understanding paper 2 section b physics spm

7/29/2019 UNDERSTANDING Paper 2 Section B Physics SPM

1/13

SOALAN UNDERSTANDING

TINGKATAN 4

CHAPTER 1

1. Explain the differences between accuracyand consistency of a measuringinstrument by using suitable examples.

Accuracy is the ability of the instrument togive readings close to the actual value.

The value determined is accurate if it is nearto the actual value

The consistency of a measuring instrument isthe ability of instrument to record consistentreadings for each measurement with littledeviation among readings.

The measurement is consistent if the valuesdetermined are close to each other.

CHAPTER 2

2. What can you say about this antsdistance and displacement?

Distance is the total path length travelled.

Displacement is the distance in a specifieddirection.

The magnitude of the displacement is equalto the shortest distance between two point.

The magnitude of distance is larger thanmagnitude of displacement.

3. To accelerate 2 objects with the sameacceleration, the heavier object needs abigger force. Explain the statement.

Higher mass, higher inertia

Inertia is the property of an object whichresists a change in its motion.If it is at rest ittends to remain at rest , if it is moving it tends

to continue moving.To accelerate an object, need to overcome the

inertia first.

Therefore, more force is needed for heavierobject.

4. Can you explain why the passengerthrown forward when the bus suddenlystop and the head of the passenger werethrown back when the car started moving?

When the bus was moving, the passengerwere also moving at the same speed as thebus.

When the bus stopped, the passengerscontinued moving. Hence, they were thrownfoward.

The people in the car tried to remain in theirstate of rest when the car started moving.Hence, they were thrown back.

In both situations, the passengers wereresisting a change in their state of motion andalso known as Inertia.

The concept of inertia also known as NewtonsFirst Law of Motion, which states that anobject will remain at rest or continue with a

constant speed in a straight line unless anexternal forces acting on it

5. Can you explain why a maximumspeed of supertanker might need to stopits engine over a distance of about 3 kmbefore it can come to stop?

A supertanker at a state of motions and have amaximum velocity.

A supertanker has a larger mass.

A larger mass have a lot/larger inertia.

When the engine stop, the supertanker willcontinue it state of motions.

So it take a longer distance/time to stop due to

its has a larger inertia.

6. Explain why a softball player moveshis hand backwards while catching a fastmoving ball. Other situation: bend ourknee after jump?

A soft ball has a high velocity.

A soft ball has a high momentum.

The soft ball player moves his hand backwardto increase time impact.

The higher the time impact will reduceimpulsive force.

So we will not feel hurt.

7. When the ball on left end of aNewtons cradle is pulled aside (Diagram2.1) and allowed to fall, the ball on thefar end is knocked away from the otherswith the same speed as the first ball(Diagram 2.2).

Explain, in term of momentum and energytransfer, why

the ball on the opposite end is knockedaway from the

others.

When the ball on one end is pulled upand let to fall, it strikes the secondball which is at rest and comes to adead stop.

The momentum of the ball becomes zero as itsvelocity is zero.

The Principle of Conservation ofMomentum states that in a collisionbetween two objects the total

momentum of the objects in thesystem remains unchanged.

The energy and momentum from thefirst ball is transferred to the second

24


2/13

ball and then transmitted throughthe balls at rest to the ball on theother end.

Because the momentum and energy ismaintained in this system, the ball onthe opposite side will move at thesame velocity as the ball that were ininitial motion

8. Diagram (a) shows two identicalspherical plasticine balls before beingreleased from the same height. Diagram(b) shows the state of the plasticineballs when they hit the wood and thesponge. It was observed that theplasticine stopped more quickly when ithit the wood.

Explain the changes in energy that occur

from the moment the plasticine ball isreleased until reaches the position inDiagram (b)

Before released, the plasticine hasGravitational Potential energy .

When falling , Gravitational Potentialenergy changes to Kinetic energy

When the plasticine hits the surface ofwood , the Kinetic energy changes to Heatenergy / / Sound energy

The energy / work done is use to changesthe shape of sponge

9. Explain how the forces between themolecules caused the elasticity when thespring is compressed and stretched.

There are two types of force; attraction andrepulsive force between the particles of thesolid.

