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ANSWERS4 a The momentum of an object is the product of themass of the object and its velocity. Velocity is speedin a particular direction and is, therefore, a vectorquantity. This means that momentum also has bothsize and a specific direction and is therefore also avector quantity. (3)b Both gliders are at rest so the initial momentum iszero. (1)upward force from air flowc i(4)magnetic forceof repulsiontension in threadconnecting A to Bweight of gliderNewton’s third law states that for every actionthere is an equal and opposite reaction. Thismeans that glider A experiences an unbalancedmagnetic force to the left from B and glider Bexperiences an unbalanced magnetic force to theright from A and that each of these forces is thesame size. (3)iii Each glider experiences an unbalanced forcewhich causes them to accelerate away from eachother. (1)d i speed distance travelled time taken, speed 5cm 1.25 stherefore speed is 4 cm/s (2)ii The momentum of A to the left 500 g 4 m/sThis is equal to the momentum of glider B to theright since the total momentum of the glidersremains zeroThe momentum of B to the right 800 g v m/s so800 g v m/s 500 g 4 m/sTherefore v 2.5 cm/s (5)e If the magnets are closer together, the repelling forcebetween them will be greater so the accelerationof each glider after the thread is cut will be greatercausing the gliders to move apart more quickly.However, glider A, with a smaller mass than B, willmove faster as shown in the above calculation. (3)iiUNIT 2 ANSWERSCHAPTER 61 a 3Wb 50 Vc 0.26 Ad 100 W 18 000 s 1 800 000 J (1800 kJ)2 a The kettle is designed for a voltage of 230 V. At thisvoltage, 1.5 kJ of electrical energy is transferred intoheat energy each second.P 1500 Wb I         6.52 A. The fuse should be rated atV230 Varound 7 A or above. The next common rating abovethis is 13 A, so a 13 A fuse is needed.c Electrical energy is being transferred at the rate of100 J/s in the 100 W bulb but only at 60 J/s for the60 W bulb.3 a It can be reset. It does not need to be replaced.b So no electrical energy can enter the appliance. If theswitch was in the neutral wire, electricity could enterthe appliance and could possibly cause a shock if theappliance was faulty.c The outer casing is made from an insulator, e.g. plastic.4 The power ratings of most appliances are shown on theappliance itself.CHAPTER 71 a Electronsb There is a large number of free charge carriers (freeelectrons) in metals, but very few in a plastic.c i 3Cii 1800 Ciii 10 800 CCharges can travel all the way around a completecircuit. An incomplete circuit has gaps, so chargescannot travel all the way around.ii In a series circuit there is only one path for thecurrent to follow. In a parallel circuit there is morethan one path for the current to follow.b S1 Bulbs A, B and C will go out.S2 Bulbs A, B and C will go out.S3 Bulbs D, E, F, G and H will go out.S4 Bulbs D and E will go out.S5 Bulbs F, G and H will go out.S6 Bulbs G and H will go out.c All the bulbs will glow with equal brightness.d It is a series circuit; therefore the current through allbulbs is the same.2 a i3 a iiiVb As each coulomb of charge passes through the 1.5 Vcell, it receives 1.5 J of electrical energy.4 a In the positions shown, the bulb will glow. If S1 ismoved to B, the circuit is incomplete and the bulb willbe turned off. If S2 is then moved to D, the circuit isagain complete and the bulb will glow.b Turning lighting on and off from top and bottom of astaircase.5 In parallel. If the lights are wired in series, the currentthrough the string of lights will be too small to makethem glow, and any faulty bulbs will result in all the bulbsgoing off.6 If connected in series, turning one part of the cooker onwould turn on all the other parts as well.CHAPTER 81 a The current that flows through a conductor is directlyproportional to the potential difference (or voltage) acrossits ends, provided its temperature remains constant.301

