economy’ examines the uses to 

which all the resources are put. It aims to promote a better understanding of the role of industry 

in society and the economic contribution which industry makes to the prosperity of a country. 

‘Facts’ is the title of a unit which offers aspects of the history and philosophy of science. It also 

includes reference to the presentation of facts, aspects of statistics and advertising. The final unit, 

‘Looking to the Future’, brings together the themes considered in the course, and concludes by 

asking fundamental questions about the quality of life and what young people expect in the 

future. 

The Teachers’ Guide provides the basis for the course. It shows a variety of ways in which this 

flexible material can be used. The Guide is supported by twelve student Readers, comprising 

ninety-nine papers and sets of data, under the titles: 

A Diseases and the Doctor 

B Population and Health 

C Medicine and Care 

D Food 

E Agriculture 

F Energy 

G 

H 

I 

J 

K 

L 

Mineral Resources 

Industry: Men, Money and Management 

Industry: Organisation and Obligation 

Nature and Science 

Science and Social Development 

Looking to the Future 

DECISION-M AKING 

A feature of the ‘Science in Society’ project is the series of decision-making simulation exercises 

[21 which are an integral part of the course and which involve the students in applying scientific, 

social and economic principles to real-life situations. They also develop analytical, decis 

and communication skills.New teaching techniques will inevitably be necessary in all 

relate science to the world outside the classroom and such decision-making games are likely to 

make an important contribution in the future. 

347


For example, it is easy for a teacher to lecture to students about power stations, about the 

differences between coal, oil and nuclear power stations and to discuss safety factors for each. 

But this amounts to the mere transmission of factual information without any involvement by 

the student, and although some of the facts wil be remembered by a few students, for the 

majority this is not a great educational experience. Better to divide the class into three SO that 

one group works on the coal-fired station, another on the oil-fired station and the third on the 

nuclear-powered station. The class might be provided with a map showing possible sites for the 

power stations and then it becomes a matter of competition between the groups to see which 

type of power station is to be built. Part of the value of such an exercise is that it is interdisciplinary. 

There are economic factors to consider and there are social factors as well as scientific 

ones, and of course safety factors wil also have to be considered by each group. A useful technique 

is to bring in a head teacher or a professor from a university as an adjudicator to whom 

each group puts its case. Young people always enjoy competition and the desire to win encourages 

them to find out information for themselves from the great wealth of material now available on 

these issues - and to find out for oneself is always a more rewarding and educative experience 

than listening to a teacher. Above all, this kind of decision-making exercise is fun and something 

enjoyed in this way by students is good education. 

ECONOMICS AND PHYSICS TEACHING 

Professor David Samuel of the Weizmann Institute wrote a year ago: ‘I think that the trouble 

with science in the first three-quarters of this century was that usefulness and money were 

considered not quite nice (as we were led to believe when I was at Oxford and later at Harvard) 

for young scientists at least. . . . The solution is, I think, to give school children a feel of what 

things cost - from bread and petrol to the cost of chemicals for an experiment in the lab. One 

does not need sophisticated economics to work out how long a bus driver has to work to pay for 

a pair of shoes or enough silver nitrate for a school experiment or to pay the salary of a teacher 

or lab assistant’. 

Surely the time has come to bring some economics into our physics teaching if we are to relate 

it to society. How electricity is distributed throughout a country is determined by economics and 

perhaps this should be considered as well as the details of the step-up and step-down transformers 

which have always been part of physics courses: it is the price of copper which influences the 

decisions which have to be made. 

The problems of central heating in our homes and the kind of insulation to be installed involve 

economics as well as physical principles, and all students (at least in countries where the heating 

of homes is important) wil need to make decisions about these issues later in life. 

Economics plays an important role in deciding about alternative energy sources. In the ‘Science 

in Society’ project there is a decision-making exercise which involves deciding which alternative 

energy sources should be used to meet the needs of the fictitious island of Elaskay off the west 

coast of Scotland. One part of the exercise involves calculating the cost of a unit of electricity 

(1 kWh) from different primary sources of energy. The students find that the cost of using tidal 

power, wind, hydro-electric power or burning peat ranges between 3p and 6p depending on the 

source and site chosen. However, they find that the cost of a unit of electricity produced from 

solar power is about &2 to &3, which is nearly two orders of magnitude greater. Experience of 

this exercise with adult physicists reveals that many of them are sadly unaware how uneconomic 

it would be to produce electricity in this way. An exercise of this kind is certainly applying 

physics to the needs of society. 

348

ENVIRONMENTAL SCIENCE, HEALTH EDUCATION AND OTHER DISCIPLINES 


It is not only economics which might be brought into our science teaching. Much development 

work has been done in recent years on Environmental Studies, on Rural Studies, on Health 

Education. An examination of such courses reveals how much worthwhile material has been 

produced. The environment and society are closely linked, and it is vitally important that young 

people should be aware that the use of scientific knowledge can be either beneficial or detrimental 

to the environment. It is sad that a large majority of school children do not study 

Environmental Science; most schools offer physics, chemistry and biology in some form, but to 

add Environmental Science as though it were a separate subject is just not feasible. It seems far 

more logical to incorporate much of the environmental science material into existing science 

courses. 

The same applies to health education, as also to nutritional science or engineering studies. 

In some countries, health education is provided as an alternative to physics, chemistry or biology 

for the academically weak students. This seems fundamentally wrong: we are all concerned with 

health, and education about it should be provided for all children. A place therefore should be 

found within existing science courses. 

WHAT MIGHT BE TAUGHT 

Of course, there is as great a need as ever to study Newton’s laws, to handle electromagnetic kits 

and to appreciate the evidence for energy levels, but perhaps the image of science would be 

improved if a little of the time spent on physics teaching could be given to examples of the ways 

in which physics has bettered the lot of mankind. Reference has already been made to health 

education, but the application of science to health and medicine over the centuries is such a 

powerful contribution to society that it must inevitably impress school children. 

It is not just a matter of showing the practical application of scientific principles, important 

as this is. Students have always studied Hooke’s Law for the stretching of materials and no doubt 

they should not cease to do so. But in society what matters is not the working of Hooke’s Law, 

but the point at which it breaks down, for this is what decides when a building or bridge will 

collapse. A slight but subtle change of approach is needed. Wires should still be stretched, but 

students should not be restricted to ‘verifying Hooke’s Law’ and told not to overload the wire 

‘for fear of damaging it’: the limitations of Hooke’s Law are as important as the law itself. This 

idea can be extended further from a special wire to materials in general. Pupils should be concerned 

with the materials which society needs and with their properties, for these are the daily 

business of the manufacturing and construction industries. 

