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v

Contents

Acknowledgements viiiIntroduction x

1 Characteristics and classification of living organisms 1Characteristics of living organisms 1Concept and use of a classification system 2Features of organisms 6Dichotomous keys 21

2 Organisation of the organism 23Cell structure and organisation 25Levels of organisation 27Size of specimens 30

3 Movement in and out of cells 33Diffusion 36Osmosis 38Active transport 42

4 Biological molecules 45Biological molecules 47

5 Enzymes 52Enzymes 52

6 Plant nutrition 57Photosynthesis 60Leaf structure 62Mineral requirements 66

7 Human nutrition 70Diet 72Alimentary canal 74Mechanical and physical digestion 77Chemical digestion 80Absorption 82

8 Transport in plants 85Transport in plants 86Water uptake 87Transpiration 90Translocation 92

9781444176469_IGCSE_Biology.indd 5 30/04/14 10:51 PM

vi

9 Transport in animals 95Circulatory system 95Heart 100Blood and lymphatic vessels 101Blood 103

10 Diseases and immunity 105Pathogens and transmission 110Defences against diseases 113

11 Gas exchange in humans 118Gas exchange in humans 118

12 Respiration 130Respiration 132Aerobic respiration 140Anaerobic respiration 146

13 Excretion in humans 151Excretion 153

14 Co-ordination and response 162Nervous system in humans 166Sense organs 170Hormones in humans 173Homeostasis 176Tropic responses 180

15 Drugs 183Drugs 185Medicinal drugs 190Misused drugs 194

16 Reproduction 199Asexual reproduction 202Sexual reproduction 207Sexual reproduction in plants 213Sexual reproduction in humans 216Sex hormones in humans 220Methods of birth control in humans 223Sexually transmitted infections (STIs) 225

17 Inheritance 232Inheritance 240Chromosomes, genes and proteins 243Mitosis 246Meiosis 250Monohybrid inheritance 259


vii

18 Variation and selection 270Variation 275Adaptive features 285Selection 290

19 Organisms and their environment 300Energy flow 304Food chains and food webs 309Nutrient cycles 315Population size 320

20 Biotechnology and genetic engineering 330Biotechnology and genetic engineering 334Biotechnology 338Genetic engineering 342

21 Human influences on ecosystems 351Food supply 353Habitat destruction 359Pollution 344Conservation 350

Index 361


1

1

Characteristics and classifi cation of living organisms

●● Characteristics of living organisms

Key defi nitionsMovement is an action by an organism causing a change of

position or place (see Chapter 14).Respiration describes the chemical reactions in cells that

break down nutrient molecules and release energy (see Chapter 12).

Sensitivity is the ability to detect and respond to changes in the environment (see Chapter 14).

Growth is a permanent increase in size (see Chapter 16).Reproduction is the processes that make more of the

same kind of organism (see Chapter 16). Single-celled organisms and bacteria may simply keep dividing into two. Multicellular plants and animals may reproduce sexually or asexually.

Excretion is the removal from organisms of toxic materials and substances in excess of requirements (see Chapter 13).

Nutrition is the taking in of materials for energy, growth and development (see Chapters 6 and 7).

All living organisms, whether they are single-celled or multicellular, plants or animals, show the characteristics included in the defi nitions above: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

One way of remembering this list of the characteristics of living things is by using the mnemonic MRS GREN. The letters stand for the fi rst letters of the characteristics.

Mnemonics work by helping to make the material you are learning more meaningful. They give a structure which is easier to recall later. This structure may be a word, or a name (such as MRS GREN) or a phrase. For example, ‘Richard of York gave battle in vain’ is a popular way of remembering the colours of the rainbow in the correct sequence.

Key defi nitionsIf you are studying the extended syllabus you need to learn more detailed defi nitions of some of the characteristics of living things.

Movement is an action by an organism or part of an organism causing a change of position or place.

Most single-celled creatures and animals move about as a whole. Fungi and plants may make movements with parts of their bodies (see Chapter 14).

Respiration describes the chemical reactions in cells that break down nutrient molecules and release energy for metabolism. Most organisms need oxygen for this (see Chapter 12).

Sensitivity is the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses (see Chapter 14).

Growth is a permanent increase in size and dry mass by an increase in cell number or cell size or both (see Chapter 16).

Even bacteria and single-celled creatures show an increase in size. Multicellular organisms increase the numbers of cells in their bodies, become more complicated and change their shape as well as increasing in size (see ‘Sexual reproduction in humans’ in Chapter 16).

Excretion is the removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials and substances in excess of requirements (see Chapter 13).

Respiration and other chemical changes in the cells produce waste products such as carbon dioxide. Living organisms expel these substances from their bodies in various ways (see Chapter 13).

Nutrition is the taking in of materials for energy, growth and development. Plants require light, carbon dioxide, water and ions. Animals need organic compounds and ions and usually need water (see Chapters 6 and 7).

Organisms can take in the materials they need as solid food, as animals do, or they can digest them fi rst and then absorb them, like fungi do, or they can build them up for themselves, like plants do. Animals, using ready-made organic molecules as their food source, are called heterotrophs and form the consumer levels of food chains. Photosynthetic plants are called autotrophs and are usually the fi rst organisms in food chains (see Chapters 6 and 19).

