p2 student book answers

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© Pearson Education 2011. Edexcel GCSE Additional Science Teacher and Technician Planning GuideThis document may have been altered from the original.

Answers – P2: Physics for your future

P2.1 Static electricity

Student Book

1 Insulating materials2 a Nucleus

b Around the nucleus

3 5, as the positive and negative charges normally balance4 The polythene now has more electrons than protons, so

it has a negative charge. The cloth has more protonsthan electrons, so it has a positive charge.

5 They are on the outside of the atom. Positive chargesare fixed inside the nucleus of the atom and cannotmove.

6 All the strands of her hair have the same charge, so theyare all repelling each other.

7 If the balloons are both made of the same material, theywill both get the same type of charge when they arerubbed on the jumper (this could be positive ornegative). As both balloons have the same charge, theywill repel each other.

8 A good answer will contain the following points:

Rubbing the comb gives it a static charge. If this is a negative charge, it repels electrons in the

pieces of paper, leaving the sides nearest the combwith a positive charge.

The negative charge on the comb and the positivecharge on the pieces of paper attract each other.

(Accept similar answer written assuming a positivecharge on the comb.)

Skills spotlight

A real atom is much smaller than the atom shown. A realatom is three dimensional. Other differences include: therelative sizes of the nucleus and the overall atom – thenucleus is much smaller than the atom; the particles are notcoloured spheres, as drawn here, and they do not have + and

– signs on them!

Activi ty Pack

P2.1b Static electricity questions

1 From top: electron, proton, neutron, nucleus2 Electrons3 Negatively charged electrons have been transferred

from the rod to the cloth.The rod now has fewer electrons than it started with.

4 a Repelb Attractc Repel

P2.1c Static charges

1 Diagram similar to Figure B in Student Book.2 The clothes rub against each other while they are being

tumbled, so electrons may be transferred from one itemto another.

3 a Electrons from the glass rod have been transferred tothe cloth, leaving the glass rod with fewer electrons thanit started with. It now no longer has enough electrons tobalance the positive charges on all its protons, so it hasan overall positive charge.b Attractc If they are made of the same material, they will get thesame charge and so will repel.

4 a Electrons from the jumper have been transferred to theballoon. It now has more electrons than protons, so ithas a negative charge.b The negative charge on the balloon will repel electronsin the near part of the wall. This leaves the near part of

the wall with more protons than electrons, so it has apositive charge. This will attract the negative charge onthe balloon, so the balloon will stick to the wall.

5 a Furniture polish is usually applied by rubbing (or aspray-on polish is then rubbed off with a duster). Therubbing action will transfer electrons between the clothand the surface being rubbed, leaving the surface with astatic charge that will attract dust.b The polish contains a conducting material (such as aspecial polymer) that is left behind as a very thin layer

when the solvent in the polish evaporates. This forms athin conducting layer that prevents a static chargebuilding up.

P2.2 Uses and dangers of static electric ity

Student Book

1 The charge flows through the door to earth.2 a The spark could ignite fuel vapour in the air.

b Any charge built up would be discharged through thebonding line, so there will be no charge to make a spark.c The static charge needs to be discharged before thefuel nozzle gets close enough to the aircraft for a sparkto jump across the gap.

3 a They all have the same charge, and like/similar

charges repel each other.b The object must have the opposite charge to the paintdrops, so that they will be attracted to the object.

4 a The drops of insecticide all have the same charge, sothey spread out to provide a more even coverage.b It means there is less wasted insecticide, so costs ofspraying are cheaper. It might also mean that it isquicker to spray a given area of crops, so again costswill be less.c If it reduces the amount of wasted insecticide, it meansthat the insecticide is only going where it is needed andis less likely to harm other wildlife.


Static electricity can be dangerous if it causes sparks.

This is particularly so in places where the spark might

cause a fire or an explosion. This danger is avoided by making sure that any static

charge is discharged before the spark can occur.

This can be done by earthing the charged object.

Skills spotlight

a Advantage: the spray spreads out more, so the insecticidecan cover the crop more evenly.Disadvantage: the spray may spread out so much that it getsonto crops/hedges that it is not intended for, or it might beeasier for the spread-out spray to be breathed in by people.b Advantage: paint spreads out if it is charged, so it gives amore even coverage, or charged drops of paint are attractedto the object being painted, so less paint is wasted.Disadvantage: a fine mist of paint produced by charging itmight be more flammable/easier to ignite than a paint spray

that is less spread out.

Activi ty Pack

P2.2a Static and helicopters

A – 3d When the helicopter lands its static charge is earthedthrough the tyres, so it is safe to touch.B – 8c The helicopter will have a large static charge. If a personstanding on the ground touches it, that charge will run to earththrough them and give them a severe electric shock.C – 2f The helicopter will have a large static charge. If a personstanding on the ground touches it, or uses an object to touchit, that charge will run to earth through them and give them a

severe electric shock.D – 7



© Pearson Education 2011. Edexcel GCSE Additional Science Teacher and Technician Planning Guide

This document may have been altered from the original.

h The discharge wand allows the charge to run through thewand and the wire to earth, without passing through theperson.E – 6a The helicopter will have a large static charge. If a personstanding on the ground touches the cable, that charge will runto earth through the cable and through them and give them asevere electric shock.F – 4e The discharge wand allows the charge to run through thewand and the wire to earth, without passing through theperson. However, as the helicopter is still hovering, it will

quickly build up another charge unless the wand is kept incontact.G – 1b This is unsafe because the person will be the first thing totouch the ground, so the static charge on the helicopter will bedischarged through them.H – 5g The cable will touch the ground first, so the static chargewill run through the cable, not the person.

P2.2b Using static electricity

1 Your shoes rub on the carpet as you walk.Some electrons are transferred from the carpet to yourbody.You now have a negative charge.When you touch a door handle, the charge can flow intothe door and to earth.You feel a shock when the charge jumps from you to thehandle.You are now discharged.

2 The charged drops spread out so they cover more crops.3 The charged droplets of paint are attracted to the object

being painted.The charged droplets of paint repel each other andspread out.

4 A conducting material that allows electricity to flowthrough it.

5 It earths the aeroplane and the tanker so there are nosparks.

P2.2c Static problems

1 The answer should include: how static charge can buildup, how it can cause sparks when discharged, howsparks could cause a fire if there is fuel vapour around,how a bonding line prevents this by ensuring there is nopotential difference between the tanker and the aircraft.

2 The answer should include how charge can build up ona person, and what happens when a metal object istouched. Advice could include changing shoes for onesmade of a different material that might not build up sucha high charge, or holding a metal object towards thedoor so the spark jumps from the metal and not from theperson's hand.

3 If one of the straps is broken it will not conduct electricityfrom the person to the casing of the board being workedon, so any static built up on the person could suddenly

discharge into one of the components when it istouched.4 If the strap is working properly the lamp will light as there

will be a complete circuit. If one is broken (i.e. notconducting between the wrist strap itself and the clip thatis fastened to the equipment being worked on) then it willnot conduct electricity and so will not discharge theperson using it.

5 Sparks arising from static electricity could damage thecircuitry in such items. If the prongs on a chip are allstuck into carbon-filled foam the conducting nature of thefoam prevents a build-up of static charge that couldharm the component. (Hard drives and new circuitboards are also delivered in anti-static bags.)

P2.3 Electric currents

Student Book

1 A flow of charge – in a metal these moving charges areelectrons.

2 Conducting materials have electrons that are free tomove around between the atoms. Insulating materials donot.

3 a A direct current always flows in the same direction. Inan alternating current, the electrons change directionmany times each second.b Cells and batteries (students may also answer powersupplies)

4 a Coulombsb Amperes

5 3 A × 30 s = 90 C

H6 Time = charge/current = 5000 C / 20 A = 250 s

7 A good answer will contain the following points: Make a circuit using the wire and a cell.

The cell will cause some of the electrons from the metalatoms to move along the wire.

This is a current.

This will not work with an insulating material.

This is because there are no electrons that are free tomove around.

Skills spotlight

The words for different quantities are often different indifferent languages, which could cause problems if scientistsin different countries are communicating with each other.Symbols are quicker to write, and an agreed set of symbolscan be used internationally.

Activi ty PackP2.3a Matching symbols

A, i, voltmeter, measures voltageB, c, resistor, makes the current in the circuit smallerC, f, ammeter, measures currentD, h, open switch, stops current flowing when openE, b, motor, transfers electrical energy into kinetic(movement) energyF, d, lamp or bulb, transfers electrical energy into light andheat energyG, g, cell, pushes electrons around the circuit and gives themenergyH, a, variable resistor, can be adjusted to change the amountof current in a circuit

I, e, wire, conducts electricity around the circuitJ, j, closed switch, allows current to flow in the circuit

P2.3b Currents and calculations

1 A direct current always flows in the same direction. Analternating current changes direction.

2 Charge = current × time = 4 A × 20 s = 80 C3 3.6 A × 60 s = 216 C4 Current = charge/time = 750 C/60 s = 12.5 A5 Time = charge/current = 4000 C/2 A = 2000 s

P2.3c Charges and cur rents

1 a 4.5 A × 20 s = 90 Cb 3.6 A × 60 s = 216 Cc 22 A × 1800 s = 39 600 C

2 800 C/4 A = 200 s

3 a 90 000 C/7200 s = 12.5 Ab 9000 C/18 000 s = 0.5 A

4 a The hosepipe was empty, so she had to wait until thehosepipe had filled up before water started to come outof the end.b The hosepipe still had water in it. When the tap wasturned on, the water going in at that end pushed waterout at Jenny’s end.

5 There are already electrons in the wire. When the switchis pressed the electrons ‘going into’ the wire at that endpush other electrons along. We don’t have to wait for anelectron at the switch to travel all the way to the bulbbefore the light comes on.

6 3 metres = 3000 mm. It would therefore take 3000seconds for an electron to travel from the switch to the

bulb, or 50 minutes.7 a t = Q/I = 1/1.5 × 10-6 A = 6.67 × 105 secondsb t = Q/I = 1/20 × 10-9 = 5 × 107 seconds





P2.4 Current and voltage

Student Book

1 a

b

2 2 A3 a 4 A

b 4 A4

H5 1 V is 1 J per coulomb, so 20 C at 5 V is 20 × 5 = 100 J


Subtract the reading on A2 from the reading on A1 to getthe current flowing through B2.