302 ANSWERSb2 a 4ΩSAb 0.24 Ac 30 V3 a i Decrease, with increase of temperature.ii Decrease, with an increase in the intensity of light.iiiresistancepiece of wireVc Close the switch and take readings on ammeter andvoltmeter. Alter the variable resistor and take newreadings. Repeat this at least six times. A graph of Iagainst V will show a straight line passing through theorigin, confirming Ohm’s law.d itemperatureA straight line graph passing through the origin,indicating a constant resistance.resistanceIresistancedecreasing withlight intensityVlight intensityiiAs the current increases, the filament gets hotterand its resistance increases.Ib Thermistors can be used in temperature circuits suchas fire alarms and thermostats. LDRs can be usedin light-sensitive circuits such as automatic lightingcontrols.CHAPTER 91 a i 1ii –1iii no chargeb Protons and neutrons are in the nucleus of an atom.Electrons orbit the nucleus of an atom.Viii The resistance in one direction is very high, i.e.the diode will not conduct. The resistance in theopposite direction is much smaller, i.e. the diodewill conduct.Ic The same number.d An ion.e Your diagrams should show that the rubbing transferselectrons from one object to the other. The objectthat gains electrons becomes negatively charged.The object that loses electrons becomes positivelycharged.2 a Static electricity, i.e. excess charge escaping from theshirt/blouse causes tiny sparks which make a noise.b Static electricity is escaping through you and the doorhandle to earth.c The comb has become charged with static electricitywhilst being used. It induces charge on the paper, andthe two attract.0.6V3 a The toner will stick only to those parts of the drum thatare charged.b As they pass through the negatively charged mesh,the dust particles become negatively charged. Higherup the chimney, these charged particles induce theopposite charge on the earthed metal plates, and soare attracted to them.

ANSWERS4 a iiib iiiClouds possibly become charged as tiny iceparticles are moved up and down within them.There are other possible explanations.The conductor is a metal strip, usually from alightning rod on the roof, and running down theoutside of the building. This provides a lowresistance path to earth, so current caused bythe lightning flows down the conductor insteadof through the building (which would damage thebuilding).Unsafe – any two from: near isolated trees/pylons,in swimming pools, on high ground, on top ofbuildings.Safe – inside a building or inside a car.5 Workers connect themselves to the casing of theappliance on which they are working, using a wrist loopand wire. This allows any difference in charge betweenthe worker and the computer to travel along the wiresafely, rather than causing a sudden spark.END OF UNIT 2 QUESTIONS1 a Bb Dc Ad B (4)2 electrons, coulomb,energy resistance, lower (5)3 a Y is an ammeter, (1)Z is a voltmeter (1)b variable resistor (1)c It can be used to change the current. (1)d 2.5 A (1)e 4.0 V (1)f R 4.0 V/2.0 A (1) 2.0 Ω (1)g It increases. (1)4 a I V/R (1) 12 V/10 Ω 1.2 A (1)b Q I t (1) 1.2 A 5 s 6 C (1)negative charge (1) and the material losing electronshas a positive charge (1).b iiic Electrostatic painting attracts paint to the object beingpainted (1) so less paint is wasted (1) and thereforeless paint can be used (1).d An inkjet printer uses the fact that opposite chargesattract (1) and similar charges repel (1) to direct dropsof ink to the correct places on the paper (1).7 a Any four uses, such as cooking, heating water forwashing, heating the house, drying hair, etc. (1)b A fault in an appliance could lead to a live wiretouching the casing (   12 ), and the presence of an earthwire conducts the current to earth and blows thefuse (   12 ). This prevents someone touching the casinggetting a shock (   12 ). A double-insulated hairdryer hasan insulating case, so the person cannot get a shockeven if the fuse has not blown (   12 ).8 a 10V (2)b 13 A (1)c A double-insulated appliance has an outer casingmade of plastic or other insulating material. (1)So even if there is a fault inside, making a live wiretouch the casing, the user will not get a shock. (1)d R V/I 230V / 8.7A 26.4Ω (1)6 a Two insulating materials are rubbed together (1),which transfers some electrons from one material tothe other (1). The material that gains electrons has ab 2V (2)c 12V (1)UNIT 3 ANSWERSCHAPTER 101 a The vibrations of a transverse wave are across thedirection in which the wave is moving. The vibrationsof a longitudinal wave are along the direction in whichthe wave is moving.b Transverse waves: light (or any other electromagneticwave) or surface water waves.Longitudinal waves: sound waves.cwavelengthc E V I t (1) 12 V 1.2 A 60 s 864 J (1)P5 a I     (1)V2300 W (1) 230 V 8.7 A (1)Any static charge that has built up on the aircraftin flight (1) can be discharged through the earthingwire (1) instead of causing a spark which couldignite fuel vapour (1).A wire is attached from the aircraft to a point onthe tanker. (1)amplitude2 a 0.4 s3 ab4 abcb 2.5 Hz1500m/svƒ     1000 Hz1.5 m1T     0.001 sƒThe wavefronts are squashed closer together as thecar approaches.It would be higher.It would be lower than when the car is stationary.5 Rays of light from the fish have been refracted at thesurface of the water so the hunter does not see thecorrect position of the fish.303