1Characteristics of living organismsListing and describing the characteristics of living organisms

Concept and use of a classifi cation systemHow organisms are classifi ed, using common featuresDefi ning speciesUsing the binomial system of naming species

Features of organismsIdentifying the main features of cells

The basic features of plants and animalsThe main features of groups in the animal kingdom

Dichotomous keysUse of keys based on easily identifi able featuresConstruction of dichotomous keys

The fi ve-kingdom classifi cation schemeThe main features of groups in the plant kingdom The main features of viruses


Concept and use of a classification system

5

The use of DNA has revolutionised the process of classification. Eukaryotic organisms contain chromosomes made up of strings of genes. The chemical which forms these genes is called DNA (which is short for deoxyribonucleic acid). The DNA is made up of a sequence of bases, coding for amino acids and, therefore, proteins (see Chapters 4 and 17). Each species has a distinct number of chromosomes and a unique sequence of bases in its DNA, making it identifiable and distinguishable from other species. This helps particularly when different species are very similar morphologically (in appearance) and anatomically (in internal structure).

The process of biological classification called cladistics involves organisms being grouped together according to whether or not they have one or more shared unique characteristics derived from the group’s last common ancestor, which are not present in more distant ancestors. Organisms which share a more recent ancestor (and are, therefore, more closely

related) have DNA base sequences that are more similar than those that share only a distant ancestor.

Human and primate evolution is a good example of how DNA has been used to clarify a process of evolution. Traditional classification of primates (into monkeys, apes and humans) was based on their anatomy, particularly their bones and teeth. This put humans on a separate branch, while grouping the other apes together into one family called Pongidae.

However, genetic evidence using DNA provides a different insight – humans are more closely related to chimpanzees (1.2% difference in the genome – the complete set of genetic material of the organism) and gorillas (1.6% different) than to orang-utans (3.1% different). Also, chimpanzees are closer to humans than to gorillas (see Figure 1.6).

Bonobos and chimps are found in Zaire and were only identified as different species in 1929. The two species share the same percentage difference in the genome from humans.

15

14

13

12

11

10

9

8

7

6

tim

e/m

illio

ns

of

year

s ag

o

5

4

3

2

1

0

Orang-utan48 chromosomes

Gorilla48 chromosomes

Chimpanzee48 chromosomes

common ancestor, now extinct



commonancestor,

now extinct

Bonobo48 chromosomes

Human46 chromosomes

Figure 1.6 Classification of primates, based on DNA evidence


features of organisms

11

The animal kingdomAnimals are multicellular organisms whose cells have no cell walls or chloroplasts. Most animals ingest solid food and digest it internally.

Animal kingdom(Only 8 groups out of 23 are listed here.)

Coelenterates (sea anemones, jellyfish)FlatwormsNematode wormsAnnelids (segmented worms)Arthropods

CLASSCrustacea (crabs, shrimps, water fleas)InsectsArachnids (spiders and mites)Myriapods (centipedes and millipedes)

Molluscs (snails, slugs, mussels, octopuses)Echinoderms (starfish, sea urchins)

VertebratesCLASSFishAmphibia (frogs, toads, newts) Reptiles (lizards, snakes, turtles) BirdsMammals(Only 4 subgroups out of about 26 are listed.)

InsectivoresCarnivoresRodentsPrimates

*

*All the organisms which do not have a vertebral column are often referred to as invertebrates. Invertebrates are not a natural group, but the term is convenient to use.

Arthropods The arthropods include the crustacea, insects, centipedes and spiders (see Figure 1.8 on page 10). The name arthropod means ‘jointed limbs’, and this is a feature common to them all. They also have a hard, firm external skeleton, called a cuticle, which encloses their bodies. Their bodies are segmented and, between the segments, there are flexible joints which permit movement. In most arthropods, the segments are grouped together to form distinct regions, the head, thorax and abdomen. Table 1.1 outlines the key features of the four classes of arthropod.

CrustaceaMarine crustacea are crabs, prawns, lobsters, shrimps and barnacles. Freshwater crustacea are water fleas, Cyclops, the freshwater shrimp (Gammarus) and the water louse (Asellus). Woodlice are land-dwelling crustacea. Some of these crustacea are illustrated in Figure 1.8 on page 10.

Like all arthropods, crustacea have an exoskeleton and jointed legs. They also have two pairs of antennae which are sensitive to touch and to chemicals, and they have compound eyes. Compound eyes are made up of tens or hundreds of separate lenses with light-sensitive cells beneath. They are able to form a crude image and are very sensitive to movement.

Typically, crustacea have a pair of jointed limbs on each segment of the body, but those on the head segments are modified to form antennae or specialised mouth parts for feeding (see Figure 1.12).

second antenna

walking legs

segmentedabdomen

claw

thorax compoundeye

first antenna

Figure 1.12 External features of a crustacean (lobster × 0.2)

InsectsThe insects form a very large class of arthropods. Bees, butterflies, mosquitoes, houseflies, earwigs, greenfly and beetles are just a few of the subgroups in this class.