However, the answer to what might be taught probably lies in Professor Vitta’s list quoted 

above. Most of the items in his list have links with physics and if only this were made apparent 

to school children it would show how powerful can be the contribution of physics to development 

throughout the world. It is, for example, energy which decides the level of productivity 

possible from land resources; energy requirements also influence both mining and industry. 

Aspects of communication and of transport could all be means of showing the relevance of 

physics to society and the environment. There is also the social impact of the electronics revolution, 

and no doubt electronics wil come to play an even larger part in science courses in the 

future. 

But it is not only the large scale issues that might be incorporated into the teaching. Mention 

might be made of Aunt Georgina, who decides to save energy by going to bed by torch light 

349


instead of switching on the electric light. It always astonishes pupils to calculate how much more 

this costs her. Another instructive calculation can be based on the fact that the total consumption 

of primary fuels in the United Kingdom was 1019 J per annum for a population of 55 

million. From these figures we find that the average consumption of energy per person per day 

is 500MJ. But a man can do a maximum of 3MJ in a day. So each person in the United Kingdom ~ 

has the equivalent of 167 slaves working for him. A further calculation can find what would be 

the rate of pay for a day’s work of 3MJ if it were rewarded at the same rate at which we pay for 

the electricity in our homes. The fact that the answer is so small reveals how cheap is the electrical 

energy we buy. That shows us that it is only because energy is so cheap that in the United Kingdom 

each person can have the equivalent of the services of 167. ‘slaves’. That, in turn, suggests a 

comparison with the plight of developing countries where such cheap electricity is not available. 

This is so fundamental to the progress of the developing world that it should be brought to the 

attention of all young people. Awareness of world problems is something that should be promoted 

through our teaching: how population continues to increase exponentially, how food production 

must also increase exponentially to keep pace with the population, how industrial output 

increases similarly, bringing a danger of exponentially increasing pollution, and how at the same 

time natural resources are decreasing. The detail of the Club of Rome’s report Limits to Growth 

[3] has been criticized, but the basic message is that you cannot indefinitely have exponential 

growth in a finite world: this is something which all young people can appreciate. The quality 

of life that wil be enjoyed by young people now at school depends on their facing the problems 

that beset us. To the solution of many of these problems science and technology have much to 

contribute, and as teachers it is our responsibility to make young people aware of the problems 

and of the need for solutions. Science teaching in the future must be seen in relation to the needs 

of society throughout the world. Then perhaps we will have a future fit for our children and our 

children’s children. 

REFERENCES 

1. 

2. 

3. 

ASSOCIATION FOR SCIENCE EDUCATION (ASE). Science in Society. London, Heinemann Educational 

Books, 1981. 

Details of the decision-making games can be obtained (and the games purchased from) the ASE, College Lane, 

Hatfield, ALlO 9AA, United Kingdom. 

The Limits to Growth: a Report for the Club ofRome’s Project on the Predicament ofMankind. New York, 

Universe Books, 1972. 

350

I 



H. EIJKELHOF AND J. SWAGER. 

One of the most recent trends in secondary education has been to pay more attention to the 

social aspects of science and technology. During the seventies, most courses developed in this area 

were either for lower ability groups in secondary schools or for general studies lessons. In the 

latter case, they do not form part of the science courses required for university entrance. This 

could create a situation in which students who know a great deal about science know less about 

the interaction between science and society than others who are less familiar with the science 

itself. The course which is described in this paper may be chosen as part of the national physics 

examination programme in the Netherlands for students who are preparing for entry into 

universities or colleges of higher education. 

After leaving primary school, one-third of the students go into some kind of vocational training; 

the majority, however, go on to a more general secondary education. Of these, only students 

following the so-called Voorbereidend Wetenschappelijk Ondenvijs (WO) are prepared for 

university entrance. In the first three years of VWO, the curriculum is essentially the same for all 

pupils. After this, pupils select seven subjects for the final examination, in the sixth year. The 

grade for each subject is composed of the results of two or more school examinations held during 

that year and that obtained in the national written examination (early May). Failure in more than 

two subjects generally means that the student must repeat the final year. 

The school certificate gives admission to universities. However, the student is not allowed to 

study in any department he or she chooses. Many university departments require a student to 

take specific subjects at VWO examination level. For example, physics must be included if he or 

she wants to study engineering, natural or agricultural sciences, medicine, dentistry, veterinary 

studies or physical education. About 60 per cent of students choose physics, often for this reason. 

Physics examinations are based on a national syllabus. A set core is studied each year, plus one 

topic chosen by the student and/or teacher. The topic requires 15 periods of teaching and is 

examined internally. Neither the present optional topics nor the core of the syllabus refer in any 

way to the social context of physics. 

In 1976, a group of physicists at the Physics Department of the Free University of Amsterdam 

decided to try to promote a course on ‘physics and society’ by developing a new optional topic 

for the VWO examination thereby ensuring increased recognition of the subject’s importance. 

35 1


Outside the examination programme, insufficient time is available to teach such a topic at an 

advanced level. It was also felt that 18 year-olds have a good grounding in physics and are mature 

enough to think in terms of the future of their society and the implications of technological 

development. It must be realized that teachers do not have much experience in dealing with the 

subject. Both content and method are new, and since it is an optional topic, there is no insistence 

that teachers teach it at this stage. In the future, such topics could be included in the core 

syllabus. 

AIMS AND CONTENTS 

There are no easy solutions to the problems mankind faces; every solution produces harmful side 

effects. Therefore, decisions have to be made at all levels: government, parliament, local council, 

works council, family. More and more people have the opportunity to participate in decisionmaking 

at one of these levels. They should be prepared for this, as making a choice in today’s 

problem areas is not an easy task. Education has an important role to play here, and especially 

science education, as so many problems have a scientific or technological content. Insight into 

the links between science and society is required and the course which will be described is meant 

to contribute to that. 