This works because the current flowing through themain part of the circuit splits up at the junction.

Therefore the sum of the currents through B1 and B2 isthe same as the current in the main part of the circuit.

Skills spotlight

The boiler and pump represent the cell, the pipes representthe wires, the water in the pipes represents the movingelectrons, the heat energy in the water represents the energytransferred by the electrons, and the radiator represents thebulb.

An 'ammeter' in the central heating system would measurethe volume of water passing a point in the circuit eachsecond. A voltmeter would measure the temperature of thewater going into and out of the radiator (or into and out of theboiler).

Activi ty Pack

P2.4b Modelling circuits

1 b The cell pushes the electrons around the wires in thecircuit.

c The electrons do not get used up, they just go roundand round the circuit.d The lamp converts energy from the electrons into lightenergy.e This produces light.

2 B3 C

P2.4c Measuring in circuits

1 a Amperes (or amps), Ab Volts, V

2 a 2 Ab 2 Ac 1.5 Ad 1 Ae 2 A

3 a The current is the same everywhere in a series circuit(or similar explanation).b The current in the branches adds up to the current inthe main part of the circuit (or similar explanation).

4 a Voltmeter drawn across cell, labelled V1b Voltmeter drawn across bulb, labelled V2

5 a In seriesb In parallel

P2.4d Currents and circuits

1 a 2 Ab 2 Ac 1.5 Ad 1 Ae 2 A

2 a Voltmeter drawn across cell, labelled V1b Voltmeter drawn across bulb, labelled V2

3 a The cellb Electronsc The energy carried by the electrons

4 a It increasesb More lorries would leave the supermarket each second

5 a Parallelb Each lorry would have to visit all the supermarkets inturn, unloading only some of the bread at each one.

6 a The number of lorries driving round the route is alwaysthe same; only the amount of bread they are carryingchanges.b The total number of lorries leaving the factory must bethe same number as arrive back, and this total number issplit between the different routes they have to drive(representing different branches of a parallel circuit).

7 a The potential difference represents the energytransferred by each coulomb of charge. If a lorryrepresents the charge, then the potential difference isthe difference in the amount of bread carried by lorriesentering and leaving the factory.b The difference in the amount of bread carried by alorry as it enters and leaves a supermarket (or theamount of bread left at a supermarket).

P2.6 Changing resistances

Student Book

1 It increases2 5 A × 50 Ω = 250 V3 Current and potential difference (or voltage)

H4 R = V/I = 4.5 V / 0.5 A = 9 Ω 5 a LDR

b Thermistorc Variable resistor


The resistance of the thermistor will control the currentflowing through the circuit.

If the temperature rises the resistance of the thermistorwill decrease.

Therefore more current can flow in the circuit.

If the current is higher, the motor driving the fan canturn faster.

Skills spotlight

A is the filament lamp, B is the normal resistor and C is the

diode.The diagrams show complex mathematical relationships butstudents should be able to describe the general shape of thegraph and use this evidence to draw a conclusion aboutwhich component it represents.

Activi ty Pack

P2.6c Components and graphs

C, H, B or J, graph labelled light intensity and resistance.M, G, B or J, graph labelled temperature and resistance.

A, F, L, graph labelled potential difference (x-axis) andcurrent.N, K, D, graph labelled potential difference (x-axis) andcurrent.O, I, E, graph labelled potential difference (x-axis) and

current.P2.6d Components and resistances

1 a Variable resistorb Filament lamp





c Thermistord Diodee Light dependent resistor

2 It will go down/get less.3 10 V / 2 A = 5 Ω 4 a Current = 5 V / 100 Ω = 0.05 A

b It will go down.c It will go up.

5 a Resistance = 12 V / 3 A = 4 Ω b It will go up.c It will go down.

P2.6e Changing resistances

1

Potential difference (V) Current (A) Resistance (Ω)

0 0 -

2 0.38 5.26

4 0.64 6.25

6 0.83 7.23

8 0.98 8.16

10 1.10 9.09

12 1.18 10.17

14 1.24 11.29

2 It goes up.3 a Correctly plotted graph.

b As the potential difference increases the gradient ofthe line gets less. That means for each increase inpotential difference, the increase in current gets less, sothe resistance must be increasing.

4 a 0.26 Ab 0.06 A

5 The resistance must be greater when the potentialdifference is higher, as the 2 V increase in potentialdifference from 12 V to 14 V has resulted in a muchsmaller increase in current than it did from 2 V to 4 V.

6 a

b

7

P2.7 Transferring energy

Student Book

1 Components heat up when electric current flows throughthem, and electronic components do not work properly ifthey get too hot.

2 a Any two useful effects, such as in kettles, electric fires,cookers, electric blankets, tumble dryers, etc. (do notaccept microwave ovens or any other electricalappliance that does not involve direct heating).b Any two examples of wasted heat energy, such asTVs, radios, computers.

3 a 12 V × 3 A = 36 Wb 10 minutes = 600 sEnergy = 12 V × 3 A × 600 s = 21 600 J(or energy = 36 W × 600 s)

H4 Current = power/potential difference = 25 W/230 V = 0.11 A

5 Energy transferred = 358 800 JEnergy = power × timeTime = energy/power = 358 800 J/500 W = 718 seconds(to the nearest second)


Electricity passing through a resistor (such as theelement of a kettle) causes a heating effect.

The power of an electrical appliance can be calculatedusing the potential difference and current.

For the same kettle, a lower potential difference willmean that a lower current flows.

The power will be much less than with a higher potentialdifference.

It takes a certain amount of energy to boil a fixedvolume of water.

The power is the energy transferred per second.

If the power is lower it will take longer for the sameamount of energy to be transferred.

Skills spotlight

Students will need to draw on knowledge from Units C1 andP1 to answer this fully.

Possible advantages include: electric heaters are efficient(very little of the electricity paid for is converted to forms otherthan heat); they do not produce waste gases that can betoxic; they are easier to start than a wood fire; they can beused sustainably if the electricity comes from renewableresources.Possible drawbacks include: their overall efficiency dependson the efficiency of the power station that produced theelectricity, so they may not be as efficient; many people preferthe appearance of flames from a 'real' fire; a wood fire is asustainable means of heating, as long as the wood isharvested sustainably.Possible risks include: risks of electric shocks as well asburns if the heater (and the electricity wiring in the house) isnot installed and maintained correctly.

Activi ty PackP2.7a Choosing the wiring

1 a 500 Wb 500 W/230 V = 2.17 Ac 1.0 mm2

2 a 8500 W/230 V = 36.96 Ab 6.0 mm2 c Because if another high power appliance was used onthe same circuit, the circuit could overload.

3 a 9.6 kW or 9600 Wb 9600 W/230 V = 41.7 Ac 10.0 mm2

P2.7b Electrical heating

1 a Useful

b Usefulc Not usefuld Usefule Not useful

2 Watt3 230 V × 8 A = 1840 W4 Current = power/potential difference = 90 W/230 V =

0.39 A5 Joule6 1840 W × 60 s = 110 400 J (or 230 V × 8 A × 60 s =

110 400 J)

P2.7c Heating and power

H1 a Current = power/p.d. = 90 W/230 V = 0.39 A

b 1000 W/230 V = 4.35 A

c 2000 W/230 V = 8.70 AH2 a Energy = current × potential difference × time

3 hours = 3 × 60 × 60 = 10 800 sEnergy = 0.39 A × 230 V × 10 800 s = 968 760 J





b 5 minutes = 5 × 60 = 300 sEnergy = 4.35 A × 230 V × 300 s = 300 150 Jc 2 minutes = 2 × 60 = 120 secondsEnergy = 8.70 A × 230 V × 120 s = 240 120 J

H3 The electrons collide with the atoms and transfer energy

to them.4 a If it did not, it would melt and break the circuit when the

appliance was working normally.b Many appliances use a smaller current than 13 A, so itis safer to use a fuse that melts only just above thenormal current.

H5 a Current = 0.39 A, fuse = 3 A

b Current = 4.35 A, fuse = 5 Ac Current = 8.70 A, fuse = 13 A

H6 a A higher potential difference causes a higher current to

flow. This means that more electrons are passingthrough the filament each second, and so moreelectrons will collide with the atoms in the filament. Moreenergy will be transferred to heat energy.b They vibrate more.c The vibrating atoms are more likely to get in the way ofthe moving electrons (or similar explanation), so theresistance to the current will increase. The higher thepotential difference, the hotter the filament and the morethe vibrating atoms get in the way of the movingelectrons.

P2.8 Vectors and velocityStudent Book

1 Displacement is the straight-line distance moved in aparticular direction; distance is how far an object hasmoved.

2 The runner has arrived back exactly where they started.3 9 m/s4 Vector quantities such as force and velocity have both a

size and a direction.5 The velocity has changed because the direction is

different.

H6 350 m

7 a 0.8 m/sb 0 m/s

H8 224 m9 A good answer will include the following points:

A distance-time graph shows distance travelled plottedagainst time.

The gradient of a distance-time graph gives the speedbecause speed is distance/time.

A horizontal line shows an object is stationary.

A straight sloping line shows an object with a constantspeed.

The steeper the line, the greater the speed.

Skills spotlight

Suggestions such as: it is easier to see the change in anobject’s motion from a graph, shown as a change in the slopeof the line, than just by comparing values in a table.

Activi ty PackP2.8b Using distance–time graphs

1 4 m/s2 a C

b 10 s3 a B

b 5 m/s4 a D

b The slope is the shallowest so the speed is least.5 8 m/s6 a 55.6 m/s

b 36 minutes (or 0.6 hours or 2160 seconds)7 a 589 m

b 1085 m8 75 s

P2.8c Country w alk

1 1.5 m/s2 2 m/s

3 a 1.4 m/sb No, because the direction is different.

4 At C; 500 m5 a 1000 m

b Displacement is distance in a particular direction asthe crow flies, not the total journey.

6 a 1400 mb 900 sc 1.6 m/s

7 3.5 m/s

P2.8d Lane swimming

1 100 m2 0 m3 0.8 m/s4 a 0.8 m/s up

b 0.8 m/s down; the velocities are opposite as thedirection is opposite.