Insects have segmented bodies with a firm exoskeleton, three pairs of jointed legs, compound eyes and, typically, two pairs of wings. The segments are grouped into distinct head, thorax and abdomen regions (see Figure 1.13).


1 CharaCteristiCs and ClassifiCation of living organisms

12

compound eye 1 pair antennae

abdomen(segmented) 3 pairs of legs

head

wing

thorax

Figure 1.13 External features of an insect (greenbottle, × 5). Flies, midges and mosquitoes have only one pair of wings.

Insects differ from crustacea in having wings, only one pair of antennae and only three pairs of legs. There are no limbs on the abdominal segments.

The insects have very successfully colonised the land. One reason for their success is the relative impermeability of their cuticles, which prevents desiccation even in very hot, dry climates.

ArachnidsThese are the spiders, scorpions, mites and ticks. Their bodies are divided into two regions, the cephalothorax and the abdomen (see Figure 1.14). They have four pairs of limbs on the cephalothorax, two pedipalps and two chelicerae. The pedipalps

are used in reproduction; the chelicerae are used to pierce their prey and paralyse it with a poison secreted by a gland at the base. There are usually several pairs of simple eyes.

chelicera (poison fang)held on undersideof cephalothorax

poison sac

cephalothorax

abdomen

pedipalp

positionofchelicerae

Figure 1.14 External features of an arachnid (× 2.5)

MyriapodsThese are millipedes and centipedes. They have a head and a segmented body which is not obviously divided into thorax and abdomen. There is a pair of legs on each body segment but in the millipede the abdominal segments are fused in pairs and it looks as if it has two pairs of legs per segment (see Figure 1.15).

As the myriapod grows, additional segments are formed. The myriapods have one pair of antennae and simple eyes. Centipedes are carnivorous; millipedes feed on vegetable matter.

thorax (4 segments)

head

simple eye

antenna

up to 70 abdominalsegments fused in pairs

2 pairs of legs on eachpaired abdominal segment

1 pair of legs oneach thoracicsegment

}

Figure 1.15 External features of a myriapod (× 2.5)

Table 1.1 Key features of the four classes of arthropods

Insects Arachnids Crustacea Myriapods

e.g. dragonfly, wasp e.g. spider, mite e.g. crab, woodlouse e.g. centipede, millipede

• threepairsoflegs • fourpairsoflegs • fiveormorepairsoflegs • tenormorepairsoflegs(usually one pair per segment)

• bodydividedintohead,thoraxand abdomen

• bodydividedintocephalothorax and abdomen

• bodydividedintocephalothorax and abdomen

• bodynotobviouslydividedinto thorax and abdomen

• onepairofantennae • twopairsofantennae • onepairofantennae

• onepairofcompoundeyes • severalpairsofsimpleeyes • onepairofcompoundeyes • simpleeyes

• usuallyhavetwopairsofwings

• cheliceraeforbitingandpoisoning prey

• exoskeletonoftencalcifiedtoform a carapace (hard)


Contents

Acknowledgements ixPreface to the reader xi

Chapter 1 The particulate nature of matter 1Solids, liquids and gases 2The kinetic theory of matter 2Changes of state 4Diffusion – evidence for moving particles 6Checklist 8Additional questions 9

Chapter 2 Elements, compounds and experimental techniques 10Elements 10Compounds 13Mixtures 16Separating mixtures 17Accuracy in experimental work in the laboratory 25Gels, sols, foams and emulsions 26Mixtures for strength 28Checklist 29Additional questions 31

Chapter 3 Atomic structure and bonding 33Inside atoms 33The arrangement of electrons in atoms 37Ionic bonding 38Covalent bonding 45Glasses and ceramics 54Metallic bonding 55Checklist 56Additional questions 58

Chapter 4 Stoichiometry – chemical calculations 59Relative atomic mass 59Reacting masses 59Calculating moles 61Calculating formulae 64Moles and chemical equations 66Checklist 69Additional questions 71

9781444176445.indb 5 15/03/14 5:05 PM

Chapter 5 Electricity and chemistry 72Electrolysis of lead(ii) bromide 73Electrolysis of aluminium oxide 74Electrolysis of aqueous solutions 77Electrolysis of concentrated hydrochloric acid 80Electrolysis of copper(ii) sulfate solution 80Electrolysis guidelines 83Electroplating 83Checklist 85Additional questions 86

Chapter 6 Chemical energetics 88Substances from oil 88Fossil fuels 90What is a fuel? 92Alternative sources of energy 93Chemical energy 95Changes of state 97Cells and batteries 98Checklist 100Additional questions 101

Chapter 7 Chemical reactions 104Factors that affect the rate of a reaction 105Enzymes 111Checklist 114Additional questions 115

Chapter 8 Acids, bases and salts 117Acids and alkalis 117Formation of salts 122Crystal hydrates 127Solubility of salts in water 129Titration 129Checklist 132Additional questions 133

Chapter 9 The Periodic Table 135Development of the Periodic Table 135Electronic structure and the Periodic Table 138Group I – the alkali metals 138Group II – the alkaline earth metals 140Group VII – the halogens 141Group 0 – the noble gases 143Transition elements 144The position of hydrogen 146Checklist 146Additional questions 147