With thisgeneral aim in mind, we should be better prepared to look at the content of the course 

(table 1 and appendix) [ 11. The subject matter is divided into three parts. The text book starts 

by looking at a few problem areas where physics, technology and society interact. These are: 

energy, sound, transport and weapons. In each case, as much classroom physics is used as is 

considered suitable. The emphasis, however, is on the problems themselves rather than the 

physics, and attention is not diverted from the social, economic and political aspects. As these 

topics deal with controversial areas, care has been taken not to give prominence to the opinion 

of the authors by carefully ordering the arguments and by leaving the weighing of the arguments, 

as an exercise, to the students. 

The least cheerful chapter is that on weapons. It shows the highly advanced scientific and 

technological effort that is put into the development of modern weaponry. The arms race is 

described as well as endeavours to control it by negotiation. Some teachers hesitate to include 

it in the curriculum as they feel it puts a strain on supposedly ‘clean’ physics. The authors feel 

that reality demands that we treat this aspect of physics too. 

There is not enough time to deal with all four topics; thus it would be best to teach the energy 

topic and to choose one of the three others. 

The second part of the book is devoted to a more general treatment of the role of science in 

society. One chapter deals with the situation in Third World countries. We ask what type of 

science and technology are most suited to solving their problems. Intermediate technology is 

presented as one possible answer. Some examples in which physics plays a role are quoted. This 

chapter aims at giving the students the feeling that the world is larger than their immediate 

surroundings. The next chapter describes the historical development of the interaction between 

science, technology and society in the industrialized countries. This is illustrated by taking 

‘communication’ as an example. Next the control of the development of science and technology 

is looked at. Five different views are outlined on the causes of the negative effects of sciencebased 

developments in society, from Marx and Roszak to Galbraith and the modern Christiandemocrats. 

The last part of the text deals with the future. Some methods of technological forecasting are 

described. It is made clear that at each point in time several choices are possible and that their 

352


consequent long term effects might be quite different. Finally, two alternative energy scenarios 

are discussed. One is a WAES-scenario which assumes an economic growth rate of 3 per cent per 

annum. The other one takes the line that further production growth in the Netherlands is not 

sensible. This produces energy savings which could bring the energy consumption in the year 

2000 back to 68 per cent of the 1975 level, while the first scenario results in 235 per cent of this 

level being reached in the year 2000. It is shown that much depends on the way of life people 

are prepared to accept. 

Each chapter contains exercises and references to books and articles. A list of thirty-eight 

addresses is included to encourage students to obtain more information from government circles 

and private organizations. 

TABLE 1. Content of the course book ‘Physics in Society’ 

Chapter 

No. of pages 

1. Introduction 

li 

2 

2. Energy 

40 

3. Sound 

choice of 30 

4. Transport 

one chapter 18 

5. Weapons 

38 

6. Science and technology in the developing countries 

16 

7. The spiral of science, technology and society 

26 

8. Physics in the future 

17 

THE DEVELOPMENT OF THE CURRICULUM 

In the first stage of the project, three draft texts were written by members of the project group. 

After an announcement in teachers’ journals, about thirty teachers showed interest in discussing 

the drafts. Several meetings were devoted to this and twenty teachers were willing to try out the 

material in their classes in the spring of 1977. At that time, the topic could not be included in 

the examination programme. After evaluation of the trials and discussions on newly written 

chapters, it was decided to ask permission for nineteen schools to include the optional topic in 

the examination at VWO level in 1979. Permission was granted by the Secretary of State for 

Education and 844 students included this topic in their exams. 

So thirty-one teachers were able to get experience with the topic. A teachers’ guide was 

written for them. It included information on literature, films,objectives, teaching methods and 

ways of evaluating students’ progress. The teachers were free to choose appropriate teaching and 

evaluation methods. Not surprisingly there were a great variety of these. Some preferred to stick 

to the texts; others used the book as a starting point for students’ investigations. When it came to 

testing some teachers used the question format to which the students were accustomed; others 

marked assignments or oral presentations. This freedom was given with the purpose of finding 

original ways of approaching the topics. At the same time, all concerned shared the view that no 

ideal method exists as schools, teachers and classes vary considerably. After a further announcement 

in teachers’ journals, forty-seven schools with seventy teachers and 1800 students obtained 

permission to include the topic in the 1980 examinations. 

With so much support, the project group decided to initiate the procedure for the inclusion 

of ‘Physics in Society’ (Pins) as an optional topic in the regular examination programme. It is 

expected that eventually, all VWO-schools wil be allowed to teach ‘physics in society’ as part 

of the official programme. 

353


TEACHING METHODS 

Because the Pins subject matter differs greatly from usual physics, new teaching methods were 

developed. The freedom of the teacher to choose his own method resulted in a great variety (see 

table 2). In practice different considerations play a role in the choice. The most important are: 

which aims are emphasized; how much time is available; the experience of the teacher in applying 

unusual teaching methods; and the atmosphere in the classroom. 

TABLE 2. Teaching methods 

1. lecture 

2. class discussion 

3. commenting on ‘proposals’ 

4. groups working independently 

5. investigation of literature 

6. group presentation 

7. assignment 

8. interviews 

9. inviting experts 

10. simulation games 

1 1. practical work 

12. audio-visual aids. 

Our information on the teaching methods used is based on interviews with teachers, on discussions 

at teachers’ conferences and on our classroom observations. Some of the more unusual 

methods are discussed below. Commenting on various proposals is one method of structuring 

classroom discussion. Groups of students are asked to formulate proposals, e.g. on energy policy, 

and to write comments on those of their peers. Discussions are usually very lively. For a literature 

investigation the students can collect the material themselves. To avoid wasting time while 

waiting for the material, collecting would sometimes start months before the actual lessons take 

place. The results of the investigation might be presented to the class by the students (group 

presentations). The same material might also be used as the basis for an assignment. It seems to 

be difficult for individual students to deal with topics in both the areas of physics and society. 

The assignments often turn out to be purely physical or purely social. 

The independence of the thinking of the students depends strongly on the working methods. 

Compared with the limited independence in lectures and classroom discussions, there is far 

greater freedom associated with a literature investigation or an assignment; there the students are 

able to decide the topic of investigation and to collect the material themselves. Then their 

involvement is far greater. They appear to take more initiative at interviews and on excursions, 

especially within the framework of group assignments. 

