Physics for you (GCSE)

388 Pages·1991·35.582 MB·English

by  Keith Johnson

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KEITH JOHNSON
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National Curricu for GCSE
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Digitized by the Internet Archive
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Stanley Thornes (Publishers) Ltd
© Keith and Ann Johnson 1978, 1980, 1986, 1991
First published in 1980 by Hutchinson Education
Reprinted 1980, 1981, 1982, 1983 (twice), 1984, 1985, 1986
Revised edition 1986, 1987
Reprinted 1988, 1989
Major new edition with revisions published in 1991 by:
Stanley Thornes (Publishers) Ltd
Ellenborough House
Wellington Street
CHELTENHAM
Glos. GL50 1YD
England.
Reprinted 1992, 1993 (twice). 1994
British Library Cataloguing inP ublication Data
Johnson, Keith
Physics for you.
I. Title
530
ISBN 0-7487-0565-1
Typeset by Oxprint Ltd OX2 6TR
Printed and bound in Hong Kong
‘What is the use of a book,’ thought Alice, ‘without pictures or
conversations?’
Lewis Carroll, Alice in Wonderland
Everything should be made as simple as possible, but not simpler.
Albert Einstein
There is no higher or lower knowledge, but one only, flowing out of
experimentation.
Leonardo da Vinci
I do not know what I may appear to the world, but to myself
I seem to have been only a boy playing on the seashore, and
diverting myself in now and then finding a smoother pebble or
a prettier shell than ordinary, while the great ocean of truth
lay all undiscovered before me.
Sir Isaac Newton
Introduction
Physics For You is designed to introduce you At the back of the book there is advice for you
to the basic ideas of Physics, and show you how on practical work, the nature of science, careers,
these ideas can help to explain the world in which revision and examination techniques, as well as
we live. some help with mathematics.
This book is based on successful earlier editions Questions at the end of a chapter range from
of the same name, but new pages and extra simple fill-in-a-missing-word sentences (useful for
questions have been added to cover the writing notes in your notebook) to more difficult
requirements of the GCSE Examination and the questions that will need some more thought. In
National Curriculum. calculations, simple numbers have been used to
keep the arithmetic as straightforward as possible.
Physics For You has been designed to be
interesting and helpful to you, whether you are At the end of each main topic you will find a
using it for a pure Physics course or as part of an section of further questions taken from actual
Integrated or Coordinated Science course. GCSE examination papers.
The book is carefully laid out so that each new Throughout the book, cartoons and rhymes are
idea is introduced and developed on a single page used to explain ideas and ask questions for you to
or on two facing pages. Words have been kept to answer. In many of the cartoons, Professor Messer
a minimum and as straightforward as possible. makes a mistake because he does not understand
Pages with ared band in the top corner are the Physics very well. Professor Messer does not think
more difficult pages and may be left out at first. very clearly, but I expect you will be able to see his
mistakes and explain where he has gone wrong.
Throughout the book there are many simple
experiments for you to do. Plenty of guidance is Here I would like to thank my wife, Ann, for her
given on the results of these experiments, in case constant encouragement and help with the many
you find the work difficult. diagrams and cartoons.
Each important fact or new formula is printed in I hope you will find Physics interesting as well as
heavy type or is in a box. There is a summary of useful. Above all, | hope you will enjoy Physics
important facts at the end of each chapter. For You.
Keith Johnson
Professor Messer gets in messes,
Things go wrong when he makes guesses.
As you will see, he’s not too bright,
It's up to you to put him night.
Contents
The small... Basic ideas
1 Units 6
2 Energy 8
3 Molecules 14
Heat (thermal energy)
Expansion 21
Thermometers 30
The Gas Laws 35
Measuring Heat 41
CTSNC Aon duction, Convection, Radiation 46
Seven atoms in a uranyl microcrystal, photographed Physics at work: Heat radiation 56
with an electron microscope and false colour added, Physics at work: Keeping warm 57
They are magnified 100 million times. Changing State 59
Heat Engines 68
Further questions on heat 74
... and the large. Mechanics
Pushes and Pulls 81
Density 88
Pressure 91
More about Forces 98
Physics at work: Bridges 104
Turning Forces 106
Work, Energy and Power 113
Machines 124
Mechanics crossword 131
Velocity and Acceleration 132
Physics at work: Sport 144
Momentum 146
Further questions on mechanics 150
The Andromeda galaxy. It contains about
100 000 million stars, and the distance across The Earth in Space 156
it is over 100 000 light-years (107! metres).
Waves: Light and Sound Nuclear Physics
21 Waves 166 39 Radioactivity 340
22 Light 172 Further questions on radioactivity 354
23 Reflection 178
24 Curved Mirrors 183
25 Refraction 186 Extra sections
Physics at work: Fibre optics 194
Physics at work: Lasers 195 The Nature of Science 356