9781444176445.indb 6 15/03/14 5:05 PM

Chapter 10 Metals 149Metal reactions 150Decomposition of metal nitrates, carbonates, oxides and hydroxides 152Reactivity of metals and their uses 153Identifying metal ions 155Discovery of metals and their extraction 157Metal waste 161Rusting of iron 161Alloys 165Checklist 168Additional questions 169

Chapter 11 Air and water 171The air 171How do we get the useful gases we need from the air? 174Ammonia – an important nitrogen-containing chemical 176Artificial fertilisers 180Atmospheric pollution 182Water 184The water cycle 186Hardness in water 187Water pollution and treatment 190Checklist 193Additional questions 194

Chapter 12 Sulfur 197Sulfur – the element 197Sulfur dioxide 198Sulfuric acid 199Checklist 203Additional questions 204

Chapter 13 Inorganic carbon chemistry 206Limestone 206Carbonates 211Carbon dioxide 212Checklist 215Additional questions 216

Chapter 14 Organic chemistry 1 218Alkanes 218The chemical behaviour of alkanes 220Alkenes 222The chemical behaviour of alkenes 224A special addition reaction of alkene molecules 226Checklist 230Additional questions 231

9781444176445.indb 7 15/03/14 5:05 PM

Chapter 15 Organic chemistry 2 233Alcohols (R—OH) 233Biotechnology 236Carboxylic acids 237Soaps and detergents 239Condensation polymers 241Some biopolymers 242Pharmaceuticals 246Checklist 247Additional questions 249

Chapter 16 Experimental chemistry 251Objectives for experimental skills and investigations 251Suggestions for practical work and assessment 251Notes on qualitative analysis 261

Revision and exam-style questions 264Alternative to practical paper 264Theory 275

The Periodic Table of the elements 294Index 295

9781444176445.indb 8 15/03/14 5:05 PM

Preface to the readerThis textbook has been written to help you in your study of chemistry to Cambridge IGCSE. The different chapters in this book are split up into short topics. At the end of many of these topics are questions to test whether you have understood what you have read. At the end of each chapter there are larger study questions. Try to answer as many of the questions as you can as you come across them because asking and answering questions is at the heart of your study of chemistry.

Some questions selected from the Cambridge IGCSE examination papers are included at the end of the book. In many cases they are designed to test your ability to apply your chemical knowledge. The questions may provide certain facts and ask you to make an interpretation of them. In such cases, the factual information may not be covered in the text.

To help draw attention to the more important words, scientifi c terms are printed in bold the fi rst time they are used. There are also checklists at the end of each chapter summarising the important points covered.

As you read through the book, you will notice three sorts of shaded area in the text.

Material highlighted in green is for the Cambridge IGCSE Extended curriculum.

Areas highlighted in yellow contain material that is not part of the Cambridge IGCSE syllabus. It is extension work and will not be examined.

Questions are highlighted by a box like this.

You will see from the box at the foot of this page that the book is divided into four different areas of chemistry: Starter, Physical, Inorganic and organic chemistry. We feel, however, that some topics lead naturally on to other topics not in the same area. So you can, of course, read and study the chapters in your own preferred order and the colour coding will help you with this.

The accompanying Revision CD-ROM provides invaluable exam preparation and practice. We want to test your knowledge with interactive multiple choice, mix and match, and true or false questions that cover both the Core and Extended curriculum. These are organised by syllabus topic.Together, the textbook and CD-ROM will provide you with the information you need for the Cambridge IGCSE syllabus. We hope you enjoy using them.

Bryan Earl and Doug Wilford

We use different colours to defi ne different areas of chemistry:

‘starter’ chapters – basic principles physical chemistry inorganic chemistry organic chemistry and the living world.

9781444176445_FM.indd 11 30/04/14 10:49 PM

11 Air And wAter

190

●● water pollution and treatment

An adequate supply of water is essential to the health and well-being of the world’s population. Across the planet, biological and chemical pollutants are affecting the quality of our water. An adequate supply of fresh drinking water is needed for everyone on the planet. Lack of availability of fresh water leads to waterborne diseases, such as cholera and typhoid, and to diarrhoea, which is one of the biggest killers across the world.

Agriculture needs a water supply in order to irrigate crops, especially in areas of the world with hot climates. the production of more and more crops for the ever-increasing population is essential.

water is very good at dissolving substances. thus, it is very unusual to find really pure water on this planet. As water falls through the atmosphere, on to and then through the surface of the earth, it dissolves a tremendous variety of substances. Chemical fertilisers washed off surrounding land will add nitrate ions (nO3

−) and phosphate ions (PO43−) to

the water, owing to the use of artificial fertilisers such as ammonium nitrate and ammonium phosphate.

the nitrates encourage the growth of algae which eventually die and decay, removing oxygen from the water. it may also contain human waste as well as insoluble impurities such as grit and bacteria, and oil and lead ‘dust’ (to a decreasing extent) from the exhaust fumes of lorries and cars (Figure 11.37).

Figure 11.37 A badly polluted river.

All these artificial, as well as natural, impurities must be removed from the water before it can be used. recent regulations in many countries have imposed strict guidelines on the amounts of various substances allowed in drinking water.

Figure 11.38 this lake is used as a source of drinking water.