Sometimes classroom discussions suffered from poor involvement. When the discussion was 

structured (e.g. by the presentation of a proposal) or preceded by a controversial film, the 

participation was much better. Simulation games about the siting of a nuclear power station were 

played with great enthusiasm. In general, involvement increases as students are able to choose 

between real alternatives. As a consequence of the specific character of Pins and the variety of 

working methods, the role of the teacher changes, becoming that of an activating, stimulating 

guide. Not surprisingly, teachers felt less safe than usual: in controversial matters, their opinion 

is no longer taken for granted, it is a point of view no more valuable than those of the students; 

354


furthermore, students are studying subjects with which the teachers are not always familiar. As 

always, the atmosphere in class determines the success or failure of a particular teaching method. 

For example, group presentations are doomed to failure if the class is not willing to listen. Switching 

to a different method would be the only possible solution. 

The limited time available plays an essential role in lessons. As affective aims are pursued 

among others, it is necessary to assimilate the framework within the fifteen lessons available for 

an optional topic. Therefore, teachers were eager to find teaching methods which fitted into the 

time available. They concluded that assignments are suitable only when the topic and its limits 

are sharply defined. Some teachers created additional time by co-operating with colleagues of 

other disciplines. A majority of the teachers stated in a questionnaire that they would prefer to 

teach Pins in form 5 because of examination stress in form 6. 

EVALUATION 

As an optional topic in the physics examination, Pins is evaluated in school examinations. The 

most commonly used method of evaluation is by written examination and assignments. In 

addition, oral examinations, essays and group presentations are used. The criteria by which the 

work of the students would be assessed are discussed in lessons before the examination. In some 

cases, the teachers with no Pins experience have difficulties with the objectivity of their judgement. 

More experienced teachers would not have these problems. Their advice would be to ask 

a colleague to help formulate clear criteria, which can then be explained to the students. 

THE STUDENTS’ OPINION 

Table 3 shows the students’ opinions on the course. Their opinions are in general very favourable. 

Students believe that physics plays an important role in society. They wish to know more about 

this and acquire more insight into the relationship between physics and society. To them, these 

relationships are more important than some of the relationships between physical quantities 

which can be expressed in formulae. They appreciate facts and figures which can be used to 

support or to refute arguments. These facts and figures tend to be missing in the discussion in 

other classes. 

The enthusiasm of students is partly due to the choice of teaching methods which encourage 

participation and in which students feel more involved. It also has to do with the themes, which 

seem to be more attractive and less remote than more conventional .themes in physics. Table 4 

shows how students appreciate the various topics which are dealt with in the course. Energy was 

the most popular chapter for both boys and girls, in both interest and importance. From our 

discussions with students, we learned that they are especially happy with the treatment of the 

controversial topic: nuclear energy. Seldom do they come across careful ordering of arguments 

for and against. The next most popular topic is weapons. Both boys and girls found it almost 

as important as energy, though in the rankings based on interest we found the boys slightly more 

interested in this topic than the girls. The latter were more interested in sound and in developing 

countries. The least popular topic is the ‘spiral of science, technology and society’, which is due 

to its abstract character. In the latest revised edition of the text book, this was taken into 

account and the new chapter deals with the topic in a more structured way. 

355


TABLE 3. Students’ opinions of the come 

Instrument: questionnaire among the 844 students of the 1979 examination, 54 per cent responding (314 boys, 

1 /4 girls) percentage response 

Yes yes? no? no 

1. Pins should be permanently 

incorporated in the physics 56 28 7 9 boys 

curriculum 75 15 7 3 girls 

2. Pins is more interesting 51 27 10 12 boys 

than conventional physics 58 27 9 6 girls 

3. I enjoyed the Pins lessons 54 25 8 13 boys 

58 24 11 7 girls 

4. I intend to read more about 23 38 18 21 boys 

the Pins topics in the future 17 52 17 14 girls 

yes = Iagree 

no = I do not agree 

yes? = although I’m not sure, I do agree 

no? = although I’m not sure, I do not agree 

TABLE 4. Students’ opinion about specific PinS-issues* 

chapter 

Percentage of students that found the chapter: 

interesting important dull difficult full of generally 

information known 

boys girls boys girls boys girls boys girls boys girls boys girls 

2. Energy 97 96 97 100 15 10 9 13 88 91 35 20 

3. Sound 87 100 88 96 19 17 11 2 81 89 21 17 

4. Transport 95 97 90 97 15 3 5 3 84 88 42 12 

5. Weapons 92 89 94 100 13 14 17 29 82 100 25 6 

6. Developing 

countries 82 92 88 93 31 15 4 0 59 78 36 24 

7. Spiral 63 72 72 78 47 44 35 22 57 69 15 3 

8. Future 88 86 90 100 29 9 14 14 62 82 29 5 

*Students could answer questions about the chapters on a 6-point scale: 

yes! = I agree very much 

yes = I agree 

yes? = although I’m not sure, I do agree 

no? = although I’m not sure, I do not agree 

no 

I donot agree 

no! = I do not agree at all 

The percentages quoted are the sum of the first three categories. 

356


TABLE 5. What did you learn most of all in the Pins-lessons? 

a. 

b. 

C. 

d. 

e. 

f. 

g. 

h. 

specific knowledge* (e.g. ‘windenergy’) 

the connection between physics and society 

(e.g. ‘I never noticed before that physics 

has anything to do with society’) 

the application of physics 

(e.g. ‘it is good to see what they do in 

practice with all these theories’) 

the change of image of physics 

(e.g. ‘physics is not just making theories 

in isolated laboratories’) 

negative answers (e.g. ‘nothing at all’) 

a specific awareness 

(e.g. ‘energy saving is necessary’) 

skills (e.g. ‘to make your own investigation’) 

uncategorized (e.g. ‘probably a lot’) 

22 

18 

7 

8 

8 

7 

5 

25 

100 

*More than half of the answers are energy-related. 

Boys have a better knowledge of each topic beforehand than girls. This might have to do with 

the number of them who read newspapers: 85 per cent of the boys indicated that they read a 

newspaper daily or more often, whilst only 58 per cent of the girls did. 

Of course not all students are in favour of having physics and society as part of their education. 

Usually opponents feel insecure because of the different character of the topic. In most cases, 

teachers tried to resolve this problem by clarifying such issues as the basic requirements and 

methods of assessment. They explained, for instance, that it was not the opinion itself but the 

facts and the consistency of the arguments which were presented which would be judged. After 

the examinations, hardly any dissatisfaction with the assessment was apparent. 

The students were asked: what did you learn most of all in the Pins lessons? Table 5 shows 

their answers. Many students appear to be impressed by the relation between physics and society. 