When the solid is stretched, the moleculesdisplaced away from each other

Attractive forces are acting to oppose thestretching

When the solid is compressed, the moleculesdisplaced closer to each other

Repulsive forces are acting to oppose the

compression

10. Using the principle of conservation of momentum, explain theworking principle of the rocket.

Fuel burns in the combustion chamber

Hot gases expelled at high speedbackwards

A large backwards momentum is produced

The rocket gains forwards momentum ofequal magnitude

11.Using a catapult(lastik), explain how toenable a stone to travel a longer a longerdistance

Use a thicker rubber to increase theelastic potential energy

Stretch the rubber longer to increase theelastic potential energy

Use a stone with smaller mass to increasethe acceleration of stone

Use a strong material for the handle of thecatapult do not break easily

12. Bowling ball and tennis ball are drop fromthe higher placed. Which ball arrivedfirst?

Although the gravitational force is greateron the heavier body (its weight), the forcealso acts on a greater mass.

A greater mass means a greater inertia.

Therefore the ratio of gravitational force tomass is the same for every object in freefall.

The results are all bodies accelerateequally during free fall.

So, Bowling ball and tennis ball arrived at

the same time.

13.Why the boy with mass 40kg slides downthe flume when the angle of inclination is30 o and remains stationary when theangle of inclination is 17.5o.(the frictionalforce is 120N)

Boy slide down when component of weightparallel to the slope is higher than frictionalforce

Resultant force acting to producedacceleration

Boy remain stationary when component of

weight parallel to the slope is equal tofrictional force

Resultant force is equal to zero make theboy in force equilibrium

14.Explain why the boat moves away fromthe jetty as a boy jumps out of the boatonto the river bank.

When the boy jumps onto the river bank,his momentum is forward.

Using the Principle of conservation ofmomentum

the total momentum before and after

jumping is equal The boat moves backward to balance the

forward momentum

15.Explain why the need of steel structureand the separate compartments to buildin lorry carrying heavy load.

The inertia of lorry and load is very bigwhen it is moving

The separate compartments make the loaddivided into smaller mass, thus reducingthe inertia of each unit.

The momentum of lorry and load is very

big when it is moving and produce a biggerimpulsive force.

The steel structure will prevent the loadsfrom smashing into the driverscompartment during emergency braking.

25


3/13

16.Explain why the hovercraft moves withconstant velocity in terms of the forceacting on it

The forward force = friction // forward thrust= drag

The resultant force is zero

The hovercraft is in force in equilibrium

17. Why we feel easier to pull the wheelbarrow compared to push the wheelbarrow?

The object on the wheel barrow has aweight

When we push the wheel barrow there isforce acting on the ground in the samedirection as the weight.

So the total force acting on the ground arethe weight and the force produced whenwe push the wheel barrow.

When we pull the wheel barrow the forceproduced is in opposite direction with theweight.

So the total force acting on the floor are aweight less the force produced when wepull the wheel barrow

CHAPTER 3

18. Explain why the dam is thicker at thebottom?

Pressure increase with depth

So, pressure at the bottom is higher thanthe surface

Thicker wall is build at the bottom due tohigh pressure.

19. Explain why a soccer player usually wearsshoes with spikes?

Spikes have small area at their ends

Pressure exerted on the ground is high

Spikes sink in the ground

Skidding is prevented

20.Diagram 2 shows two pairs of shoes used bya lady. Explain why shoes in Diagram 2.2is more suitable to used for jogging alongthe beach compared to the shoes inDiagram 2.1

Diagram 2.1 Diagram2.2

The area in contact with the ground for the

shoes in figure 2.2 is larger than the shoes in

figure 2.1. The pressure exerted by the shoes in

figure 2.2 is lower than the shoes infigure 2.1

The shoes in figure 2.2 is difficult to sink into the

ground compared to the shoes in figure 2.1.

So, it is easier to run using the shoes infigure 2.2.

21. Explain how the medicine flows from theIV bottle into the patients vein

Pressure increased with the depth.

Pressure in IV bottle is greater than thepatients vein due to the position ofpatients vein is lower than the IV bottle.

Medicine flowing from IV bottle becauseheight produced difference in pressure//Medicine flow from higher pressure tolower pressure.

This situation also caused by gravitationalpull or weight of liquid.

The concept involve is Pressure In Liquids

22.Explain how to drink the water by usingthe drinking straw?

When we suck through the straw, the air

inside the straw is removed. Produced a partial vacuum area in the

straw

Difference in pressure occurs

Patm is higher than the Pressure inside thestraw

Force is exerted to pushed in the water intothe straw

23. Explain why the wooden block moveupwards and then float on the watersurface when it release from the above ofthe water surface.

Buoyant force increase when the volume ofwater displace increase.