304 ANSWERSCHAPTER 112 a and b1 a They all transfer energy, are transverse waves, travel atthe same speed through a vacuum, can be reflected,refracted and diffracted.b Light, microwaves and radio wavesc Microwaves and infra-red wavesd Gamma rayse Infra-redf Microwaves2 a Water molecules within the food absorb themicrowaves and become hot, so the food cooksthroughout, not just from the outside as in the case ofa normal oven.b X-rays pass easily through soft body tissue butcannot travel through bones. Therefore bones leave‘shadows’ on X-ray photographs, which show theshape of the bone and therefore can show if boneshave been broken.c The Earth’s ozone layer absorbs large quantities ofthe Sun’s UV radiation. If this layer is damaged, moreUV light will reach the surface of the Earth. UV light isharmful to human eyes and can cause skin cancer.d Exposure to gamma radiation kills the microorganisms in food and so delays their decay.3 a iiiWear lead lined clothes, stand behind lead screenWear clothing, use sunblock.4 Type ofradiationx-rayPossible harmcancerPrecautionslead screeningmicrowaves cancermetal screeninginfra-redskin burnsavoid over-exposureultravioletcancer/skin damage glasses, sunblockair (less opticallydense medium)normallight is bent towardsthe normalnormallight is bent away airfrom the normalc As the ray of light enters the glass block, it slowsdown and is refracted towards the normal. As the rayleaves the glass block, its speed increases and it isrefracted away from the normal.dairglassairsin isin 55 3 a n 1.59sin r sin 31 sin i sin 45 0.445b sin r     n1.59r 26.4 11c sin c     0.629n 1.59c 39 4 aCHAPTER 12screenprismredorangeyellowgreenblueindigoviolet1 Your diagram could look something like this:60 60 60 glass (more opticallydense medium)source ofwhite lightband ofcolours(spectrum)b White light is composed of a mixture of colours. Becauseeach colour travels at a different speed through theprism, they are refracted through different angles.5 anormalmore opticallydense mediume.g. glassless optically densemedium e.g. airangle of incidence, i, issmaller than the criticalangle, ci rweak reflected raystrong refracted ray

ANSWERSb7 amore opticallydense mediume.g. glassccweak reflected raylight inless optically densemedium e.g. airrefracted ray runsalong the boundaryangle of incidence, i, issmaller than the criticalangle, ccouter claddingof less opticallydense glassinner core of moreoptically denseglasslight outtotal internalreflectionmore optically densemedium e.g. glassstrong reflected rayiiless optically densemedium e.g. airall the lightis reflectedangle of incidence, i, isgreater than the criticalangle, c6 a If a ray of light travelling from glass or water to airstrikes the boundary between the two at an anglegreater than the critical angle, the ray is reflected bythe boundary and is not refracted. This phenomenonis called total internal reflection.bAAs the fibres are very narrow, light entering the innercore always strikes the boundary of the two glasses atan angle that is greater than the critical angle.b Optical fibres are used in the construction ofendoscopes. Bundles of optical fibres carry light intoand out of a patient’s body. Images of the inside of thebody can be created from the reflected light.c TelecommunicationsCHAPTER 131 a Any suitable instrument, e.g. piccolo, flute, violin etc.b The air column is short/strings are short, and sovibrate quickly, i.e. at a high frequency.c Blow harder/bow the strings more vigorously so thatthe amplitude of vibration is larger.d45 BC2 a An echo is a reflected sound wave.b Sound waves are emitted from the ship and travel tothe seabed. Equipment on the ship detects some ofthe sound waves reflected from the seabed. The depthof the sea can be calculated from the time betweensending the sound wave and detecting the echo.c Distance travelled in 4 s 1500 m/s 4 s 6000 m, sodepth of water 3000 m45 c The final image created by a prismatic periscope islikely to be sharper and brighter than that produced bya periscope, which uses mirrors.AdBCBicycle reflectors and binoculars use prisms to turnlight through 180 .3 a This person cannot hear sounds with frequencies lessthan 20 Hz or greater than 20 000 Hz.b The strings of a violin are shorter and vibrate morequickly.340 m/svc λ   0.005 mƒ 69 000 Hzb λ 3.4m4 a f 100Hz305