The answers show clearly that students are quite impressed by the influence of physics upon 

society and less by their mutual interaction. This may be due to the limited number of periods 

(fifteen); perhaps there is not enough time to communicate a profound insight into the spiral 

of science, technology and society. 

Pins may change the students’ image of physics; they mention for instance the importance of 

the relationship between faith, political views and science. 

IMPACT OF THE COURSE 

Although the course is a small part of their education, fifteen periods compared to the hundreds 

of other physics periods, the impact of the course is greater than this allocation would indicate. 

In the trial schools, teachers reported the use of parts of the text in other classes. Having experi- 

357


ence in forms 5 and 6 of VWO, they were inclined to pay more attention to ‘physics and society’ 

aspects in all of their teaching. In a couple of schools, co-operation with teachers of other 

subjects was established. Many school libraries were supplemented with books and magazines 

covering the topics. Several teacher training colleges are using the text book as an introduction 

to the subject which they study at a more advanced level. 

In 1979, the two main conferences for physics teachers in the Netherlands paid some attention 

to physics and society and its relevance in education. In the summer, 180 teachers met for two 

days in Amsterdam to study teaching methods and materials in a large number of ‘workshops’. 

Many of the delegates had no previous experience of the teaching of ‘physics and society’. In 

December, 220 teachers met in a two-day conference on trends in physics teaching. Virtually 

all of those attending supported the idea that the social aspects of physics should receive more 

attention in education in the next decade. Several curriculum development projects already show 

signs that this wil happen. 

CONCLUSION 

Making changes in physics teaching is not easy. Academic influences are strong; teachers are 

used to conventional content and method, and are, above all, busy people; the training of new 

teachers wil bear fruit only in the long run; examinations are a stumbling block for many and 

stimulate competition rather than co-operation; and gaining the acceptance of a new examination 

syllabus by all the authorities concerned takes perseverance and patience. 

The other side of the coin is less bleak. The Pins project has proved that an encouraging 

number of physics teachers in the Netherlands are willing to start closing the gap between physics 

and society. They prefer to spend time revising their teaching of physics rather than sticking to 

the old ways. Many have said that they would never return to teaching physics without teaching 

it in its social context. 

The project also showed that a small project, with few staff and little money, covering only 

part of the physics syllabus, can have a great effect if it hits upon the interests of enthusiastic 

teachers. 

However, we must stress that only students of a particular age and ability range were involved. 

More experience is required regarding other age groups and ability ranges. The future requires 

material in which physics and society are integrated rather than a conventional syllabus with an 

option tacked on. 

REFERENCES 

1. EIJKELHOF, H.M.C.; BOEKER, E.; RAAT, J.H.; WUNBEEK, N.J. Physics in Society. Amsterdam, VU 

Boekhandel, 1981. (In English.) Distributed in the United Kingdom by SISCON (c/o Department of Liberal 

Studies in Science, University of Manchester) and elsewhere by VU-Bookshop, P.O. Box 7161, 1007 MC, 

Amsterdam, The Netherlands. 

2. The main example is the PLON-project at the University of Utrecht. PLON is concerned with developing 

and evaluating new teaching materials and methods for general secondary education. Some important aims 

are to relate physics to student-experiences and to developments in society. 

The authors wish to thank Professor E. Boeker and Professor J.H. Raat for their kind co-operation. 

358


APPENDIX 

Detailed contents of the course Physics in Society. 

Energy 

- energy and physics. 

- energy consumption in the Netherlands and elsewhere ; advantages and disadvantages of fossil energy sources 

and nuclear energy. 

- some types of nuclear reactor, breeder reactor. 

- alternative energy sources. 

- saving energy. 

- energy policy. 

Sound 

- physics of sound levels (decibel, influence of distance, measurement). 

- noise in different sectors of society. 

- measures against noise. 

Transport 

- energy consumption of means of transport. 

- motors and air pollution. 

- traffic safety devices. 

- development of private and public transport in the Netherlands. 

Weapons 

- physics of fission and fusion bombs. 

- tracking systems for weapons (air, sea). 

- history of nuclear armament. 

- armament race and peace initiatives. 

Developing Co un tries 

- energy in the Third World. 

- comparison of traditional and advanced technologies. 

- role of appropriate technology. 

Spiral of Science, Technology and Society (STS) 

- scientific method. 

- historical development of STS, contemporary situation. 

- views on control of science and technology. 

Future 

- methods of forecasting. 

- comparison of two energy scenarios. 

359


Appropriate Technology 

M.K. McPHUN. 

Many people have no idea at all of what Appropriate Technology means, and others have the 

quite mistaken idea that it refers to a second-class technology for those unable to afford the real 

thing. Yet who would choose to use or teach any form of technology that they knew to be 

inappropriate? The question immediately arises as to whom or what it is appropriate, and this 

needs answering in depth. 

In the following I shall devote the first section to defining what is meant by Appropriate 

Technology, and attempt to show that its application should be universal. I shall then consider 

how its underlying concepts might be taught in the school. 

WHAT IS APPROPRIATE TECHNOLOGY? 

The use of technology is a major factor in industrial development, so it is to the industrially 

developed world that we must look first. It is there that at present most of the world’s energy 

and resources are being consumed, and it is there that an extensive critique of technology and 

its consequences has evolved. 

For a long period, ever since the start of the industrial revolution in the United Kingdom, 

technological developments were accepted without question as inevitable. ‘You can’t stand in the 

way of progress’ was a saying generally accepted, without any attempt being made to define 

‘progress’. The ‘progress’ referred to was in fact some development in technology, or a social 

change consequent upon that development. In retrospect it is clear that often the progress was 

negative in terms of the well-being of the human race. The challenge now is to define ‘progress’ 

taking into account all the factors, social and environmental, as well as technological. 

This critique of technology has grown up under the umbrella term Alternative Technology, 

outside of the public institutions and government. It has taken some years for it to gain any 

respectability, but now some countries have got as far as requiring - by law - that environmental 

impact analyses be made, to discover the likely long-term effects of proposed new technological 

developments. 

360

Appropriate technology 

The visible effects of pollution from industrial processes played a large part in bringing about 

this change of attitude, and the scene was set by the publication of Silent Spring by Rachel 

Carson [ 11 in 1970. Local pollution, often clearly evident in extreme forms such as coloured, 

smelly water in ditches, had been tolerated in many industrial areas since the start of the industrial 

revolution. It was the global effects of substances like DDT reaching far away from their areas 

of application that awakened the consciousness of ordinary people, who were then able to see 

the existing pollution they were living with. 