Buoyant force higher than weight of block.

Boyant force pushed the wooden blockupward.

The wooden block then float because thebuoyant force is equal to the weight of thewooden block

The concept involve is archimedes principle

24. Exlplain how the brake system operateswhen the car needs to slow down.

When the brake is pressed ,a force isapplied to the piston and pressure isexerted.

Pressure is transmitted uniformlythroughout the brake fluid.

Force is exerted on the piston of the brakepads

Brake pads will press against the brakediscs.

25. The toothpaste flows out of its tubewhile squeezing at the bottom end

Explain how the toothpaste flows out andname a physics principle related to it.

Force is applied to the toothpaste (tube)

Will produced a pressure

The toothpaste carry the pressure

26


4/13

and apply the pressure of the equalmagnitude to the whole tube

26.Using the physics concepts explain why aboat is at different levels in the sea andin the river, although the boat carries thesame load.

The boat floats, so Weight of the boat =Weight of the water displaced = Buoyantforce

As the weigh of the boat is thesame so the weight of water displaced inthe river and the sea water also thesame

Density of sea water is higher than riverwater

Volume of water displaced in the sea is lessthan in the river,

Level of the boat is higher in the sea than inthe river

27.Explain how a submarine is able tosubmerge into deep sea water?

Valve release air from ballast tank.

Sea water flooded ballast tank

The weight of water displaced is smaller.

Buoyant force < Weight of the submarine

28. Terangkan bagaimana anda bolehmenentukan ketumpatan bagi penyumbatgabus.

timbang jisim gabus

ikat gabus dengan pemberat dan masukandalam silinder penyukat

perubahan isipadu air bersamaan denganisipadu gabus

ketumpatan gabus = jisim perisipadu

29. Explain why a balloon filled with helium gas rises up in the air.

The balloon acted by two forces: Upthrustand the weight of the balloon

The density of helium gas is less than thedensity of surrounding air

Upthrust equals to the weight of the airdisplaced by the balloon

Upthrust is higher than the weight of theballoon

30. Diagram shows a copper block and abowl shape copper sheet of same mass.

Explain why the copper block sink inwater but the bowl shape copper sheetfloats on water

two forces act on the copper block andbowl are uptrust and weight

Uptrust small because small volume // viseversa

The average density of cooper sheet issmaller than density of water. Cooper sheetwill float.

Block sink because weight > uptrust

Sheet float because weight = uptrust

31. Diagram shows a cross-sectional of awing of a moving aero plane. The wing ofthe aero plane experiences a lift force.Explain why the lift force acts on the wing

of the aero plane.

Higher velocity on the upper surface andlower velocity on the lower surface

Thus produced lower pressure on the uppersurface and higher pressure on the lowersurface

Lift force = difference in pressure x area ofsurface

32. Explain the principle of Insect PistonSpray

When the piston is pushed, air is forced outthrough the jet of gas at a high speed.

According to Bernoullis Principle, thepressure of the moving air decreases asthe speed of the air increases

The higher atmospheric pressure in theinsect poison container will push

the insect poison liquid up through thenarrow metallic tube.

33. Explain how the vacuum cleaner is able toremove dust from the floor

the fan blow air out of the vent

produce a partial vacuum area in thevacuum cleaner

difference in pressure occurs/atmosphericpressure is higher than the pressure insidethe vacuum cleander

forced is exerted in/pushed in the dirt.

34.Bunsen burner burning with yellowflame . Explain how a blue flame can beproduced.

27


5/13

High velocity of gas produce low pressureat the jet

Higher atmospheric pressure pushes the airinside and mix with the gas

Complete mixture of combustion willproduce blue flame

Enlarge the orifice to allow more air

35.The roof of a house being lifted by strong

winds. Explain why.

the strong wind above the roof is movingvery fast

While the air in the house is at rest

according to Bernoulli principle the higherthe velocity, the lower the pressure

Pressure inside the house is higher thanthe outside.

a force is generated by the difference inpressure which is strong enough to lift theroof.

CHAPTER 4

36. Explain why a piece of iron becomeshotter than a piece of wood of the samemass when both absorb the same amountof heat.

Substance with higher specific heatcapacity requires more heat to change thetemperature of 1 C

The higher the specific heat capacity, thesmaller the temperature change

Specific heat capacity of wood is higher

If the amount of heat absorb is the same,the change in temperature for wood issmaller

37. Water is used as a cooling agent in aradiator. Explain how water is used as acooling agent in the radiator.

Water has high specific heat capacity

When water in tube passes through theengine it can absorb large amount of heatenergy

Once water reach the radiator, the heat ofthe water absorbed by the fin blade of theradiator

The same time the fan in the radiator pushthe heat out of the car.