H5 80 s

H6 3 m

H7 23 m

H8 15 m

9 Length 1, 2 m/s; Length 2, 1.72 m/s; Length 3, 1.72 m/s;Length 4, 2.17 m/s

10 5 m from David’s end of the pool

P2.9 Acceleration

Student Book1 Acceleration is the change in velocity per second. It is

calculated from the equation acceleration = change invelocity/time taken.

2 23.3 m/s2

H3 12 m/s

4 Because velocity is a vector quantity/it has a direction aswell as a size.

5 −5 m/s2

H6 70 s

7 A good answer will include the following points:

Negative acceleration means the acceleration is actingin the opposite direction to the object’s velocity(provided the initial velocity is taken to be positive) so

the object’s velocity in the original direction willdecrease − it will slow down.

If a negative acceleration continues to act, theneventually the object will stop and then start to getfaster in the opposite direction.

Positive acceleration acts in the same direction as theobject’s velocity so the object’s velocity will increase (itwill get faster).

An acceleration of zero will not change the object’svelocity so it will continue at a constant speed.

Skills spotlight

In a car none of the instruments give the speed in m/s andpeople are unlikely to understand speed in m/s. Accelerationfrom 0 to 60 mph uses speed values people understand andgives an idea of how quickly a car can pull away from traffic

lights, or accelerate when overtaking or merging on amotorway.

Activi ty Pack

P2.9a Theme park

Missing values: A, a = 6 m/s2; B, a = -3 m/s2; C, u = 33 m/s,v = 3 m/s, D, u = 25 m/s, v = 5 m/s, E, a = 9 m/s2; F, a = 6 m/s2

P2.9b Acceleration sentences

acceleration : has a direction and so is a vector quantity, hasunits m/s2, is given by the equation (v – u)/t, is given by theequation change in velocity/time takenspeed: does not have a direction and so is not a vectorquantity, has units m/s, is given by the equation distancetravelled/time taken

distance: does not have a direction and so is not a vectorquantity, has units mdisplacement: has a direction and so is a vector quantity,has units m





velocity: has a direction and so is a vector quantity, has unitsm/s (note that velocity is displacement in a given time – thedirection must be given)force: has a direction and so is a vector quantitytime: does not have a direction and so is not a vector quantity

P2.9c Acceleration

1 a 5 m/s2 b 1 m/s2, arrow to the rightc –2 m/s2, arrow to the left d 2.5 m/s2, arrow to the left

2 a 10 m/s2 b 5 m/s2 c 5 m/s2 d –1.5 m/s2 e –5 m/s2

P2.9d Changing velocity

1 a a = 1 m/s2, acceleration to the rightb 2 s, acceleration to the left c v = 5 m/s; velocity to the rightd u = 20 m/s; acceleration and velocity in opposite directions

2 a 5 sb 14 m/s

3 a 20 m/sb A velocity of 15 m/s upwards – in the oppositedirection to the original velocity.c -35 m/s

d -175 m/s2

4 a 1.5 sb 20 mc 11.25 m

P2.10 Velocity-time graphs

Student Book

1 Velocity is constant.2 a C

b Bc D

3 A 0.5 m/s2

B 2 m/s2

C 0 m/s2 D −0.5 m/s2

H4 a A 100 m, B 200 m, C 900 m, D 900 m

b 2100 m5 A good answer will contain the following points:

Suitable graph with time on horizontal axis and speedon the vertical axis.

Values of acceleration for the different parts (10 m/s2,20 m/s2, 7.1 m/s2, −10 m/s2, −6.6 m/s2).

Possible extra information could be: label to showwhere the greatest acceleration was (from 4 to 16 s);label to show where the Thrust started to slow down(peak of graph).

Skills spotlight

Advantages: very easy to compare sizes and sign ofacceleration in number form; numbers are quicker to use forcalculations; would have to find the gradient to put a value onan acceleration from a graph.Disadvantages: not as visual, so not as easy to comparechanges in acceleration over time as on a graph.

Activi ty Pack

P2.10a Shooting script

1 Suitable graph2 15–17 s; steepest slope3 5–15 s and 17−20 s; horizontal lines on graph4 15–17 s and 22–25 s; the line slopes downwards with time5 Accelerations: 6 m/s2, 0 m/s2, –7.5 m/s2, 0 m/s2,

2.5 m/s2, –6.7 m/s2 6 75 m, 300 m, 45 m, 45 m, 35 m, 30 m

P2.10c Veloci ty–time graphs1 a Correct lines drawn

b Speeding up into a gallop; steeper slope2 A, 4 m/s2; B, 0 m/s2; C, 1 m/s2; D, –5 m/s2; E, –1 m/s2

P2.10d Velocit ies and accelerations on graphs

1 A, 4 m/s2; B, 0 m/s2; C, 1 m/s2; D, –5 m/s2 2 102.5 m3 E, 1 m/s2; F, 0.4 m/s2; G, –0.2 m/s2; H, 0 m/s2; I, –3 m/s2;

J, 2 m/s2.4 793.75 m5 a Graph plotted correctly (straight line sloping down from

maximum velocity 30 m/s)b at 3 sc –10 m/s2 d 45 me 90 m

P2.11 Forces

Student Book

1 a Upthrust and weight; or drag and push from diverb Push from diver, because the arrow is larger

2 Simple free-body diagram showing downward forcearrow from bird labelled ‘weight’ and upward force arrowfor reaction labelled ‘reaction from fence post’. The fencepost should not be shown.

3 Force of rocket on hot gases and force of hot gases onrocket

4 53 000 N5 The force on the rocket would be in a different direction

too so it would change its direction of motion.

6 Suitable free-body diagrams – each should only showone object and the forces acting on it.7 A good answer will contain the following points:

Clear diagram showing push of astronaut on diver andpush of diver on astronaut.

The two forces should be shown as arrows in oppositedirections.

The two arrows should be equal in size.

Diagram shows forces on two objects, whereas free-body diagrams just show forces on a single object.

Skills spotlight

A free-body diagram shows just the forces acting on a singleobject, so they are not confused with the forces acting onother objects.

Activi ty PackP2.11a Everyday forces

a, squashing force on balloon; b, weight and upthrust on boat;c, weight and tension force on lamp; d, weight and magneticforce on paperclips; e, lift, weight, thrust and air resistance onaeroplane; f, stretching force on chest expander.

P2.11c Forces and d iagrams

1 Students’ own free-body diagrams with forces correctlylabelled.

2 a Pull of string on the brick/pull of brick on the string; pullof string on the balloon/pull of balloon on the stringb Weight of the balloon, pull of string on the balloonc Upthrust from the aird Forces are weight of balloon, upthrust from the air, pull

of string on the balloon.

P2.11d Moving in space

1 a Diagram labelled with weight of astronaut, upthrustfrom waterb Free-body diagram showing forces from part a.

2 Weight of astronaut, upthrust from water, pull of rope onastronaut, pull of astronaut on rope

3 The action force of the astronaut on the rope is equal and opposite to the reaction force of the rope on theastronaut.

4 a Diagram showing weight of astronaut, upthrust ofwater and pull of rope on the astronautb As part 1b.

5 a The reaction force pushes on the astronaut andpushes her in the opposite direction – away from thespace station.b Sensible suggestions such as using ropes or clips.





P2.12 Resultant forces

Student Book

1 The arrow for thrust is bigger than the arrow for airresistance (drag).

2 Simple free-body diagram with labelled forces lift(upwards), weight (downwards), thrust (to the right) anddrag or air resistance (to the left). Sizes of arrows samerelative size as in Student Book.

3 0 N4 103 N5 a Because the lift is equal to the weight.

b Because the thrust is greater than the air resistance.6 There is no air resistance in space.7 A good answer will contain the following points:

No thrust means that there is no forward force.

There is still drag because the craft is moving.

There is a resultant force in the opposite direction to thecraft’s motion.

This gives a negative acceleration that slows the craftdown in the forward direction.

The lift must be less than the weight.

The resultant force is therefore downwards.

This gives an acceleration downwards, which meansthe craft loses height.

Skills spotlight

Qualitative: The diagram in Figure B uses arrows withdifferent sizes to compare forces.Quantitative: Worked example uses numerical values to showthe resultant force.

Activi ty Pack

P2.12a Why do th ings move?

True: A, F, G, HFalse: B, C, D, E

P2.12b Theories of motion

1 a An object needed a force to be acting to keep it inmotion.b The feather did not have as big a force on it so itmoved more slowly.

2 a A moving object did not need a force to keep it moving.It would carry on at a steady speed unless a force actedto slow it down.b The friction force had more effect on the feather so itmoved more slowly.

3 a Newton’s first lawb Newton also included stationary objects.

4 a By thinking about observations.b By carrying out experiments and by ‘thought’experiments.c Galileo’s method

5 a All objects need a force to keep them moving.b Resistive forces act to slow the bicycle down. Thecyclist must pedal to balance these forces.

6 a Answers may vary. One answer could be no, becausethe packages are moving in a different direction to the

car, so there is no force to keep them moving forward.b Yes. The packages continue to move in the originaldirection. The friction between the packages and thecarpet in the back of the car is not enough to change thedirection of motion immediately.c Third law

P2.12c Forces and motion

1 b Accelerates forwardc Slows down (accelerates backwards)d Changes direction

2 a Rightb 4 N

3 a balanced forces; the car will continue forwards at asteady speed

b 300 N upwards; the helicopter will accelerate upwardsP2.12d Resultant forces

1 a 10 N upwards, the bag is lifted upwardsb 15 N forwards, the ball accelerates forwards

c Friction force backwards, the skateboard slows downd No resultant force, the fish doesn’t move in anydirectione No resultant force, the boy doesn’t move in anydirectionf 16 N in direction the cue hit the pool ball, the ballaccelerates forwardsg 500 N forwards, the car accelerates forwards

2 a 200 Nb Forwardsc It will increase the speed and so will also increase thelift, so the aeroplane will accelerate upwards.

d The reaction force from the air pushes the aeroplaneforwards.

3 a His weight downwards and the upwards push from thefloor of the lift.b The upward force is larger than Thomas’s weight.c The resultant force is upwards as Thomas isaccelerating upwards.

P2.14 Forces and acceleration

Student Book

1 It will accelerate in the direction of the resultant force.2 A cricket ball has more mass than a tennis ball so the

same force will give the tennis ball a greateracceleration.