The publication of Limits to Growth by D.H. Meadows et al 121 in 1972 set out computer 

predictions of the effects on the world population, of continuing the current trends in the 

consumption of energy and other resources. They clearly showed the need for drastic changes 

in the application of technology if civilization is to survive the next 100 years. Most people in 

positions of responsibility didn’t believe these predictions, and little was actually done. It took 

the drastic increase in the price of oil in 1973 to spur the industrjal nations into efforts to curb 

the waste of energy. That which repeated appeals to the conscience for the well-being of future 

generations could not achieve, was brought about by being hit in the pocket. In 1973 Schumacher’s 

book Small is Beautiful C31 crystallized many of the faults of modern technology, and made 

many people aware for the first time that alternative approaches were possible. 

How is it that there can be such a distinction between the acceptability of a device used today 

and its long-term usefulness in relation to a future that will be increasingly short of resources? A 

prime reason is that minerals and fossil fuels have traditionally been treated and priced as consumables, 

whereas in fact they are finite and would more appropriately be treated as capital. 

The underpricing of energy has led to the use of many inappropriate technologies. Even today 

natural gas is often flared off from oil wells because it is too expensive at current prices to transport 

it to where it can be used. Future generations without the benefits of natural gas wil hardly 

regard this current waste as justified. The human race has a very limited capacity for viewing 

present practice dispassionately and needs a succession of prophets to open its eyes to its shortcomings. 

In times past, slaves were an accepted part of society. 

The shortcomings of much of modern technology can be summed up in the characteristics: 

unsustainable, unfair and unpleasant. Unsustainable, because this world cannot keep up supplying 

energy and mineral resources at the rate at which they are being used, and cannot continue 

to absorb pollution at the rate it is being created. There is a definite time limit to carrying on like 

this. Unfair, because of the way the world’s resources are being shared out, with 30 per cent of 

the world’s population consuming 80 per cent of the total energy, and with a similar picture for 

other resources. There is no way in which the developing nations could partake of the world’s 

bounty on the same scale as the developed countries already do; there is not enough to go round. 

The recent report of the Brandt commission, North South - a Programme for Survival 141, has 

shown that even from the viewpoint of conventional economics, it is in the self-interest of the 

developed world to share out resources more fairly. Unpleasant, because of the side-effects of 

much of technology: the effects of pollution, industrial diseases, poor working conditions, 

factory farming, de-skilling of jobs, concentration of populations in large cities and structural 

unemployment . 

The positive response to these three characteristics has been the creation of three spheres of 

activity which can conveniently be classified as Environmental Alternative Technology, Intermediate 

Technology and Political Alternative Technology. In practice they often become closely 

interlinked, and this is a frequent source of confusion to the casual observer, so I will first deal 

with each in turn before considering how they may interact. 

36 1


1 Alternative Technology 

This includes work on the so-called “soft’ technologies of renewable energy supplies such as solar, 

wind and water power. Techniques of energy conservation have a very important place, as do 

methods of utilizing fossil fuels more efficiently such as combined heat and electricity generation 

schemes. It includes techniques for recycling material resources, from recycling waste paper, 

through the production of methanol from organic wastes, to the adaptation of scrap vehicle 

parts to other uses. Forming an important sector are techniques of organic food production 

which eliminate the need for inputs of artificial (chemical) fertilizers, pesticides and fungicides, 

and achieve high yields through the recycling of organic matter to the land. 

The scale of application of this type of Alternative Technology may vary widely. The generation 

of electricity from the waves or tides is unlikely to be practicable except on a very large 

scale, and financed therefore only by governments. In contrast, the power of the sun can be 

harnessed on an individual basis, though large-scale applications are possible here also. 

A recurring theme of Alternative Technology is the use of combinations of techniques, unlike 

conventional technology which has tended to be highly compartmentalized. Thus a small fishfarming 

scheme may make use of solar heating to heat the ponds, which will be highly insulated 

to conserve the heat; a wind pump circulates the water to provide oxygenation with a backup 

of biological techniques for purification; pond water rich in nitrates is used to fertilize the 

organic vegetable gardens on the same site. Another example is the house having its own energy 

supplies; it is well-insulated, and a wind generator drives a heat pump to recycle heat from waste 

water and ventilation air. 

Alternative Technology is any technology that is an alternative to those that exploit people 

or the environment to the detriment of either. 

Intermediate Technology 

This is concerned with raising the standards of the poor in developing countries by the introduction 

of technology intermediate between the primitive and what is unaffordably or unjustifiably 

elaborate. It was introduced as a response to the adoption of inappropriate technologies that had 

caused widespread unemployment, an overcapacity of products people could not afford to buy, 

and an increasing dependence on the import of raw materials and energy. Schumacher in Small is 

Beautiful [31 made out the case for an Intermediate Technology in which the highest priority 

should be to maximize work opportunities for the unemployed and underemployed, rather than 

to maximize output per person. The Intermediate Technology Development Group (ITDG), 

started by Schumacher in the United Kingdom seeks to devise and promulgate suitable techniques 

to achieve this. Often this can be achieved simply by technology transfer, that is, introducing 

known techniques from one area to another where they are unknown. 

An example of technology transfer is the making of hand-thrown bricks from local clay using 

the simplest of machinery which can in turn be made by existing rural craftsmen. The introduction 

of this technique into countries with no indigenous brick-making industry has resulted in an 

improvement in housing standards, more employment in rural areas and a reduction in imports. 

It is significant to note that, with the drastic rise in unemployment in the United Kingdom there 

has been a resurgence in the making of hand-thrown bricks there also. ITDG is now also active 

in promoting the principles of Intermediate Technology as a cure for some of the bad effects of 

technology in the developed world, as further investment in high technology in a resource-limited 

society inevitably results in further unemployment. 

362

Political Alternative Technology 

Appropriate technology 

This is concerned with alternative ways of organizing society, the way people live, their patterns 

of work, the structure of industry and how they are housed. It is also concerned with education, 

health care and financial institutions. In many cases Political Alternative Technology is a rediscovery 

of the relevance to the present day of movements from decades, or even centuries ago. 