26 Lenses 196 Famous Names 358
27 Optical Instruments 200 History of Inventions 360
28 Colour 210
29 Sound 220 Doing Your Practical Work 362
Physics at work: Ultrasonic echoes 232
Physics at work: Revision Techniques 366
Electromagnetic waves 233 Revision Programme _ 368
Further questions on waves 234 Revision Checklist 369
Examination Technique 370
Electricity and Magnetism
Careers using Physics 372
30 Static Electricity 239
Check your Maths 374
Physics at work: Static Electricity 244
31 Circuits 246
Answers 376
32 Heating Effect of acurrent 262
33 Chemical Effect of a current 269
Index 380
Further questions on Electricity (1) 272
34 Magnetism 276
Physics at work: Magnets 282
35 Magnetic Effect of a current 284
36 Electromagnetic Induction 296
Physics at work: In yourhome 306
37 Electron beams 308
38 Electronics 314
Physics at work: Communications 332
Physics at work: Satellites 333
Further questions on Electricity (2) 334
> Length
Length is measured in a unit called the metre (often
shortened to m).
A door knob is usually about 1 metre from the
ground; doorways are about 2 m high.
For shorter distances we often use centimetres
(100 cm = 1 metre) or millimetres (LOOO mm =
1 metre).
Experiment 1.1
a) Look at a metre rule. Which marks are centi-
metres and which are millimetres?
b) It is useful to know the length of your hand-
span. Mine is 22 cm (0.22 m); what is yours?
c) Use the metre rule to measure
— the length of your foot
— the length of a long stride
— your height.
In each case write down the answer in
millimetres and also in metres.
When measuring in Physics we try to do it as
accurately as we can.
Professor Messer is trying to measure the length
of a block of wood with a metre rule but he has
made at least six mistakes.
How many mistakes can you find?
Experiment 1.2
Measure the length of a block of wood taking care
not to make any of the Professor’s mistakes.
> Mass
If you buy a bag of sugar in a shop, you will find In Maths and in Physics, a ‘k’
the mass of sugar marked on the bag. It is written Means a thousand of whatever you say
in grams (Q) or in kilograms (kg). ‘Kilo’ always For grams and for metres
means a thousand, so 1 kilogram = 1000 grams. And even, for teachers,
The size of their annual pay.
The mass of this book is about 1 kilogram.
People often get confused between mass and weight
but they are not the same (see pages 81 and 84). ?
Experiment 1.3 ‘kilo’ is not the only prefix:
Lift some masses labelled 1 kg, 2kg, 5kgand 1g.
Mega (M) = 1 million = 1000 000
kilo (k) =1thousand = 1 000
> Time
centi(c) = 1hundredth
In Physics, time is always measured in seconds
(sometimes shortened to s). eS
milli(m) = 1 thousandth =
You can count seconds very roughly, without a 1000
watch, by saying at a steady rate: ONE (thousand) Hermon eres eee ein ia
TWO (thousand) THREE (thousand) FOUR. .. omen 1 000 000
SEUSS) is LNCS HINES "Ser rirv1a teyiee
Experiment 1.4
Use a stopclock or stopwatch to measure the
time for a complete swing of a pendulum or the
beating of your heart.
What is the time for 100 of your heartbeats?
What is the time for one heartbeat? Approximate | Events
By how much does it change if you run upstairs? length of time
in seconds
All the other units you will meet in this book are 101° Expected lifetime of the Sun
based on the metre, the kilogram and the second. 104 Age of the Earth
They are called SI units. 10 Time since the dinosaurs lived
10°" Time since the earliest human
Very large and small numbers 10.8 Time since Isaac Newton lived
10° Average human life span
For very large or very small numbers, we some- 10’ A school term
times use a shorthand way of writing them, by 10° One day
counting the number of zeros (see also page 375). 10° One second
ie 1032 Time for sound to cross a room
For example: 1037 Time for an electron to travel
a) 1 million = 1 000 000 (6 zeros) = 10° down a TV tube
1Ge. Time for light to cross a room
b) 0.000 001 = aqaq (1 millionth) = 10°° 10m Time for light to pass through
spectacles
In this shorthand way, write down: 10-22 Time for some events inside
one thousand, one thousandth, 10 million, one nee
hundredth.
| wish | could find some use for all that energy!
Energy can exist in different forms, as you can see in the cartoon.
People get their energy from the chemical energy in their food.
Cars run on the chemical energy in petrol. A firework in the cartoon
has chemical energy which it converts into thermal energy (heat)
and light and sound energy when it explodes.
Chemical energy is one kind of stored energy or potential energy.
Another kind of potential eneray is the strain energy stored in the
stretched elastic of the catapult.
The bucket over the door also has some stored potential eneray,
called gravitational energy. When the bucket falls down, this
gravitational energy is converted into movement energy.
The moving pellets from the catapult and the moving people all have
movement energy, called kinetic energy.
The television set is taking in electrical energy and converting it to
thermal energy and light and sound energy.
Another form of energy is nuclear energy, which is used in nuclear
power stations.
These forms of energy are shown in the diagram on the opposite
page (see also page 114).