3 You would need a much larger force for the lorry,because it has much more mass.

4 The larger catapult will fire the rock faster because it canproduce more force, and so more acceleration.

5 4500 N

H6 9 m/s2


Force = mass acceleration

To achieve the fastest speed at the start the cyclistneeds the most acceleration.

A more massive bike will need more force to give thesame acceleration.

A cyclist with more mass needs to produce more forceto give the same acceleration on the same bike.

A cyclist can only produce a certain amount of force.

So the lowest mass of bike/rider combined will give thegreatest acceleration for the same force.

Skills spotlight

F − stands for force, measured in N

m − stands for mass, measured in kg

a − stands for acceleration, measured in m/s2

Activi ty Pack

P2.14a Accelerating vehic les

1 Cars matched as:

Caterham Super Seven 1.4500 kg

0–60 mph in 4.7 s(5.5 m/s2)

2750 N

Renault Clio1000 kg

0–60 mph in 10.2 s(2.5 m/s2)

2500 N

Ford Focus1500 kg

0–60 mph in 9.3 s(3.0 m/s2)

4500 N

Volvo XC2000 kg

0–60 mph in 7.2 s(3.5 m/s2)

7000 N

Range Rover2500 kg

0–60 mph in 12.7 s(2.0 m/s2)

5000 N

?0–60 mph in 6.6 s(4.0 m/s2)

2200 N

2 Mystery car has mass 550 kg.

P2.14b Force, mass and acceleration

1 a 50 Nb 75 N

2 a 160 N

b 160 Nc 80 N

3 a Greaterb Smaller





4 a Resultant force 8 N, to the left, 4 m/s2 b Resultant force 2 N, to the right, 10 m/s2 c Resultant force 3 N, upwards, 0.75 m/s2 d Resultant force 5 N, upwards, 0.5 m/s2 e Resultant force 100 N, to the right, 40 m/s2

f Resultant force 6 N, upwards, 0.6 m/s2

P2.14c Calculating fo rce, mass and acceleration

1 a 60 Nb 75 Nc 180 Nd 180 Ne 90 N

2 a Resultant 8 N, to the left, 4 m/s2 b Resultant force 2 N, to the right, 10 m/s2 c Resultant force 3 N, upwards, 0.75 m/s2 d Resultant force 6 N, to the right, 12 m/s2 e Resultant force 26 N, downwards, 0.5 m/s2 f Resultant force 2 N, downwards, 0.002 m/s2

3

Object Force (N) Mass (kg) Acceleration (m/s2)

sprinter 160 80 2

charging elephant 1000 1000 1

Formula One car 4500 500 9

cyclist 150 100 1.5

bullet 80 0.002 40 000

hockey ball 4 0.13 30

4 a 180 000 m/s2

b 8100 N5 a -0.0072 m/s2

b 2160000 N

P2.15 Terminal velocity

Student Book

1 Mass is amount of matter in an object; weight is thegravitational force on the object, which depends on thegravitational field strength.

2 a 300 kgb 7500 N

3 The hammer and feather had same acceleration, and

there was no air resistance.4 Terminal velocity5 Air resistance increases with speed.6 a 600 N

b Acts towards the Earth (downwards)c 600 Nd Acts upwards


Both crates travel the same distance to reach the ground.

The full crate has greater mass and so greater weight.

The full crate will need a larger air resistance to balanceits greater weight.

The full crate will have a larger terminal velocity.

A larger terminal velocity means the full crate will travelthe same distance as the empty crate in a shorter time.

So the full crate will reach the ground first.

Skills spotlight

Look for suggestions where students time muffin cases overconsecutive distances, say 0−10 cm, 10−20 cm, and so on.They find the velocity for each distance and see how thevelocity changes as the muffin case falls. A constant valuewould show that the falling muffin cases did reach a terminalvelocity.

Activi ty Pack

P2.15a Terminal velocity

1 a i 750 N downwards ii velocity increasesb i 500 N downwards ii velocity increases less quicklyc i 300 N downwards ii velocity increases less quickly

d i 0 N ii constant velocitye i 750 N upwards ii velocity decreases rapidlyf i 0 N ii constant velocity

2 Suitable graph

P2.15d Weight and terminal veloci ty

1 a 700 Nb 1610 N

2 a 15 000 Nb 13 500 Nc 6000 N

3 a B; there is no resultant force as the two forces arebalanced.b C; there is no resistance force.

4 b, f, g5 a In a vacuum, all objects have the same acceleration

(or similar).

c The terminal velocity does depend on the airresistance of the atmosphere. d When an object reaches its terminal velocity theupward force is equal to the downward force. e The force that accelerates an object downwards is itsweight.

P2.15e Safe landing

1 a 259 Nb 12 kg c 8.9 N/kg

2 a 6764 Nb E (rapid deceleration)c C to Dd B to C and D to E

e C to D and E to F. At C the parachute opened, and atE the lander hit the planet’s surface.f E to F; steepest line so greatest acceleration, and sogreatest force.

3 a On Venus the atmosphere is so thick that the terminalvelocity is very low. The atmosphere on Mars is muchless dense, so the air resistance would be much less.This means that the terminal velocity will be muchhigher, even with a parachute. The spacecraft wouldhave to be moving much faster for the resistance forceto equal the weight. Without the thruster, it would crash.b Similar to graph for Venus. Thruster rockets appliednear end of fall, causing a rapid deceleration.c Any sensible suggestion that the thruster acceleratesthe spacecraft upwards and so reduces its velocity justbefore landing.

P2.16 Stopping distances

Student Book

1 In order to leave a safe distance so they do not crashwhen a hazard appears.

2 17 m3 Braking distance plus thinking distance = stopping

distance, so if braking distance is shorter but thinkingdistance is the same then stopping distance will be less.

4 Thinking distance – no change; braking distance –longer

5 Drinking alcohol increases reaction time, thereforeincreasing thinking distance. This increases stoppingdistance, leading to more crashes.

6 A good answer will contain the following points: Thinking distance is increased by:

alcohol; drugs; tiredness; faster speed

Braking distance is increased by:

faster speed; extra weight; worn brakes; lower frictionroad surface, e.g. mud, gravel, wet, ice

Skills spotlight

Faster speed increases both thinking distance and brakingdistance (the latter significantly). Reducing vehicle speedsreduces the number of accidents, making the roads safer.

Also, faster speeds significantly increase kinetic energy, soaccidents at reduced speeds are significantly less dangerous.

Activi ty Pack

P2.16b Stopping distances summary1 True2 False

If a driver is tired, the thinking distance will be increased.3 True





4 FalseIf the road is wet, the thinking distance will be the same.

5 False A car with four passengers will have a longer brakingdistance than a car with one.

6 FalseIn the rain a driver will need a longer braking distance.

7 True8 C Stopping distance = thinking distance + braking

distance 9 Worn brakes provide less braking force, so braking

distance is increased (so stopping distance is

increased).10 Both thinking and braking distance are increased at

greater speeds.

P2.16c Stopping distances graphs

1 18, 32, 51, 73, 1002

3

Speed(m/s)

Conditions Thinkingtime (s)

Thinkingdistance(m)

Brakingdistance(m)

Overallstoppingdistance (m)

5 Drunk 1.8 9 2 11

10 Drunk 1.8 18 8 26

15 Drunk 1.8 27 17 44

20 Drunk 1.8 36 31 67

25 Drunk 1.8 45 48 93

30 Drunk 1.8 54 70 124

4

5

Speed(m/s)

Conditions Thinkingtime (s)

Thinkingdistance(m)

Brakingdistance(m)

Overallstoppingdistance (m)

5 Normal 1 5 2.4 7.410 Normal 1 10 9.6 19.6

15 Normal 1 15 20.4 35.4

20 Normal 1 20 37.2 57.2

25 Normal 1 25 57.6 82.6

30 Normal 1 30 84 114.0

6

7 It is an easy to remember method for making suredrivers have sufficient space to stop safely if the car infront stops suddenly.

8 These make the stopping distance longer.9 If the car in front is moving faster, it will take longer to

stop as well.

P2.18 Momentum

Student Book

1 a 14600 kg m/s northb 20 000 kg m/s south

2 Velocity is zero, so mass × velocity is zero.H3 120 kg

4 a 120 kg m/s and zerob 120 kg m/sc To the rightd 120 kg m/s to the righte Yes

5 A sleeping cat – not moving so zero momentum. A running dog – moving but it is slower and has lessmass than both the others.The meteorite from question 3.

A monster truck in a race – in the worked example themonster truck has more momentum than the meteoriteand is not going at race speed.


Need to know the mass and velocity.

Multiply these to calculate momentum.

Conservation of linear momentum means same totalmomentum before and after a collision.

So it will be conserved in a crash.

So can work out the velocity of vehicles after crashing.

If you know their mass.

Skills spotlight

Video recording of crash allows qualitative by justlooking and describing what happens to each car.

Could use markers painted on road and car to actuallymeasure movements in video, also knowing time foreach video frame.

Could datalog speedometers from cars, plus additionalsensors like accelerometers or forcemeters.

Qualitative advantage – can produce generalconclusion for all crashes (such as head-on crashes aremore dangerous than glancing impacts).

Quantitative advantage – can use results to informdesign specifically (e.g. bumper strength must be aminimum of…).

Activi ty Pack

P2.18b Explaining momentum conservation

1 Gravity speeds it up, so its momentum increases.2 Momentum is conserved, so if the first ball stops, its

momentum is transferred to the far one, which moves offwith the same momentum as the first one had.

3 As answer to 2, but the initial momentum is greater, sofinal momentum must also be greater.

4 As answer to 2, but the initial momentum is greater, sofinal momentum must also be greater.

5 Gravity is an external force so can change momentum. As one ball swings up at the end, it slows and changesdirection, thus changing its momentum.

P2.18c Momentum calculations

1 560 kg m/s 2 220 kg m/s3 33 kg m/s4 144 kg m/s5 55 kg m/s6 07 36 kg m/s8 25 800 kg m/s

9 0.0002 kg m/s10 402 kg m/s

H P2.18d Penguin collisions

1 a 66 kg m/s





b To the rightc Zerod To the righte 6 m/sf Momentum is conserved

2 a 56 kg m/sb -36 kg m/sc They are opposited You must account for its direction.e -28 kg m/sf 8 m/sg Momentum is conserved.