38. Explain why the body of a cooking potis made of good heat conductor where thehandle of the pot is made of poor heatconductor?

Good heat conductor has a smaller speseficheat capacity

Hence the body of the cooking pot can beheated up very fast.

Poor heat conductor has a larger speseficheat capacity

Hence the handle may absorb a greatamount of heat without a high increase intemperature or will not become to hot.

39. Terangkan bagaimana proses sejatanmengakibatkan suhu cecair berkurang.

Di dalam air terdapat molekul yangsentiasa bergerak pada halaju berbeza

Dipermukaan air molekul-molekul berhalajutinggi memperolehi tenaga kinetik tinggi

Ikatan antara molekul diatasi dan terbebaske udara

Air kehilangan molekul berhalaju tinggi jadiTK air rendah, suhu berkurang

40. According to the principle of thermalequilibrium and the working principle of

a thermometer, explain how a doctor cancheck his patient temperature duringmedical treatment.

Thermometer is placed in the mouth ofpatient,

Heat is transferred from patients body tothe thermometer.

Thermal equilibrium between thethermometer and patients body is reachedwhen the net rate of heat transfer is zero.

The thermometer and the patients bodyare at the same temperature. Thethermometer

Reading shows the temperature of the

patients body.

41.Explain the changes which occur in theliquid naphthalene when it is cooled untilit changes from the liquid to the solidstate.

As liquid naphthalene cools, it loses energyto surroundings

Its temperature begins to fall until itreaches freezing point 800C

At its freezing point, naphthalene begins tosolidify.

Although it is losing its energy tosurroundings, its temperature remainsconstant because the average kineticenergy remains constant

42. Why the ice cube stick to the wet finger.Not to dry Finger?

Ice cube melt will absorb the heat

The heat is known as latent heat offusion

When our finger wet it has a smallamount of heat and it will absorb by the icecube.

The heat release from water causes

it to be frozen.

So the ice cube and finger will sticktogether due to the frozen of water

28


6/13

Furthermore finger have a roughsurface and it helps the ice stick to ourfinger

43. Apabila beberapa titik ether terkenatangan seorang pelajar, tangannyamerasa sejuk. Terangkan bagaimana iniberlaku.

takat didih eter adalah rendah

suhu tangan lebih tinggi dari suhu eter

menyebabkan haba mengalir dari tanganke eter

eter meruap//membawa haba pendampengewapan

menyebabkan suhu tangan turun danterasa sejuk

44.Your body sweats when you are feelinghot.How does sweating helps to cooldown your body?

When we do the activity using the

movement of our body a sweat will poduce. Acctually water evaporates from the skin

when we sweat.

In the process of evaporation the change ofphase of matter from liquid to steam occur.

The heat is needed to change this phase iscall the latent heat of vapourisation.

So we feel cool when evaporation occurdue to the release of heat in our body.

Factor influence the process: air velocity,temperature and humidity.

45. We cannot use a cooling system of arefrigerator to cool the hot room. Explainwhy?

Cooling system of a refrigerator is smaller

Less cool air from refrigerator flow outcompare to the hot air flow in

Position of refrigerator is on the floor

The cool air does not flow upward

46. Why we put the fishes in the ice cuberather than cold water?

Ice melts need heat known as latent heat offusion

Heat is absorb from the fish. Fish will release it heat until the temperature

equal to 0

Cold water not experience a change of phase

So just the process of thermal equilibriumhappen when they in thermal contact.

The lower temperature not to be 0 degree.

47. Cuaca yang paling sejuk dialami padapenghujung musim sejuk, iaitu apabilasalji mulai melebur. Jelaskan kenapa?

salji perlukan haba untuk melebur

haba tersebut adalah haba pendam tentuiaitu untuk menukarkan fasa pepejalkepada cecair

lebih banyak haba diserap daripersekitaran

48. Using kinetic theory of gasses, explainhow the pressure increase when thetemperature increase in the pressurecooker.

Molecules moving freely in random motion

When temperature increase, kineticenergy//velocity increase

Molecules strike the walls of pressure cooker morefrequently

The rate of change of momentum increase

Force exerted on the walls increase, pressure (P =F/A) increase

49. In the morning feel hot at the sea .Explainwhy this phenomenon happens?

During the day,the land and the seareceive the same amount of heat from thesun

Water has a higher specific capacity thanthe land

The land is heated to a higher temperaturethan the sea

The density of the air above the sea ishigher than the density of the air above theland

The air above the land flows up and the airabove the sea flows towards the land

50. Using kinetic theory of gasses, explainthe changes in volume, pressure andtemperature of the ping pong ball afterboiled water is poured onto it.