306 ANSWERS5 a When the source is vibrating with a small amplitude,the disturbance of each air particle as the wavepasses is fairly small and the sound is quiet. If thesource is vibrating with a large amplitude, the particlesare displaced further from their rest position as eachwave passes, and we hear a louder sound.cmore densly packedair particlesExperimentTime insecondsSpeed ofsound in m/s12.9533923.0033332.9034543.2031352.95339(1 mark for each row of table completed)Average speed of sound from experiment 334 m/s (1)less densly packedair particles5 a Radio waves, microwaves, infra-red waves,visible spectrum, ultraviolet waves, X-rays, gammarays. (2)small amplitudelarge amplitudebd No. The effect of any wind is cancelled out as thesound travels in one direction as it approaches thebuilding, and in the opposite direction as it returns.quietsoundloudsoundEND OF UNIT 3 QUESTIONS1 a Bb D2 ac A (3)λAb All these waves transfer energy (1), are transversewaves (1), travel at the speed of light in a vacuum (1),can be reflected, refracted and diffracted (1).c Radio waves – communication (1); microwaves– communication/cooking (1); infra-red waves –cooker/heater/remote control/night vision (1); visiblelight – seeing/communication (1); ultraviolet waves– fluorescent tubes/tanning lamps (1); X-rays –X-radiography (1); gamma rays – sterilising food orequipment/radiotherapy (1).d Gamma rays (1), X-rays (1) and ultraviolet waves (1).b iiif v / λ (1)20 m/s (1)2.5 s 8 Hz (1)T 1/f 1/8Hz 0.125s (1)3 a A less dense glass, i.e. a glass with a lower refractiveindex. (1)b A more dense glass, i.e. a glass with a higherrefractive index. (1)c The light is striking the boundary at an angle greaterthan the critical angle (1) so total internal reflectiontakes place. (1)d Optical fibres are used in endoscopes. These allowdoctors/surgeons to see inside the body, and makekeyhole surgery possible. (1)The vibrations of a longitudinal wave are alongthe direction in which the wave is travelling (1).The vibrations of a transverse wave are across thedirection in which the wave is travelling. (1)ii Sound waves are longitudinal waves. (1) Lightwaves and surface water waves are transversewaves. (1)b To improve the accuracy of the experiment. (1)4 a ie Radio waves (1), microwaves (1) and visible light (1).sin isin 38n 1.51sin r sin 241ii n     , c 41.3sin c11b n n 1.49sin csin 426 a iUNIT 4 ANSWERSCHAPTER 141 a Stored chemical energy in the battery electricalenergy in the circuit heat and light in the lampfilament.b Stored chemical energy in the paraffin wax heat andlight as the candle burns.c Kinetic energy of moving hands heat energy.d Stored energy in the stretched elastic of thetrampoline kinetic energy of the trampolinistmoving upwards gravitational potential energyas the trampolinist slows to a halt at the top of thebounce.

ANSWERSCHAPTER 152 a1.2 cm3.6 cm1200 J of light3600 J of electricalenergy supplied tothe lamp2.4 cm2400 J of heat1.2 MJof kineticenergyb6 MJ ofheatenergy8 MJ ofelectricalenergy0.8 MJof wastedenergy3 a10 kJ raises thetemperature ofthe kettle400 kJ ofelectrical energysupplied to thekettle350 kJ ofenergy toheat thewater40 kJ escapes tothe surroundings350b Efficiency     0.8754004 a 6 J of energy is converted to heat in the ball and theground and to sound.b10 J ofkineticenergy4 J of kineticenergy6 J ofheat andsound energy1 a Some of the heat energy in the tea is transferred to thespoon. Also, the metal spoon is a good conductor ofheat, so it increases the area from which the heat ofthe tea can be lost.b The plastic lid traps a layer of air above the tea. Airis a poor conductor of heat. The trapped layer of airalso greatly reduces heat loss fr

IGSCE Physics answers ANSWERS 297 UNIT 1 ANSWERS CHAPTER 1 1 8 m/s 2 a10500 m (10.5 km) b105000 m (105 km) c630000 m (630 km) 3 4000s (Snails can actually move faster than this! At a more realistic 4 mm/s (0.004 m/s) it would only take the snail 400 s or 6 minutes 40 seconds.) 4 agraph D bgraph C cgraph A dgraph B 5 distance time