P2.20 Momentum and safety

Student Book

1 This reduces the forces involved. Lower force meanslesser injury.

2 On impact, the air bag squashes, reducing the rate ofchange of momentum and so reducing the force on yourhead. If your head hits the dashboard it will stopsuddenly, reducing the momentum very quickly and socausing your head to connect with great force.

3 On impact, the bubbles squash slowly, reducing the rateof change of momentum, and so reducing the force onthe object being protected.

4 a They both squash to reduce the rate of change ofmomentum, protecting the contents.b The car has designed failure points so it crushes in adesigned way.

H5 a 600 N

b 40 kg m/s/s; 40 N

H6 2.25 s


Crumple zone

Reduces a car’s momentum more slowly.

This means less force.

Air bag

Reduces a passenger’s momentum more slowly.

This means less force.

Seat belt

Reduces a passenger’s momentum more slowly.

This means less force. Less force means lesser injuries.

Skills spotlight

Variables to be measured:Independent: number of layers of bubble wrapDependent: damage suffered by eggControl variables: drop height, egg mass, uniformity ofwrapping, landing surfaceMethod:Choose the height, measure it out, and mark drop position.From a large selection of eggs, measure their masses andselect several of identical mass.Drop an unwrapped egg from the drop position.Record the damage suffered by the egg.Repeat with a layer of bubble wrap wrapped uniformly aroundthe egg.Record damage.Repeat with an egg with 2 layers and record the damage.Continue repeating, each time with one additional, uniformlayer of bubble wrap.Stop when the damage suffered is zero.Repeat entire experiment.If possible, also repeat entire experiment with eggs of adifferent mass.

Activi ty Pack

P2.20b Momentum changes and road safety

1 Ticks: A, C, D, F, GCrosses: B, E, H

2 A3; B4; C8; D1; E7; F6; G2; H5

P2.20c Momentum and car safety

seat beltscrumple zone

air bagsbumpersheadrests

All act in the following way:-large momentum gets smaller via a force that removesmomentum-slower change in momentum needs smaller force-large forces hurt people-so all slow down change in momentum to protect people.

P2.20d Forces change momentum

1 All act in the following way:

large momentum gets smaller via a force that removesmomentum;

slower change in momentum needs smaller force;

large forces hurt people;

so all slow down change in momentum.

In relation to the equation, they increase value of t,whilst mv – mu is the same, so F is reduced.

2 1400 N3 33.3 N4 0.5 N

H5 a 7 kg m/s

b 10 m/s6 1500 N

H7 13 m/s

H8 9.53 s

H9 10 m/s10 New force is 83 333 N (c.f. original of 250 000 N) so

reduction is 67% of original.

P2.21 Work and power

Student Book

1 Amount of energy transferred2 a 2000 joules

b 5000 J3 a 420 J

b 106 400 Jc 4800 J

4 a 210 Wb 266 Wc 600 W

5 At higher speeds a car has more kinetic energy. Thebrakes have to do more work to remove all of this kineticenergy. The maximum braking force is constant, so thetime taken must be greater if the work done is greater.

H6

Initialvelocity(m/s)

Initial kineticenergy (J)

Work doneto stop (J)

Brakingforce (N)

Brakingdistance (m)

5 12 500 12 500 5000 2.5

10 50 000 50 000 5000 10

15 112 500 112 500 5000 22.5

20 200 000 200 000 5000 40


Braking changes kinetic energy into heat. If you brake hard, so that this heat is generated faster

than the brakes can cool, they will get hot.

Heat can damage the brakes.

So if they overheat the brakes may fail.

Braking more suddenly uses more force.

Braking more suddenly generates heat more quickly.

So brakes are less likely to cool quickly enough.

This makes them more likely to overheat and fail.

Skills spotlight

Example answers:If the amount of energy used was an important cost factor,then the appropriate power could be chosen using thequantitative information.

If only certain machines are available, then knowing which aremore or less powerful will allow an appropriate change ofmachine when one is found to be lacking.





Activi ty Pack

P2.21b Warehouse work

1 Students’ own answers. Examples as in the picture (fromtop left):

jerry cans: 240 J each; water tanks: 320 J each; 5.5 kilocartons: 110 J each; wood bundle: 200 J; sand bags:810 J each; oil drum: 1125 J; paving slabs: 350 J each;crate: 382.5 J; paint tins: 60 J each.

2 E.g. oil drum cannot go more than 2.8 m at a time, so wouldneed to go to 2 m shelf first and then up to top shelf.

3 Students’ own answers, combining answers to 1 and 2.

4 E.g. paving slabs from floor to 4 m shelf is 560 J so112 W, so SLOW LIFT.

P2.21c So much work

1 1500 joules2 3300 J3 13 200 J4 600 J5 3000 J6 50 J7 a 5500 J

b 367 W8 a 3740 J

b 1870 W9 a 50 000 joules

b 6250 W

P2.21d Work and power and work to stop cars

1 50 J2 a 5500 J

b 367 W3 a 3740 J

b 1870 W4 a 50 000 J

H b 8 s

5 a

b The relationship is almost linear. The slight variationfrom direct proportionality indicates the slight variation inmaximum braking force in real-life situations.c Work done in joules:

10400

41600

88400

161200

249600

364000

H d Times in seconds:

0.14

0.58

1.23

2.238889

3.47

5.06

6 Kinetic energy is directly proportional to velocity squared.

P2.22 Potential and kinetic energy

Student Book

1 a 20 Jb 96 000 Jc 30 000 J

2 a 4 Jb 2240 Jc 98 000 J

H3 10 m/s

H4 0.2 m

5 The kinetic energy is converted into heat.6 A good answer will contain the following points:

GPE = mass × height × gravitational field strength

So need to know m, g and h

This is transferred into KE as it falls

Because h (and hence GPE) is reducing

KE = ½ × mass × (velocity)2

So need to know m and v

Skills spotlight

Work = force × distance GPE = mass × gravitational field strength × height

Equations allow scientists to make quantitativestatements.

This allows design to be informed by a need to usespecific numerical values.

For example, lifting against gravity is doing work, soF × d = m × g × h

So F = m × g

So a crane would need to be designed to provide aforce equal to the weight of anything it needs to be ableto lift.

Activi ty Pack

P2.22a The car catapul t

1

Rubberbandstretch, d(cm)

Startvelocity ofcar (m/s)

Kineticenergy (J)KE = ½ mv2

Verticaldistance carmoved (m)

GPEgained (J)GPE = mgh

2 1.0 0.2 0.04 0.16

4 1.2 0.288 0.07 0.28

6 1.6 0.512 0.12 0.48

8 2.0 0.8 0.16 0.64

10 2.1 0.882 0.20 0.8

12 2.3 1.058 0.23 0.92

2

3 The greater the kinetic energy at the start, the greaterthe GPE at the end.

4 a Elastic potential energy to kinetic energyb KE to GPE

5 Energy losses such as friction

6 Yes. The fourth result, starting at 8 cm, appears slightlyoff the pattern of the other points.

P2.22b Mars Rovers energy transfers

Rockets – Chemical potential to kinetic and (wasted) heatand sound

Airbag landing – GPE to kinetic (falling) to heat and sound(on impact)Movement up a hill – electrical to kinetic and gravitationalpotential and (wasted) heat and soundSolar panels - light to chemical potential to electricalLaser signalling system – chemical potential to electrical tolightRadioisotope heaters – nuclear potential to heat

P2.22c Sports day energy transfers

1 When this girl falls back down, her GPE will betransformed into kinetic energy.This moving girl has kinetic energy.





Because it is up in the air, the shot has gravitationalpotential energy.To find the GPE of the javelin, we need to know its mass,the gravitational field strength and its height.m = 72 kg, v = 5.5 m/s. What is the KE?KE = ½ × 72 × (5.5)2 = 1089 J.m = 7.2 kg, v = 14.0 m/s. How would you calculate thekinetic energy? KE = ½ × 7.2 × 142 = 705.6 J m = 80 kg, h = 2.2 m, GPE = 1760 J m = 2 kg, v = 3.8 m/s, KE = 14.44 J m = 1.2 kg, h = 11 m, GPE = 132 J

2 The pole vaulter will have 1760 J when hitting the crash

mat as the GPE will all be converted into kinetic energy.P2.22d Sports day energy calculations

1 High jumper, mass, height and gravitational fieldstrength.Girl running on the track, v = 5 m/sShot, h = 3.3 mJavelin, GPE = 78 JBoy on long jump run up, v = 5.5 m/sHammer, m = 7.2 kgDiscus, KE = 72 JPole vaulter, m = 80 kgDog, KE = 14.44 JHat blowing away, m = 0.2 kgHovering bird, GPE = 132 J

2 GPE to KE to heat and sound on impact3 Mass = 80 kg; on impact KE = (starting GPE =) 1760 J

gives v = 6.63 m/s4 The same percentage improvement is a smaller amount,

and there will be a limit on the possible record, so as weget closer to this, improvements become more and moredifficult.

P2.23 Isotopes

Student Book

1 The number of protons in the nucleus2 The total number of protons and neutrons

3 He42

4 a 4 protonsb 5 neutrons

5 a 4, 5 and 4b Beryllium and boron

c Be104 , Be10

5 and Be94

6 F199

7 No, isotopes have the same number of protons butdifferent numbers of neutrons so they actually havedifferent mass numbers.


Isotopes contain the same number of protons butdifferent numbers of neutrons – they have the sameatomic number.

All three isotopes of hydrogen contain one proton.

Hydrogen-1 does not contain any neutrons.

Hydrogen-2 contains one neutron Hydrogen-3 contains two neutrons.

Skills spotlight

Sensible suggestions such as so that these do not depend onthe language spoken by scientists; so that any scientist willunderstand the shortened way.

Activi ty Pack

P2.23a Find the isotopes

2 Cards 1 and 13, cards 2 and 20, cards 3 and 16, cards 4and 19, cards 5 and 17, cards 6 and 23, cards 7 and 18,cards 8 and 21, cards 9 and 14, cards 10 and 22, cards11 and 15

3 Cards 1, 2, 3, 13, 20 and 16; cards 4, 5, 19 and 17;cards 6, 7, 8, 18, 21 and 23; cards 9, 10, 11, 14, 15 and22

4 Beryllium (proton number 4), boron (proton number 5),carbon (proton number 6) and nitrogen (proton number 7)

P2.23b Isotopes

Atom Atomicnumber

Massnumber

Number ofprotons

Number ofneutrons

Number ofelectrons

H11 1 1 1 0 1

H21 1 2 1 1 1

H31 1 3 1 2 1

Li63 3 6 3 3 3

Li73 3 7 3 4 3

C126 6 12 6 6 6

C146 6 14 6 8 6

Mg2412

12 24 12 12 12

Mg2512

12 25 12 13 12

Mg2612

12 26 12 14 12

2 a Atoms with the same number of protons but differentnumbers of neutrons.b Threec Proton number (and number of electrons)

d Mass number and number of neutrons3 Nucleons: The sub-atomic particles in the nucleus of an

atom.Nucleon number: The number of protons and neutrons inthe nucleus of an atom.Proton number: The number of protons in the nucleus ofan atom.