A lot of drinking water is obtained from lakes and rivers where the pollution levels are low (Figure 11.38). Undesirable materials removed from water include:

●● colloidal clay (clay particles in the water)●● bacteria●● chemicals which cause the water to be coloured and foul tasting

●● acids, which are neutralised.

Making water fit to drinkthe treatment needed to make water fit to drink depends on the source of the water. Some sources, for example mountain streams, may be almost pure and boiling may be enough to kill any micro-organisms present. However, others, such as slow-flowing rivers, may be contaminated. the object of treating contaminated water is to remove all micro-organisms that may cause disease.

the process of water treatment involves both filtration and chlorination and is summarised in Figure 11.39.

1 impure water is passed through screens to filter out floating debris.

2 Aluminium sulfate is added to coagulate small particles of clay so that they form larger clumps, which settle more rapidly.

3 Filtration through coarse sand traps larger, insoluble particles. the sand also contains specially grown microbes which remove some of the bacteria.

4 A sedimentation tank has chemicals known as flocculants, for example aluminium sulfate, added to it to make the smaller particles (which remain in the water as colloidal clay) stick together and sink to the bottom of the tank.

5 these particles are removed by further filtration through fine sand. Sometimes a carbon slurry is used to remove unwanted tastes and odours, and a lime slurry is used to adjust the acidity.

9781444176445_Ch11.indd 190 30/04/14 10:47 PM

water pollution and treatment

191

waterin

screen

pump

1water passed through screen

3coarsesand filter

4sedimentationtank

5fine sandfilter

6chlorine added

pumpsodiumhydroxideadded

coveredstoragetank

tohomesandfactories

2aluminium sulfate added

sulfurdioxideadded

Figure 11.39 the processes involved in water treatment.

6 Finally, a little chlorine gas is added, which sterilises the water and kills any remaining bacteria. excess chlorine can be removed by the addition of sulfur dioxide gas. the addition of chlorine gas makes the water more acidic and so appropriate amounts of sodium hydroxide solution are added. Fluoride is sometimes added to water if there is insufficient occurring naturally, as it helps to prevent tooth decay.

the ‘iron problem’if the acidity level of the treated water is not controlled, problems occur due to the precipitation of iron(iii) hydroxide. these include:

●● vegetables turning brown●● tea having an inky appearance and a bitter taste●● clothes showing rusty stains after washing (Figure 11.40).

Figure 11.40 the rusty stains on this pillowcase are due to iron (iii) compounds in the water.

Sewage treatmentAfter we have used water, it must be treated again before it can be returned to rivers, lakes and seas. this multi-stage process known as sewage treatment is shown in Figure 11.41.

sewage1screens

2settlement tank

3trickling filter

gravel

5sludge(for either dumpingor conversion to fertiliser)and methane gas

4treated water is chlorinatedand returned to the river

Figure 11.41 the processes involved in sewage treatment.

Used water, sewage, contains waste products such as human waste and washing-up debris as well as everything else that we put down a drain or sink. the processes that are involved in its treatment are as follows.

1 Large screens remove large pieces of rubbish.2 Sand and grit are separated in large sedimentation

tanks. the process is speeded up by adding aluminium sulfate, which helps the solids to

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v

Contents

Preface viiPhysics and technology viiiScientific enquiry x

Section 1 General physicsMeasurements and motion 1 Measurements 2 2 Speed, velocity and acceleration 9 3 Graphs of equations 13 4 Falling bodies 17 5 Density 21Forces and momentum 6 Weight and stretching 24 7 Adding forces 27 8 Force and acceleration 30 9 Circular motion 3510 Moments and levers 3911 Centres of mass 4312 Momentum 47Energy, work, power and pressure13 Energy transfer 5014 Kinetic and potential energy 5615 Energy sources 6016 Pressure and liquid pressure 66

Section 2 Thermal physicsSimple kinetic molecular model of matter17 Molecules 7218 The gas laws 76Thermal properties and temperature19 Expansion of solids, liquids and gases 8120 Thermometers 8521 Specific heat capacity 8822 Specific latent heat 91Thermal processes23 Conduction and convection 9724 Radiation 102

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vi

Section 3 Properties of wavesGeneral wave properties25 Mechanical waves 106Light26 Light rays 11327 Reflection of light 11628 Plane mirrors 11929 Refraction of light 12230 Total internal reflection 12631 Lenses 12932 Electromagnetic radiation 135Sound33 Sound waves 140

Section 4 Electricity and magnetismSimple phenomena of magnetism34 Magnetic fields 146Electrical quantities and circuits35 Static electricity 15036 Electric current 15737 Potential difference 16238 Resistance 16739 Capacitors 17440 Electric power 17741 Electronic systems 18542 Digital electronics 193Electromagnetic effects43 Generators 19944 Transformers 20445 Electromagnets 20946 Electric motors 21547 Electric meters 21948 Electrons 222

Section 5 Atomic physics49 Radioactivity 23050 Atomic structure 238Revision questions 245Cambridge IGCSE exam questions 251Mathematics for physics 279Further experimental investigations 282Practical test questions 283Alternative to practical test questions 291

Answers 299Index 307Photo acknowledgements 312

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47

12 Momentum

Momentum is a useful quantity to consider when bodies are involved in collisions and explosions. It is defi ned as the mass of the body multiplied by its velocity and is measured in kilogram metre per second (kg m/s) or newton second (N s).

momentum = mass × velocity

A 2 kg mass moving at 10 m/s has momentum 20 kg m/s, the same as the momentum of a 5 kg mass moving at 4 m/s.