Thus Kropotkin’s Fields, Factories and Workshops [5] first published in 1899, has been widely 

quoted as containing the answer to many of the ills of present-day industrial society, and was 

republished in 1974. 

The scale of application here may vary widely also. Take for example the participation of 

workers in the management of industry. We have, on the one hand, the participation of ‘worker 

directors’ on the boards of directors of a large company which is in all other respects quite 

conventional. On the other hand, there are large numbers of small worker-cooperatives being set 

up in the United Kingdom in which the firm is entirely owned by the people working in it. 

The formation of experimental communities for people to live and work in has been a reaction 

against the anonymity of the large city with its accompanying waste. The degree to which such 

communities share buildings, facilities and possessions varies widely, as does the scale of the 

enterprise. This may vary from a number of people sharing an urban house, to the establishment 

of a complete ‘co-operative village’ where most people live in their own houses but work parttime 

in the village industries and part-time in growing food. 

How these Interact 

There are no firm boundaries to the above fields, and they wil frequently be combined. Thus 

it is no accident that many of the small worker co-operatives in the United Kingdom are concerned 

with retailing organically grown wholefoods. People living in communities are likely to be 

engaged in recycling, organic techniques of food production, or generating their own power. 

Techniques from the field of Environmental Alternative Technology such as improved simple 

designs of windpumps have been applied successfully in the Intermediate Technology field, and 

here many of the ideas of Political Alternative Technology are relevant also. 

All the above spheres are embraced by the term Appropriate Technology, which includes also 

conventional ‘high’ technology where that is appropriate. High technology is characterized by 

complex expensive processes requiring a large capital outlay per person employed. The essence 

of an Appropriate Technology is its fitness for local function, rather than for universal application, 

and its appropriateness must be judged taking into account all the relevant factors, social 

and environmental as well as technical. 

Some things that Appropriate Technology is not: it is not a second-hand technology; only the 

best is good enough. But in a given situation the best is probably not the most elaborate or 

expensive, and it may be very simple and cheap. It is not necessarily easy or obvious, and wil 

often call for more creative and inventive skill than the use of an inappropriate technology. It is 

not a well defined discipline, but because some relevant factors will be non-technical, the judging 

of appropriateness is essentially interdisciplinary in character. 

Whilst any particular Appropriate Technology has an essentially local function, the concepts 

underlying Appropriate Technology have universal application. We are now in a position to see 

how these concepts can be brought into our teaching. 

363


TEACHING APPROPRIATE TECHNOLOGY 

There are two risks that accompany the teaching of science at school. The first risk is that pupils 

wil be so captivated by the fascination and challenge of the subject that they regard pursuit of 

the scientific discipline as an end in itself and will in future not care to what their work is applied. 

This has been the case with the majority of science and technology entrants to universities in the 

past, and is an important contribution to the fact that at present 40 per cent of all the world’s 

scientists and engineers, are working directly or indirectly on weapons of destruction 161. The 

second risk is that as a reaction to the first, other pupils wil reject all technology as being 

irrelevant to the real needs of humanity. 

I have written elsewhere on how Appropriate Technology can be introduced at degree level 

[ 71 but that is starting too late. It is only by introducing its concepts as part of the background 

of school science teaching that the above risks can be avoided. 

It would be most inappropriate of me to attempt to give a detailed plan of how you should 

bring Appropriate Technology into your teaching. The circumstances of readers wil vary so 

much in so many ways - the local climate, the degree of development, the money and equipment 

available, the presence or absence of local industries or farming - these and other factors 

must influence the approach used. It is possible however, to lay down the following guiding 

principles that should form assumptions underlying all the teaching. 

1. Technology should be appropriate. Scientists and engineers should be primarily concerned 

with the social objectives, and they should acquire and use technical skills in order to achieve 

them. 

2. In judging appropriateness, or fitness for purpose, factors other than technical ones must 

be taken into account. Such factors may be geographic (very limited water supplies), economic 

(the need to save foreign currency by limiting imports of steel), ecological (clearing the hedges 

will destroy the habitat of beneficial wild life), political (the region has aspirations of economic 

independence), or social (the land is owned by absentee landlords). These examples could be 

multiplied endlessly, and furthermore they often interact. 

3. We cannot escape the link between judging appropriateness and the need to make moral 

judgements. For example the introduction of capital-intensive equipment into a community 

where everyone is self-employed can result in a complete change in the social structure, with 

most people becoming employees. 

4. The solution to a problem may not be technological. Some of the most dramatic increases 

in food production have been obtained by changes to the local social system to ensure that the 

people growing the food obtained personal benefit from increasing their output. This succeeded 

where the introduction of new grain varieties had failed. 

5. High or new technology may not be appropriate. For example, where there is a surplus 

of labour, a simple technology that uses it more effectively is more likely to be appropriate than 

one which replaces labour by machines. 

6. The user of a piece of equipment or a technique must be taken into account. Intermediate 

Technology equipment for growing food in one region failed to be socially acceptable because all 

the food growing there was done by women, but only the men were consulted. 

Given that school teachers make assumptions such as the above, they wil influence the atmosphere 

in which their pupils work and mature. These assumptions wil influence the way subjects 

are presented regardless of what appears in the syllabus. Examination questions can be made 

more relevant to the local situation. 

364

Appropriate technoIogy 

Project work is a most fruitful way of involving pupils in Appropriate Technology. However, 

a glance through the above list of assumptions makes clear that such project work is essentially 

interdisciplinary in nature. Is there co-operation in your school between the physics and craft 

staff, or between chemistry and geography? If not, then an Appropriate Technology project 

could be the means of bringing it about. 

The first requirement for undertaking any project work at school is a certain amount of confidence 

on the part of the teachers involved. For the teacher who is used to working to a set 

syllabus and adhering closely to standard textbooks, taking the. plunge into leading an openended 

project can be a daunting task. Fortunately there is now a way to gain this confidence, and 

that is by starting with the Science in Society course materials described in an earlier chapter. 

The teachers taking part in the pilot trials of this course witnessed to how profoundly it had 

affected their teaching in all subjects. 

The subject of suitable project work must depend on local circumstances. The design of equipment 

for the school is a fruitful field. If you are studying energy, examine how the school is 

heated (or cooled) and where the losses are. How could the design be changed to save fuel? Could 

the utilization of the buildings be changed to save fuel? If so, what would be the social effects? 