P2.23c Are they isotopes?

1 a

Atom Number ofprotons

Number ofneutrons

Number ofelectrons

A 6 7 6

B 7 6 7

b The mass number is the same.c They have different numbers of protons, neutrons andelectrons.d No, because the proton numbers are different.

2 a

Atom Number ofprotons

Number ofneutrons

Number ofelectrons

C 5 5 5

D 5 6 5

b Same proton number and same number of electrons.c They have different numbers of neutrons and the massnumbers are different.d Yes, they have the same number of protons butdifferent numbers of neutrons, so they are isotopes of

the same element.3 a Be9

4

b P3115

c Ar 4018

d Al2713

e K3919

f Mg2412

4 Atoms that are isotopes and that are electrically neutralalways have the same number of electrons, as theyhave the same number of protons. However, an atomcan lose or gain electrons to become an ion, in whichcase isotopes of the same element could have different

numbers of electrons.





P2.24 Ionising radiation

Student Book

1 An atom with an electrical charge2 –13 44 A few millimetres of aluminium or a smaller thickness of

lead5 To stop gamma rays6

Alpha particle Beta particle Gamma ray

equivalent to thenucleus of a heliumatom – contains 2protons and 2neutrons

electron emittedfrom nucleus

electromagneticwave

charge of +2 charge of –1 not charged

stopped by a fewcm of air or a fewsheets of paper

stopped by a fewmm of aluminium

stopped by a fewcm of lead or manymetres of concrete

most ionising typeof radiation

moderately ionising least ionising formof radiation

7 Its mass number goes down by 4 and its atomic numbergoes down by 2 – it becomes a different element.


Radioactive source emits ionising radiation (e.g. alphaparticles, beta particles or gamma rays).

Ionising radiation collides with oxygen atom.

Collision knocks an electron out of the oxygen atom.

Charge in the nucleus is now not balanced by thecharge on the electrons.

The atom has a net charge and so is an ion.

Skills spotlight

Use the GM tube to measure the activity of a source. Put asheet of paper between the source and GM tube. If the countrate drops to almost zero, it is an alpha source. If not, replacethe paper with an aluminium sheet a few mm thick. If thecount rate drops to almost zero, it is a beta source. If not, it isa gamma source.

Activi ty PackP2.24a Ionising radiation

Alpha particles: largest form of ionising radiation; stopped bypaper; contains two protons; has a charge of +2.

Beta particles: can travel through paper but not a fewmillimetres of aluminium; has a charge of –1

Gamma rays: smallest form of ionising radiation; is not madeof any particles; can travel the furthest distance through air;can travel through a few millimetres of aluminium; anelectromagnetic wave; does not have an electrical charge

P2.24b Types of radiation

1 Beta2 Alpha3 Alpha4 Alpha5 Beta6 Gamma7 Gamma8 Gamma9 Alpha10 Gamma11 Alpha12 Alpha

P2.24c Radiation penetration

1

Radiation Blocked by Penetrating Ionising

alpha skin, paper, a few cm air slightly highly

beta a few mm of aluminium partly partlygamma thick lead highly slightly

2 a Alpha, beta, gamma

b They are not as ionising and so have fewer collisionswith other atoms.

3 Alpha particles4 Unstable; random; decay; ions; loses; gains (last two in

either order)

P2.24d Alpha, beta and gamma radiation

1 a Alphab Alphac Gammad Betae Gammaf Betag Alpha h Gamma

2 If alpha particles cannot reach you then they cannotcause damage to the cells in your body as they would beabsorbed by skin cells on the skin’s surface (or by the airbefore they reached your skin).

3 a A, C and Db B and Ec Beta particles are less ionising and so travel furtherthan alpha particles.d No, because they are emitted in a random process.e The particles in the tracks in the cloud chamber loseelectrons and become ions.

4 Radioactive sources may emit alpha, beta and gammaradiation. Lead will stop all three types of radiation,which is why it is used. (Using aluminium would not beany good because gamma rays can pass throughaluminium and could cause damage to the body.)

5 Jennifer would still be irradiated and contaminated bythe air that she breathed in and the food and drink thatshe ate. It is not possible to be completely protectedfrom radiation as it is present inside your body. Also, youcan never be sure that all gamma radiation from asource has been stopped by the lead.

P2.25 Nuclear reactions

Student Book

1 Neutron2 Two daughter nuclei (barium-141 and krypton-92) and

three neutrons3 Mostly kinetic energy and some thermal energy.4 By other materials absorbing neutrons so that only one

from each fission goes on to cause another fission.5 Because there are many fissions in an uncontrolled

chain reaction.6 a Uncontrolled chain reaction

b No chain reactionc Controlled chain reaction


Two or three neutrons are produced in each fission.

Each of these neutrons can be absorbed by otheruranium-235 nuclei.

The uranium-235 nuclei then become unstable and splitup.

Some of these neutrons need to be absorbed by othermaterials.

Only one neutron should go on to cause another fission.

The reaction will then continue at a steady rate.

Skills spotlight

One neutron: 10 atoms; two neutrons: 1024 atoms; threeneutrons: 59 049 atoms

Activi ty Pack

P2.25b Nuclear fission jigsaw

1 The pieces should make a diagram showing the fission ofuranium-235 and the fission products xenon-143 andstrontium-90.

2 a Proton number 40; mass number 99.

b Correctly labelled diagram similar to Figure B on page256 of the Student Book.





P2.25c Nuclear chain reactions

1 a Neutronb It becomes unstable.c Nuclear fission

2 a Daughter nucleib Neutronsc Energy

3 a Only one of the three neutrons released goes on tocause the fission of another uranium-235 nucleus.b The other neutrons are absorbed by another material.

P2.25d Nuclear reactions

1 a Controlled chain reactionb The other neutrons are absorbed by another material.

2 a The chain reaction becomes uncontrolled.b A nuclear/atomic bombc There is no chain reaction/the reaction will stop.

3 One of the nuclei produced when the uranium-235nucleus splits up.

4 Any sensible suggestions. The proton numbers of thetwo nuclei should add up to 92. The mass numbers ofthe products (including two or three neutrons) shouldadd up to 236.

5 a The reaction will gradually die away until it stopsaltogether.b The reaction will gradually increase – it is uncontrolled.

P2.26 Nuclear powerStudent Book

1 Nuclear energy to thermal energy2 To maintain a steady rate of fission – if this does not

happen, the reactor could explode like a nuclear bomb.3 a To absorb neutrons

b To slow down neutrons4 Don’t store too many of them together and keep them a

reasonable distance apart.5 Flow diagram should include the following stages:

nuclear energy → kinetic energy → thermal energy→ kinetic energy → electrical energy

6 Raise the control rods to increase the rate of the chainreaction.

7 The moderator8 A good answer will contain the following points:

The rate of reaction needs to be maintained at only oneneutron from each fission going on to cause anotherfission.

If the reactor core is cooling down, the rate of reactionneeds to be increased.

Control rods are raised to increase the reaction rate andhence the temperature.

If the reactor is heating up too much, the rate ofreaction needs to be decreased.

Control rods are lowered to reduce the reaction rateand hence the temperature.

Skills spotlight

Sensible suggestions including effect on jobs, site needs to

be outside major population centres, local population mayhave worries about having a nuclear power station nearby,potential hazards in areas that are prone to earthquakes.

Activi ty Pack

P2.26a Control rod feedback loop

1

2 Reactor core: nuclear energy to kinetic energy andthermal energy; kinetic energy to thermal energy.Heat exchanger: thermal energy to kinetic energy.[Turbine: kinetic energy to kinetic energy][Generator: kinetic energy to electrical energy]Some students may also include some of the wastedenergy transfers, e.g. in the generator, kinetic energy isalso transferred to thermal energy and sound energy.

P2.26c Nuclear power station

1 Labels going clockwise from top left: control rod,moderator, turbine, generator, heat exchanger,shielding, nuclear reactor

2 Lines should be drawn connecting the part with what itdoes as follows:nuclear reactor: where nuclear fission takes placeheat exchanger: where water is boiled to make steamturbines: large blades which rotate to drive a generatorgenerator: produces electricity when it spinsshielding: stops radiation and neutrons escaping fromthe reactorcontrol rod: controls the rate of the chain reactionmoderator: slows down neutrons

P2.26d Parts of a nuclear power station

1 A: control rod, B: moderator, C: turbine, D: generator, E:nuclear reactor, F: shielding, G: heat exchanger

2 a To absorb neutrons and slow down the chain reaction.

b Without them, all of the neutrons could go on to causemore nuclear fissions – the reaction would then beuncontrolled and the reactor could explode.

3 a To slow down the neutrons so they can be absorbedmore easily.b The neutrons are travelling very fast when emitted andare not absorbed by the uranium-235 nuclei.

4 The control rods should be raised slightly to increase therate of the chain reaction. This will produce more heatenergy to keep the temperature of the super heatedwater at the correct level.

5 The thermal energy is used to convert water into steam.The steam has kinetic energy, which is used to transferkinetic energy to the turbine. The turbine is connected tothe generator, which transfers kinetic energy to electrical

energy.6 The fission products are radioactive and the shielding

absorbs any radioactivity coming from the reactor.7 No, the pump should be left switched on. It will take a

little while for the chain reaction to stop, so fission is stillhappening and producing thermal energy. The fissionproducts are also producing thermal energy.

P2.27 Fusion – our future?

Student Book

1 Nuclear fusion of hydrogen2 Helium and neutrons

H3 Hydrogen nuclei do not have enough energy to

overcome the electrostatic force of repulsion.

H4 The pressure is much greater in the Sun (so nuclei are

closer together).