Practical work

Collisions and momentumFigure 12.1 shows an arrangement which can be used to fi nd the velocity of a trolley before and after a collision. If a trolley of length l takes time t to pass through a photogate, its velocity = distance/time = l/t. Two photogates are needed, placed each side of the collision point, to fi nd the velocities before and after the collision. Set them up so that they will record the time taken for the passage of a trolley.

photogate 1 photogate 2

slopingrunway

to timer

trolley with‘interrupt card’

Figure 12.1

A tickertape timer or motion sensor, placed at the top end of the runway, could be used instead of the photogates if preferred.

Attach a strip of Velcro to each trolley so that they ‘stick’ to each other on collision and compensate the runway for friction (see Chapter 17). Place one trolley at rest halfway down the runway and another at the top; give the top trolley a push. It will move forwards with uniform velocity and should hit the second trolley so that they travel on as one. Using the times recorded by the photogate timer, calculate the velocity of the moving trolley before the collision and the common velocity of both trolleys after the collision.

● Conservation of momentum● Explosions● Rockets and jets● Force and momentum

● Sport: impulse and collision time● Practical work: Collisions and momentum

Repeat the experiment with another trolley stacked on top of the one to be pushed so that two are moving before the collision and three after.

Copy and complete the tables of results.

Before collision (m2 at rest)

Mass m1 (no. of trolleys)

Velocity v/m/s

Momentum m1v

1

2

After collision (m1 and m2 together)

Mass m1 + m2 (no. of trolleys)

Velocity v1/m/s

Momentum (m1 + m2)v1

2

3

Do the results suggest any connection between the momentum before the collision and after it in each case?

● Conservation of momentum

When two or more bodies act on one another, as in a collision, the total momentum of the bodies remains constant, provided no external forces act (e.g. friction).

This statement is called the principle of conservation of momentum. Experiments like those in the Practical Work Section show that it is true for all types of collisions.

As an example, suppose a truck of mass 60 kg moving with velocity 3 m/s collides and couples with a stationary truck of mass 30 kg (Figure 12.2a). The two move off together with the same velocity v which we can fi nd as follows (Figure 12.2b).

Total momentum before is

(60 kg × 3 m/s) + (30 kg × 0 m/s) = 180 kg m/s� �

9781444176421_Section_01.indd 47 5/2/14 4:17 PM

12 MOMENTUM

48

Total momentum after is

(60 kg + 30 kg) × v = 90 kg × v

Since momentum is not lost

90 kg × v = 180 kg m/s or v = 2 m/s

3m/sat rest

60 kg 30 kg

v

60 kg 30 kg

a Before b After

Figure 12.2

● ExplosionsMomentum, like velocity, is a vector since it has both magnitude and direction. Vectors cannot be added by ordinary addition unless they act in the same direction. If they act in exactly opposite directions, such as east and west, the smaller subtracts from the greater, or if the same they cancel out.

Momentum is conserved in an explosion such as occurs when a rifl e is fi red. Before fi ring, the total momentum is zero since both rifl e and bullet are at rest. During the fi ring the rifl e and bullet receive equal but opposite amounts of momentum so that the total momentum after fi ring is zero. For example, if a rifl e fi res a bullet of mass 0.01 kg with a velocity of 300 m/s,

forward momentum of bullet = 0.01 kg × 300 m/s= 3 kg m/s

∴ backward momentum of rifl e = 3 kg m/s

If the rifl e has mass m, it recoils (kicks back) with a velocity v such that

mv = 3 kg m/s

Taking m = 6 kg gives v = 3/6 m/s = 0.5 m/s.

● Rockets and jetsIf you release an infl ated balloon with its neck open, it fl ies off in the opposite direction to that of the escaping air. In Figure 12.3 the air has momentum to the left and the balloon moves to the right with equal momentum.

This is the principle of rockets and jet engines. In both, a high-velocity stream of hot gas is produced

by burning fuel and leaves the exhaust with large momentum. The rocket or jet engine itself acquires an equal forward momentum. Space rockets carry their own oxygen supply; jet engines use the surrounding air.

air balloon

Figure 12.3 A defl ating balloon demonstrates the principle of a rocket or a jet engine.

● Force and momentumIf a steady force F acting on a body of mass m increases its velocity from u to v in time t, the acceleration a is given by

a = (v − u)/t (from v = u + at)

Substituting for a in F = ma,

Fm v u

tmv mu

t=−( ) = −

Therefore

force change of momentumtime

= = rat e of change of momentum

This is another version of Newton’s second law. For some problems it is more useful than F = ma.

We also haveFt = mv − mu

where mv is the fi nal momentum, mu the initial momentum and Ft is called the impulse.

● Sport: impulse and collision time

The good cricketer or tennis player ‘follows through’ with the bat or racket when striking the ball (Figure 12.4a). The force applied then acts for a longer time, the impulse is greater and so also is the gain of momentum (and velocity) of the ball.