When the boiled water is poured onto theping pong ball,

The temperature of the air/gas willincrease/ the kinetic energy increase

The rate of collision betweenmolecules and wall of the ball willincrease so the pressure will increase,

the ball will expand, so the volume willincrease

when the volume increased, area ofcollision increased, so lastly the pressurewill remain the same

29


7/13

51.Explain why the air pressure in the tyreincreases when more air is pumped into itand after the car has completed a long

journey

The number of molecules per unit volumeincreases

The number of collisions per unit time

increases / rate of collisions increases The temperature of the air molecules

increases, the kinetic energy of the airmolecules increases

The force exerted on the tyre increases

CHAPTER 5

52. Diagram 7 shows the superior mirage which occurs over cold water surface andsnow.

Using physics concepts, explain why theobserver can only see the image of theship.

The air close to the surface is much colderthan the air above it.

Light travels from denser to less densemedium

Light rays refracted away from normalline and bent downward toward thesurface

thus tricking our eyes into thinking anobject is located higher in appearancethan it actually is

the observer will see the image of the shipdue to light travels in a straight

53.Tousrist at a beach observing the sunset.Explain why the tourist can still able tosee the sun even though it has alreadyset.

Refraction of light ray occurs

Light travels from less dense to adenser medium

The light will bend towards thenormal

In the observer eyes, the sun isstill not setting as they can still see theimage from refraction

54. While driving a car on a hotday, you may see a mirage on the road.Explain how mirage occurred.

The layers of air nearer the road warmer.

The density of air decrease nearer to theroad surface.

The light travel from denser to less densearea.

The light refract away from the normal

When the angle of incidence exceed thecritical angle, total internal reflectionoccurs

55. Diagram shows a ray of light directedperpendicularly at a side of the semicircular glass block. The ray passesthrough the glass block to a point O

before leaving the glass block. The angleof incidence in the glass block is 30

Explain how total internal reflection occurs indiagram above?

Increase the angle of incidence,i then angleof refraction,r will also increase

Keep on increasing the angle of incidenceuntil angle of refraction is 90

The angle of incidence is called criticalangle

Increase the angle of incidence more thanthe critical angle, the ray will be reflected.

56. Diagram 6 shows Ali standingat the side of a pond. Ali can see theimage of the fish and the image of thedragon-fly in the water as shown by theray diagram.

By using physics phenomenon explain how Alican see the image of the fish and the image ofthe dragon-fly..

For the fish, the light is refracted / changedirection at B.

the light is refracted away from normal,towards the observers eyes

For the dragon-fly, the light is reflected bywater surface at A.

Reflected angle = incidence angle,reflected towards the observers eyes

57. Explain why the diamond issparkling when the ray of light passthrough

30

Diagram 6

Cool water


8/13

Diamond mempunyai indeks biasan yangtinggi

Sudut kritikalnya sangat kecil

Permukaan diamond dipotong supayasudut tuju cahaya lebih besar berbandingsudut kritikalnya

Cahaya yang melalui diamond akanmengalami fenomena pantulan dalampenuh beberapa kali menyebabkan banyak

alur cahaya bersilang-silang di dalamdiamond tersebut.

Jumlah alur cahaya yang banyak yang tidakdapat keluar menyebabkan diamond dilihatlebih bercahaya.

58. Explain why a piece of paperburns when placed under a convex lensaimed towards hot sun rays.

The parallel rays of the sun will passthrough the a convex lens

After entering the lens, the light rays isfocused at the principal focus of the lens

At the principal focus, the light ray isfocused on one small area

Heat energy causes an increase intemperature, the paper starts to burn

59. Explain how you would estimate the focallength of a convex lens in your schoollaboratory .

The convex lens is aimed/focused to adistant object (infinity)

The screen is adjusted until a sharp imageis formed on the screen

The distance between the screen and thelens is measured

Focal length = distance between thescreen and the lens

60. It is known that the sky is red duringsunset and the formation of rainbow onthe sky always appeared after raining.Explain these phenomena.

Light consisting of seven colours.