H5 Nuclei split up in fission but join together in fusion;

fission can take place at normal temperatures andpressures but fusion needs high temperatures andpressures; fission creates radioactive waste from fuelwhile fusion does not (but in both processes containmentvessels become radioactive).

H6 Other scientists could not get the same results when

they repeated the experiment.7 A good answer will contain the following points:

Very high temperatures and pressures are needed toovercome electrostatic forces of repulsion.

Very difficult to sustain the high temperatures andpressures.

So far none of the experimental reactors have producedmore energy than was put in to heat up the hydrogennuclei and contain them.





Skills spotlight

Sensible suggestions including: Fleischmann and Pons didnot go through the validation process; other scientists werenot able to carry out the experiment and get the same results;they did not produce a paper that was subjected to peerreview.

Activi ty Pack

P2.27d Fission and fusion

1 a False. A uranium-235 nucleus splitting into twodaughter nuclei is an example of nuclear fission.b Truec False. Both nuclear fission and nuclear fusion makethe reactor radioactive.d False. Nuclear fusion is the reaction that is the sourceof energy in stars.e False. Uranium-235 splits up to form two daughternuclei and two or three neutrons are released.f False. In nuclear fusion, smaller nuclei are joinedtogether to form larger ones.g True

2 A good answer would include some or all of thefollowing: fusion involves joining two nuclei, whereasfission involves splitting one nucleus. Fusion involvesconditions that are currently difficult to achieve, whereasfission conditions can be achieved relatively easily.Fusion to generate energy is still experimental, whereas

fission is a major source of the generation of electricity.3 A suitable answer including the words, e.g.

Their claims needed to be validated by writing a paperthat was then peer reviewed before it was published.Other scientists needed to be able to carry out the sameexperiment and get the same results.

H P2.27e Fusion reactions

1 Fusion involves joining two nuclei, whereas fissioninvolves splitting one nucleus. Fusion involves conditionsthat are currently difficult to achieve, whereas fissionconditions can be achieved relatively easily. Fusion togenerate energy is still experimental, whereas fission isa major source of the generation of electricity.

2 The nuclei cannot overcome the electrostatic force of

repulsion.3 A fusion reactor has one reaction that starts withdeuterium and tritium and ends up with helium and aneutron. The Sun has several reactions that start withhydrogen nuclei and finish with helium nuclei andneutrons. The temperature in a fusion reactor is about10 times hotter than the Sun.

4 To overcome the electrostatic force of repulsion.5 a Stage 2

b He32

6 The theory needs to be validated by writing a paper thatis then peer reviewed before it is published. Otherscientists need to be able to carry out the sameexperiment and get the same results.

7 It is very difficult to reproduce the conditions of the Sun.

Also, the rate of the reaction in the Sun is 1000 timeslower than that in a fusion reactor.

P2.28 Changing ideas

Student Book

1 a Radioactivity – the emission of ‘invisible’ rays thatcame from uranium, which penetrated through solidmaterials. He also discovered that these rays exposedphotographic plates.b Some materials emit more (ionising) radiation thanothers.

2 a Ionises atoms in cellsb Causes tissue damage, such as skin burns, anddamages DNA, leading to mutations. Some mutations

can lead to cancer. (And if mutations are formed in agamete-producing cell, the resulting child may have adeformity.)

3 They did not know about the long-term effects.

4 Longer-term effects such as mutations that lead tocancer (and other effects such as sterility and blooddisorders) became more obvious as time went by.


Handle sources with tongs, which increases thedistance between the source and your body, so lessionising radiation reaches your body.

Do not point sources at people, which means lessionising radiation will reach their body.

Keep sources in a lead-lined container, as all but themost penetrating ionising radiation is stopped by a fewmillimetres of lead.

Wear gloves and eye protection to reduce the chancesof getting radioactive materials on your skin.

Skills spotlight

They knew that it could burn the skin and, from Becquerel’searlier work, that it could ionise gases.They did not know that it can also cause ionisation in cellsthat can lead to mutations and cancer.

Activi ty Pack

P2.28a Handling radioacti ve sources

The sets are: boxes 1, 6 and 10; boxes 2, 5 and 12, boxes 3,8 and 11, boxes 4, 7 and 9.

P2.28b Radioactive discoveries timeline

1 The correct order is: 3, 5, 1, 4, 22 The hypotheses are:

1 The activity of a source depends on the mass of thesource.2 Sources give out different types of radiation that canbe stopped by different materials.3 Uranium gives out ‘invisible rays’.4 Different types of radiation are stopped by differentmaterials.5 The ‘invisible rays’ given out by uranium can chargethe particles in the air.

P2.28c Safe use of radioactive sources

1 Incorrect. E.g. you should not touch radioactive sourcesbecause they can burn your skin.

2 Correct

3 Correct4 Incorrect. E.g. the hazards of handling radioactive

sources are increased by pointing them at people.5 Incorrect. E.g. scientists did not realise at first that

cancer and other health problems could be caused byionising radiation.

6 Incorrect. E.g. radioactive sources are kept in lead-linedcontainers because most ionising radiation is stopped bya few millimetres of lead.

7 Incorrect. E.g. mutations are caused by smaller amountsof ionising radiation over a long time.

8 Correct.9 Incorrect. E.g. regulations are now in place to prevent

radioactive materials being added to products, althoughat the beginning of the 20th century radium or thorium

was deliberately added to such items. (Students couldargue that the statement is correct, due to backgroundradiation.)

P2.28d Marie Curie in the laboratory

1 Answers should include:

Keep the radioactive source in a lead-lined container,not just in a drawer.

Handle sources with tongs, not with the hands.

Not lift the source close to the eyes.

Wear gloves and eye protection.

Not carry sources close to the body (as Gustave does).2 For all answers: because radioactive substances emit

ionising radiation that ionises cells and causes tissuedamage, and possibly cancer.

Most ionising radiation is stopped by a few millimetresof lead.

This increases the distance between the source andthe body, so less ionising radiation reaches the body.

As above.





Alpha radiation will be stopped by the material of thegloves or glasses; also prevents small particles of theradioactive substance being transferred to the skin oreyes where they could continue to decay and emitradiation.

The closer the source is to the body, the more damageit can do; there is also the risk of the glass tubebreaking (or the seal leaking) and the contentscontaminating the pocket.

3 Marie Curie has reddened skin on her hands. Althoughshe did not know about the hazards of ionising radiationto living things, she could have used the damage to her

skin as evidence that handling radioactive sources washarmful and so they should not be applied directly to theskin (in cosmetics) or swallowed (in food).

P2.29 Nuclear waste

Student Book

1 Fission products, i.e. used nuclear fuel2 They both remain radioactive for tens of thousands of

years.3 HLW produces large amounts of ionising radiation while

ILW produces a smaller (but still significant) amount.4 Inside thick concrete and steel for temporary storage

and transport, and then sealed in glass.5 Geological stability of site, number of people living near

the site, access for transporting waste to the site.6 a Does not produce carbon dioxide when it is generating

electricity. Does not use up fossil fuels.b Because of the risk of accidents like Chernobyl, whereradioactive material was spread over a large area (andthe subsequent risk to human health of drinking/eating/breathing in contaminated water/food/air).


It needs to be stored safely for many tens of thousandsof years.

It takes many tens of thousands of years for the levelsof radioactivity to decrease to safer levels.

The materials it is stored in have to last all this time.

The building structure also has to last for many tens ofthousands of years.

Any materials that leak have to be contained so they donot get into groundwater etc.

Skills spotlight

Answers could include the following points:Firing into space: once the waste is in space it cannotcontaminate the Earth if it leaks; there is lots of radiation inspace from the Sun, so putting the waste into space is notmaking the solar system any more dangerous than it alreadyis (although this argument ignores the possibility of actuallycolliding with the waste).Dumping at sea: the oceans contain a huge amount of water,so any waste that leaks will be diluted and not likely to causeharm to people (this argument ignores any effects on wildlifein the area of the dumping)Storage underground: any radiation leaking from containers

will not be able to get through rock to harm people; the earthnaturally contains radioactive elements, so putting waste herewill not be making it any more dangerous (this ignores the factthat the waste is likely to be far more concentrated than anynaturally radioactive substances in rocks)

Activi ty Pack

P2.29a Advantages and disadvantages of nuclear power

Advantages: No carbon dioxide is produced by a nuclearpower station when it is generating power; nuclear powerdoes not contribute to global warming; fossil fuels are notused as the source of energy; there are skilled jobs availablein a nuclear power station; the risk of an accident happeningis very low; the amount of fuel needed is much less than for afossil fuel power station; over the last 50 years, scientists

have started to become worried about releasing carbondioxide into the atmosphere.

Disadvantages: The waste products of nuclear reactors areradioactive; high level waste is radioactive for many tens ofthousands of years; the public perception is that nuclearpower is dangerous; if an accident does happen at a nuclearpower station, radioactive materials could be spread over alarge area; nuclear waste needs to be stored in a place that issecure for many tens of thousands of years; a lot of energy isused to make the materials used to build the power station;some low level waste is allowed to be discharged into theenvironment, because the activity is very low; the wastestored must be safe from being damaged in earthquakes andother natural events; exposure to radioactive substances can

cause mutations in cells, which can then cause cancer;mining and transporting nuclear fuel produces carbon dioxideemissions; it is very expensive to clean up old nuclear powerstations.

P2.29c Nuclear power and nuclear waste

1 a Advantageb Disadvantagec Disadvantaged Advantage

2 a Radioactive material could get into the widerenvironment, e.g. the water supply.b The rock absorbs the ionising radiation and thereforeprevents it reaching the surface; also the deeper it is themore likely it is to remain isolated from humans and theenvironment for a very long time (for example isolatedfrom near-surface groundwater).c It must have a low risk of earthquakes/groundmovements that would create routes for air or water totravel from the radioactive waste to the surface.d Barrels in the sea can be corroded by the sea water; itis easier to monitor the waste in this store.

3 Any two suitable answers, e.g. risk of accidents thatwould destroy the reactor and hence cause leaks ofradioactive materials; if there is an accident, radioactivematerial could be spread over a large area, with risks tohealth of workers or people living in the ‘fallout’ area;target for terrorists; mining for uranium also has healthrisks due to toxic waste; radioactive waste is difficult tostore safely.