When we want to stop a moving ball such as a cricket ball, however, its momentum has to be

9781444176421_Section_01.indd 48 5/2/14 4:17 PM

Sport: impulse and collision time

49

reduced to zero. An impulse is then required in the form of an opposing force acting for a certain time. While any number of combinations of force and time will give a particular impulse, the ‘sting’ can be removed from the catch by drawing back the hands as the ball is caught (Figure 12.4b). A smaller average force is then applied for a longer time.

Figure 12.4a Batsman ‘following through’ after hitting the ball

Figure 12.4b Cricketer drawing back the hands to catch the ball

The use of sand gives a softer landing for long-jumpers (Figure 12.5), as a smaller stopping force is applied over a longer time. In a car crash the car’s momentum is reduced to zero in a very short time. If the time of impact can be extended by using crumple zones (see Figure 14.6, p. 58) and extensible seat belts, the average force needed to stop the car is reduced so the injury to passengers should also be less.

Figure 12.5 Sand reduces the athlete’s momentum more gently.

Questions1 What is the momentum in kg m/s of a 10 kg truck travelling at

a 5 m/s,b 20 cm/s,c 36 km/h?

2 A ball X of mass 1 kg travelling at 2 m/s has a head-on collision with an identical ball Y at rest. X stops and Y moves off. What is Y’s velocity?

3 A boy with mass 50 kg running at 5 m/s jumps on to a 20 kg trolley travelling in the same direction at 1.5 m/s. What is their common velocity?

4 A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank, with a horizontal velocity of 3 m/s. With what velocity does the boat begin to move backwards?

5 A truck of mass 500 kg moving at 4 m/s collides with another truck of mass 1500 kg moving in the same direction at 2 m/s. What is their common velocity just after the collision if they move off together?

6 The velocity of a body of mass 10 kg increases from 4 m/s to 8 m/s when a force acts on it for 2 s.a What is the momentum before the force acts?b What is the momentum after the force acts?c What is the momentum gain per second?d What is the value of the force?

7 A rocket of mass 10 000 kg uses 5.0 kg of fuel and oxygen to produce exhaust gases ejected at 5000 m/s. Calculate the increase in its velocity.

Checklist After studying this chapter you should be able to

• defi ne momentum,• describe experiments to demonstrate the principle of

conservation of momentum,• state and use the principle of conservation of momentum

to solve problems,• understand the action of rocket and jet engines,• state the relationship between force and rate of change

of momentum and use it to solve problems,• use the defi nition of impulse to explain how the time of

impact affects the force acting in a collision.

9781444176421_Section_01.indd 49 5/2/14 4:17 PM

ultrasonics

143

tuning fork (sine wave) piano

violin

Figure 33.8 Notes of the same frequency (pitch) but different quality

●l UltrasonicsSound waves with frequencies above 20 kHz are called ultrasonic waves; their frequency is too high to be detected by the human ear but they can be detected electronically and displayed on a CRO.

a) Quartz crystal oscillatorsUltrasonic waves are produced by a quartz crystal which is made to vibrate electrically at the required frequency; they are emitted in a narrow beam in the direction in which the crystal oscillates. An ultrasonic receiver also consists of a quartz crystal but it works in reverse, i.e. when it is set into vibration by ultrasonic waves it generates an electrical signal which is then amplified. The same quartz crystal can act as both a transmitter and a receiver.

b) Ultrasonic echo techniquesUltrasonic waves are partially or totally reflected from surfaces at which the density of the medium changes; this property is exploited in techniques such as the non-destructive testing of materials, sonar and medical ultrasound imaging. A bat emitting ultrasonic waves can judge the distance of an object from the time taken by the reflected wave or ‘echo’ to return.

Ships with sonar can determine the depth of a shoal of fish or the sea bed (Figure 33.9), in the same way; motion sensors (Chapter 2) also work on this principle.

transmitter receiver

ultrasonicwaves

Figure 33.9 A ship using sonar

In medical ultrasound imaging, used in antenatal clinics to monitor the health and sometimes to determine the sex of an unborn baby, an ultrasonic transmitter/receiver is scanned over the mother’s abdomen and a detailed image of the fetus is built up (Figure 33.10). Reflection of the ultrasonic pulses occurs from boundaries of soft tissue, in addition to bone, so images can be obtained of internal organs that cannot be seen by using X-rays. Less detail of bone structure is seen than with X-rays, as the wavelength of ultrasonic waves is larger, typically about 1 mm, but ultrasound has no harmful effects on human tissue.

Figure 33.10 Checking the development of a fetus using ultrasound imaging

▲ ▲

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33 sound Waves

144

●l Seismic wavesEarthquakes produce both longitudinal waves (P-waves) and transverse waves (S-waves) that are known as seismic waves. These travel through the Earth at speeds of up to 13 000 m/s.