Many schools are in rural areas in which food production plays a major part in the homes of 

most pupils, and here many projects are possible. What happens to the waste products? Could 

they be utilized more effectively, and for this would they require processing in some way? If 

so, the design and construction of some suitable equipment (e.g. a man-powered compost 

shredder) could be undertaken. 

Another source of projects is the wide field of materials substitution. Take a product that is 

widely used locally and is imported, either into the country or into the area. How could it be 

made locally from local materials? This study could be tackled in three ways, first, following a 

similar method of construction and principles; second, by analyzing its function - what does it 

have to do? is it possible to think of a different way of fulfilling the function easier using local 

materials? and third, go back a further stage and examine why it is needed. Could the system 

within which it is used be changed to a more appropriate one for the local circumstances? If so, 

what are the social constraints preventing this? 

Much can be learnt from the efforts and experiences of other people, and any school wishing 

to do projects in Appropriate Technology would find Appropriate Technology, the journal 

published by the Intermediate Technology Development Group [ 81 , most useful. It contains very 

practical articles about Intermediate Technology projects in developing countries. 

I have tried to make out a case for making all technology appropriate, and for introducing its 

concepts into school teaching. Technology which has the effects of making the rich richer at the 

expense of making the poor poorer can never be called appropriate. It is people who govern the 

paths taken by technology, and it is up to us to introduce our future decision-makers to the 

concepts of appropriateness sufficiently early - whilst they are at school. 

REFERENCES 

1. 

2. 

3. 

4. 

CARSON, Rachel. Silent Spring. London, Penguin, 1970. 

MEADOW, D.H. et al. The Limits to Growth: A Report for the Club ofRome’s Project on the Predicament 

of Mankind. New York, Universe Books, 1972. 

SCHUMACHER, E.F. Small is Beautiful. London, Abacus, Sphere Books Ltd., 1974. 

North-South: A Programme for Survival (The Brandt Report). Cambridge, Mass., MIT Press; London, Pan 

Books Ltd., 1980. [The Report of the Independent Commission on International Development Issues.] 

365


5. KROPOTKIN, P.A. 1899. Fields, Factories and Workshops Tomorrow. New ed. Edited by Colin Ward. 

London, Allen and Unwin, 1974. 

6. THRING, M.W. The Engineer’s Conscience. London, Northgate, 1980. 

7. MCPHUN, M.K. Teaching Appropriate Technology in the Engineering Degree. Appropriate Technology, Vol. 8, 

No. 2, September 1981. 

8. Appropriate Technology. Intermediate Technology Development Group, 9 King Street, London WC2E 8HN, 

United Kingdom. 

366

Contributors 

Albert A. BARTLETT, University of Colorado at Boulder, United States. 

Antonella BASTAI PRAT, Liceo Classic0 Massimo D'Azeglio, Torino, Italy. 

Claudio Zaki DB, Institute of Physics, University of Sa"o Paulo, Brazil. 

Ronald D. EDGE, University of South Carolina, United States. 

Harrie EIJKELHOF, Natuurkundig Laboratorium, Vrije Universiteit, Amsterdam ; PLON, Lab. Vaste Stof, University 

of Utrecht, Utrecht, The Netherlands. 

Professor Djibril FALL, Department of Physics, University of Senegal, Dakar, Senegal. 

John M. FOWLER, Director of Special Projects, National Science Teachers' Association, Washington, D.C., United 

States. 

A.P. FRENCH, Physics Department, Massachusetts Institute of Technology, United States; Chairman of the 

International Commission on Physics Education. 

Nabil H.A. GALIL, Expert in Science Curriculum Development, Ministry of Education, Qatar. 

Heleny Uccello GAMA, Institute of Physics, University of SSo Paulo, Brazil. 

Edith GUESNE, LIRESPT, Universiti de Paris VII, France. 

T.D.R. HICKSON, The King's School, Worcester, United Kingdom. 

Kunio HIRATA, Faculty of Education, Yamanashi University, Japan. 

F.J. KEDVES, Institute for Applied Physics, Kossuth Lajos University, Debrecen, P.O. Box 2, H-4010, Hungary. 

L. KOvAcS, Landler Jen6 Gimnizium, Nagykanizsa, H-8800, Hungary. 

P. KOVESDI, Department of Physics, Juhisz Gyula Teachers' Training College, Szeged, P.O. Box 396, H-6701, 

Hungary. 

John W. LAYMAN, University of Maryland, United States; President of the American Association of Physics 

Teachers. 

John L. LEWIS, O.B.E., Malvern College, United Kingdom, Secretary of the ICSU Committee on the Teaching of 

Science, Director of the Association for Science Education's Science in Society Project. 

Sandra MAGRINI, Institute of Physics, University of Siio Paulo, Brazil. 

M.K. MCPHUN, Department of Engineering, University of Warwick, United Kingdom. 

G.A. MESYATS, Siberian branch of the USSR Academy of Science, Tomsk, USSR; member of the International 

Commission on Physics Education. 

D. NACHTIGALL, University of Dortmund, Federal Republic of Germany. 

Jon OGBORN, Centre for Science and Mathematics Education, Chelsea College, London, United Kingdom. 

Alfred PFLUG, Institut fur Theoretische Physik, Universitat, Wein, Vienna, Austria. 

PHYSICS WORKGROUP OF THE SCIENCE EDUCATION CENTER, University of the Philippines. 

Peter E. RICHMOND, Department of Education, University of Southampton, United Kingdom. 

Dr. H. Joachim SCHLICHTING, University of Osnabruck, Federal Republic of Germany. 

Roman U. SEXL , Institut fur Theoretische Physik Universitat Wein, Vienna, Austria. 

B. SHARAN, Department of Education in Science and Mathematics, National Council of Educational Research 

and Training (NCERT), Sri Aurobindo Marg, New Delhi 110016, India. 

Johan SWAGER, Natuurkundig Laboratorium, Vrije Universiteit, Amsterdam; Albanianae Secondary School, AS 

Alphen aan den Rijn, The Netherlands. 

Charles A. TAYLOR, Physics Department, University College, Cardiff, Wales, United Kingdom; Chairman of the 

ICSU Committee on the Teaching of Science. 

Joseph M. YAKUBU, Department of Science Education, University of Cape Coast, Ghana. 

Y.B. YANKELEVITCH, Dean of the Faculty of Physics and Mathematics, Tomsk Pedagogical Training College, 

Tomsk, USSR. 

367

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