P2.29d Storing and disposing of nuclear waste

1 The waste is radioactive for many tens of thousands ofyears.

2 a Rock absorbs any radiation coming out of the storeand so prevents any radiation reaching the surface; alsothe deeper it is the more likely it is to remain isolatedfrom humans and the environment for a very long time(for example isolated from near-surface groundwater).b So that the store is not damaged if there is anearthquake, otherwise radioactivity could be released ifground movements create routes for air or water totravel from the radioactive waste to the surface.

3 a Containment – placing in a container or other methodof storage; dispersal – spreading into the environment,dilution in air/water to reduce the concentration.

b The one where liquids and gases are released into theenvironment.c Sensible suggestions, e.g. people think it makes theenvironment more radioactive; it can damage plants andanimals in the environment; we don’t know fully whathappens to the radioactivity when it is released.

4 So that if one method fails or cracks, developing a leak,there is another method of containing the radioactivity.

5 It is much more radioactive and so safer storageprocesses need to be in place if it is to be safe.

6 a Students’ own opinionsb Because of public perceptions about the risks to healthand the environment from potential leaks.

7 Sensible suggestions, e.g. knowledge about the sitecould be lost, entrance could become overgrown, thecontainers may still break down over tens of thousandsof years.





b Percentage of background radiation from buildings andsoil and cosmic rays is higher than the UK average;percentage of background radiation from medical andfood and drink is about the same as the UK average;and percentage of background radiation from radon gasis lower than the UK average.

2 The amount of radon gas that comes out of the groundvaries depending on the rock type in the area.

3 a Food and drink, buildings and soil, cosmic rays andradon gas. Buildings are a natural source because thestone used to make them is naturally radioactive.b Medical

4 a One person may have lots of dental or bone X-raysand/or radiotherapy for cancer, whereas someone elsemay not have any X-rays, etc.b People working in radioactive environments; falloutfrom nuclear accidents or weapons testing.

5 Students’ own opinions, with sensible reasons.

P2.32b Monitoring radon levels

1 Radon can be dangerous. When you breathe in, alphaparticles from radon can be absorbed by the lungs,which can lead to an increased risk of cancer.

2 Radon gas builds up inside a house not outside it (radoncan build up as more seeps in through the floor, butcannot disperse unless there is good ventilation).

3 a Provide a continuous read-out of radioactivity levels;can trigger an alarm if activity from radon gets too high.b Much cheaper; provide a record of the total amount ofactivity from radon over a period of time.

4 a More expensive than devices that are left in the house;don’t necessarily provide a record of the overall amountof activity from radon.b Can’t trigger an alarm if activity from radon gets toohigh; have to be sent back to a laboratory for radiationlevels to be calculated.

P2.32c Background radiation

1 a 11.5%b Animals and plants take them in from theirenvironment (soil, air, water).c One person might have a job that involves moreexposure (e.g. pilot, medical technician) or they may

have had more medical treatments such as X-rays orradiotherapy.

2 Cosmic rays – Sun and other stars; radon gas – uraniumin rocks in the ground; medical – radiotherapy treatmentand X-rays; food – radioactive isotopes in the environment

3 All except cosmic rays4 Levels of radon gas from rocks in the ground vary due to

the different rock types in different places.5 a Cosmic rays, because all of the others come from the

Earth (and there is no atmosphere to act as a shield).b The proportion of background radiation from cosmicrays is higher in space (no shielding by atmosphere), theproportion from ground and buildings, radon gas andmedical is lower, but the proportion from food and drinkis likely to be similar.

P2.32d Sources of background radiation1 Nothing can be said to be ‘completely safe’. Even low

activities/amounts can be potentially harmful to cells.2 They compare the activity with the background radiation

activity. If they are similar, the source is ‘safe’.3 The amount would be classified as safe as it is the

normal average amount that people in the UK areexposed to. Since no harm comes to most people fromthis level of radiation, it would be deemed ‘safe’.

4 Any three from: rocks, buildings, food, medicaltechniques like X-rays, cosmic rays from outer space.

5 a Ionising radiation from outer spaceb No, the value depends on altitude. For example,people travelling on a plane are exposed to more cosmicrays than people at ground level (due to less protection

from the atmosphere).6 Yorkshire, Aberdeen and Cornwall7 Rocks, which contain small amounts of uranium-238 and

thorium-232, for example.

8 Our bodies have an activity of, on average, 5000radioactive decays per second.

9 Houses were much more draughty 100 years ago, so theair in the room changed more often and levels of radongas did not build up as much.

P2.33 Uses of radiation

Student Book

1 Radiation from alpha and beta sources inside the bodywould be stopped by the body so could not be detectedoutside it. Also, alpha particles emitted inside the body

would cause a lot of harm to cells and tissue, whereasgamma rays tend to pass through the flesh without beingabsorbed.

2 The use of ionising radiation to treat diseases like cancerby targeting and killing the cancer cells.

3 a To reduce the risk of infection by microorganismsb Some heat-sensitive instruments (e.g. plastic) cannotbe sterilised using heat.

4 Benefits: kills bacteria in food; food can be stored forlonger before going off; kills pests such as insects thatmay be in the food. Drawbacks: public acceptance;perceived risks (also danger that food may already havedeteriorated before the food was treated, e.g. that toxinsmay already have been produced by microorganisms).

5 The food is exposed to gamma rays6 A good answer will include the following points:

Should not all be absorbed by the body – should havesome penetrating power.

Some tracers should be absorbed by certain parts ofthe body but not by others.

Should have a short half-life, of the order of hours, sothat the body is not exposed to too much radiation.

Should have a low activity level – as above.

The radioactive isotope, or the decay product, shouldnot have toxic side effects unconnected with theionising radiation.

Skills spotlight

Students’ own answers, but should include the following:Benefits: public will know if food has been irradiated or notand can make their own choice.

Disadvantages: people may avoid safer food because theydon’t want to consume irradiated food (they may not be awareof all the facts).Ethical issues: it might be unethical not to irradiate food sinceit makes it safer to eat (ethical responsibility to make foodsafer); alternatively it may be unethical to distribute irradiatedfood because not enough is known about the effects, e.g. onvitamin content, or because the motive behind it is for profit(to increase shelf life), not for health reasons. The ethicaltreatment of the environment might also be considered.

Activi ty Pack

P2.33c Radiotherapy

1 a Lungb Ovaries

c Breast2 a WI; CR; SD; VG (other answers possible)

b QF; SH; DO; NC (other answers possible)c DN; SK; RJ; PH (other answers possible)

3 Large amounts of ionising radiation can damage the skinby burning it.

P2.33d Radioactive wordsearch

1 a Cosmic rayb Radon gasc Irradiated Sterilisatione Radiotherapyf Becquerelg Activityh Count ratei Background

j Half-lifek Mutationl Gamma ray



2

C I L T U F D B N U B P L A T

L N R A D O N G A S E J S C L

A P S A F E H T J T T B D T E

M A X V W Y H D K E A A N I A

I R R A D I A T E R N C C V K

P M U T A T I O N I F K B I Q

R U B K O P F R I L R G G T V

O D A X R C O S M I C R A Y O

L P N P E R D U E S E O M G P

H A L F L I F E X A Q U M P S

Z O C O U N T R A T E N A M P

B E C Q U E R E L I H D R E E

B N A A L P H A Y O S S A F E

E B I L N R U W O N J Z Y A D

X E R A D I O T H E R A P Y L

P2.33e Other uses of gamma rays

1 Because the gamma rays can penetrate up to 15 cm of

solid steel.2 Not very, because most of the truck is showing

grey/white.3 They are absorbing some of the gamma rays.4 If there were discrepancies between what the

documentation says and what you can see on theimage.

5 Black6 No, because the gamma rays from the cobalt-60 source

will penetrate solid steel up to 15 cm thick.7 Yes, because metals will absorb some gamma rays so

the guns would make a dark image.8 GM tube and other sensible suggestions9 Students’ own answers10 a Hidden rooms, e.g. in a pyramid

b Need to be able to get to both sides of the structure asthe source has to be on the opposite side to the camera;object cannot be too big otherwise gamma rays will notget through at all.

P2.34 More uses of radiation

Student Book

1 Alpha particles2 Count detected by monitor decreases, so computer

increases pressure applied to the rollers.3 Alpha particles would be stopped by the paper.4 The half-life is much greater than the life of the product,

so the radioactivity of the americium will remainapproximately the same while the smoke alarm is in use.

5 Use same method as for paper, as described in StudentBook.

6 Flow chart should have three feedback loops showingwhat happens when: the paper is too thin; the paper istoo thick; the paper is the right thickness.

7 A good answer should include the following points:

Long half-life

Gamma emitter so that it can get to the detectorthrough the ground

Low activity level so that it does not damage any livingthings

Not poisonous to organisms

Increases the background count

Skills spotlight

I would need data on the number of people whose lives havebeen saved in a fire because a smoke detector woke them upor warned them and allowed them to get out of the house intime.I would also need information about the risks of smokedetectors. For example, has anyone become ill because ofthe radiation emitted by them. This is not likely to happenwhen the smoke detectors are mounted properly, as alphaparticles do not travel far through air. However there may beinformation about harm caused if they are not disposed ofproperly, or if people take them apart.If more people have been helped by smoke detectors thanhave been harmed by them, then the benefits outweigh therisks.

Activi ty PackP2.34b Choosing radioactive sources

1 Americium-241 because an alpha emitter is needed toproduce the ionisation current and the activity needs tostay approximately the same for the life of the product.

2 Strontium-90 because a beta emitter is needed (to passthrough the thin material) with a long half-life.

3 Technetium-99m because a gamma emitter is needed(to pass through the body) with a short half-life.

P2.34c Choosing the correct radioactive sources

Students’ answers may vary – examples are given here.1 Cobalt-60 because a gamma emitter with a half-life of

more than a few days is needed to detect slow leaks.2 Cobalt-60 because a gamma emitter with a long half-life

is needed.3 Technetium-99m because a gamma emitter is needed

with a short half-life.4 Americium-241 because an alpha emitter is needed and

the activity needs to stay approximately the same for thelife of the product.

5 Strontium-90 because a beta emitter is needed with along half-life.

6 Cobalt-60 because a gamma emitter with a long half-lifeis needed.

7 Cobalt-60 because a gamma emitter with a long half-lifeis needed.

8 Activity of the source, how easy is it to obtain, cost.

p2 student book answers

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