When seismic waves pass under buildings, severe structural damage may occur. If the earthquake occurs under the sea, the seismic energy can be transmitted to the water and produce tsunami waves that may travel for very large distances across the ocean. As a tsunami wave approaches shallow coastal waters, it slows down (see Chapter 25) and its amplitude increases, which can lead to massive coastal destruction. This happened in Sri Lanka (see Figure 33.11) and Thailand after the great 2004 Sumatra–Andaman earthquake. The time of arrival of a tsunami wave can be predicted if its speed of travel and the distance from the epicentre of the earthquake are known; it took about 2 hours for tsunami waves to cross the ocean to Sri Lanka from Indonesia. A similar time was needed for the tsunami waves to travel the shorter distance to Thailand. This was because the route was through shallower water and the waves travelled more slowly. If an early-warning system had been in place, many lives could have been saved.

Figure 33.11 This satellite image shows the tsunami that hit the south-western coast of Sri Lanka on 26 December 2004 as it pulled back out to sea, having caused utter devastation in coastal areas.

c) Other usesUltrasound can also be used in ultrasonic drills to cut holes of any shape or size in hard materials such as glass and steel. Jewellery, or more mundane objects such as street lamp covers, can be cleaned by immersion in a tank of solvent which has an ultrasonic vibrator in the base.

Questions1 If 5 seconds elapse between a lightning fl ash and the

clap of thunder, how far away is the storm? (Speed of sound = 330 m/s.)

2 a A girl stands 160 m away from a high wall and claps her hands at a steady rate so that each clap coincides with the echo of the one before. If her clapping rate is 60 per minute, what value does this give for the speed of sound?

b If she moves 40 m closer to the wall she fi nds the clapping rate has to be 80 per minute. What value do these measurements give for the speed of sound?

c If she moves again and fi nds the clapping rate becomes 30 per minute, how far is she from the wall if the speed of sound is the value you found in a?

3 a What properties of sound suggest it is a wave motion?b How does a progressive transverse wave differ from a

longitudinal one? Which type of wave is a sound wave?4 a Draw the waveform of

(i) a loud, low-pitched note, and(ii) a soft, high-pitched note.

b If the speed of sound is 340 m/s what is the wavelength of a note of frequency(i) 340 Hz,(ii) 170 Hz?

ChecklistAfter studying this chapter you should be able to

• recall that sound is produced by vibrations,• describe an experiment to show that sound is not

transmitted through a vacuum,• describe how sound travels in a medium as progressive

longitudinal waves,• recall the limits of audibility (i.e. the range of frequencies)

for the normal human ear,• explain echoes and reverberation,• describe an experiment to measure the speed of sound

in air,• solve problems using the speed of sound, e.g. distance of

thundercloud,

• relate the loudness and pitch of sound waves to amplitude and frequency.

• state the order of magnitude of the speed of sound in air, liquid and solids,

9781444176421_Section_03.indd 144 30/04/14 9:27 PM

251

Cambridge IGCSE exam questions

1 General physicsMeasurements and motion1 a (i) The two diagrams show the dimensions of

a rectangular block being measured using a ruler. They are not shown full size.

Use the scales shown to find the length and the width of the block, giving your answers in cm. [1]

140 150 160 170 180 190millimetres

200 210 220 230 240 250

5060708090100110120130140150160

140210

220230

240250

260270

280290

30025014

010

2030

4050

6070

8090

250

millim

etres

(ii) When the block was made, it was cut from a piece of metal 2.0 cm thick.

Calculate the volume of the block. [2]b Another block has a volume of 20 cm3. The diagram shows the reading when the

block is placed on a balance.

block

40 50grams

60 70

Find the density of this block. [4]

[Total: 8]

(Cambridge IGCSE Physics 0625 Paper 21 Q1 November 2010)

2 An engineering machine has a piston which is going up and down approximately 75 times per minute.

Describe carefully how a stopwatch may be used to find accurately the time for one up-and-down cycle of the piston. [4]

[Total: 4]

(Cambridge IGCSE Physics 0625 Paper 31 Q1 June 2009)

3 Imagine that you live beside a busy road. One of your neighbours thinks that many of the vehicles are travelling faster than the speed limit for the road.

You decide to check this by measuring the speeds of some of the vehicles.a Which two quantities will you need to

measure in order to find the speed of a vehicle, and which instruments would you use to measure them?

Quantity measured Instrument used

[4]

b State the equation you would use to calculate the speed of the vehicle. If you use symbols, state what your symbols mean. [1]

9781444176421_BM_06.indd 251 30/04/14 11:02 PM

eBooksStudent eTextbooksThese time-limited downloadable eTextbooks give your students the freedom to study anytime, anywhere. Assigning eTextbooks to your students enables them to download and view titles on any device or browser.Visit www.hoddereducation.com/igcse to learn more.

Single copyStandard single-copy eBooks are also available through a variety of third party retailers. Email [email protected] for details of your local supplier.

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Teacher’s CD-ROM D. G. Mackean and 9781444196306 December 2014 £65.00 Dave Hayward

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Teacher’s CD-ROM Bryan Earl and 9781444196290 December 2014 £65.00 Doug Wilford

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PHYSICSStudent’s Book 3rd edition Heather Kennett 9781444176421 June 2014 £20.99 plus CD-ROM and Tom Duncan

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Teacher’s CD-ROM Heather Kennett 9781444196283 December 2014 £65.00 and Tom Duncan

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Also Revision Guides coming soon for first examination 2016.

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