Red has the longest wave length and thelast to refracted during sunset.

A droplet of water trap in the atmosphere

after raining acts a lens. Light travel through this water droplet and

undergo the process of refraction ,totalinternal reflection and dispersion of lightoccurred.

61. You are given two convex lenses S and Qwhere lenses S has longer focal lengththan lens Q. Using this two lenses explainhow are you would make a simpleastronomical telescope

Choose lenses S as objective lenses

Choose lenses Q as eyepiece

Lenses S is placed in front of lenses

Q

The two lenses are adjusted so thatthey are in normal adjustment where

distance between the two lenses is eaual to(fo + fe)

TINGKATAN 5

CHAPTER 6

62. At the start, the pendulum oscillates withmaximum amplitude. The amplitude ofthe oscillation decreases with time andfinally stops. What courses the pendulumto stop?

When the pendulum oscillates, it hasenergy

This energy is used to overcome airresistance

and energy also lost from the system inform of heat

As time passes, more energy of thependulum is being used to overcome airresistance.

This courses the energy of the pendulum todecrease

As a result, the amplitude becomes smaller

The pendulum is said to experiencedamping

63. Two identical tuning fork have the samenatural frequency. Only the first tuningfork is made to vibrate but why thesecond turning fork also start to vibrate?

As the first fork begins to vibrate, thesurrounding air molecules will begin tovibrate with the same frequency

Energy is transferred to the second forkcausing it to vibrate at its naturalfrequency

When this happens the seconds tuning fork

is said to resonate with the first tuning fork When resonance occurs, the tuning fork

vibrate at maximum amplitude andproduce the loudest sound.

64. Diagram 10 shows the pattern of seawaves when approaching the beach.

Explain in terms of the wave phenomena,why the water waves follow the shape of the

31


9/13

beach as it approaches the shore.

waves move from deeper to shallow area

the speed decreases

the wave refracted towards the normalline

the wave front which perpendicular to thedirection of propagation of waves resultingthe wave front following the shape of thebeach

65. During high tide (air pasang), a boatwhich parks behind a retaining wallrocking up and down more vigorously.Explain the statement.

When depth increase,

Velocity will increase,

Wavelength increase and

Higher degree of diffraction happen

66. Explain why water wave is calmer at thebay then at the cape

waves move from deeper to shallow area

the speed decreases // the wave refractedtowards normal line

the depth at cape decreases abruptlyresulting waves focused at cape

the depth at bay decreases slowlyresulting waves spread out

the energy of waves is smaller at bay resultingcalmer region compared to at cape

67. When two spherical dippers vibrates on awater surface, a wave pattern ofinterference is produced.Explain why the water level in the rippletank must be at constant depth duringthe experiment.

Wave length depends on depth of water

Increasing/decreasing of depth will causethe wave to refract

Refraction will increase/decrease thelength of wavelength

The nodal/antinodal line will be affected

68. The sound wave from the train(etc) canbe heard loudly and clearly at night. Why?

Air near the ground colder tha above air

Air layer the ground more denser

Sound travel slower in cold air/wavelengthdecrease in cold air

Sound bend toward the observer/soundbend away to normal

69. Explain how the sound wave is used todetermine the depth of an ocean.

Use ultrasound, ultrasound is transmittedto the sea bed

a receiver will then detect the reflectedpulses

the time taken by the pulseto travel to the seabed and return tothe receiver being recorded, t

the depth of the sea can be calculated using theformula, d = vt/2

70. Explain why strong double-glazed glass isused as walls of the observation tower inan airport.

All particles in a material/matter/glassvibrate at its natural frequency

The airplane engine produces noise whichcause the air to vibrate

Due to resonance, the glass vibrate at ahigher/maximum amplitude

Need strong glasses to withstand the effectof resonance which vibrate with highamplitude

so that it does not brek easily71. How can when the opera singer sing can

make the glass break.

The singer sing with a certain frequencyand produce sound energy

The energy is transferred to the glass

Resonance occures when the forcedfrequency made by the singer is the sameas the natural frequency of the glass

The glass will vibrate with maximumamplitude

Increase in energy transferred may causethe glass to break

72. Descibe the movement of two similiarships that are located at A and B. Explain?

The ship at A will move up anddown

Because constructive inteferencehappens at point A

The ship will remain calm atlocation B

Because destructive inteferencehappens at point B

CHAPTER 7

73.Explain the advantages of parallel circuit ina house wiring system.

A parallel circuit can run severaldevices using the full voltage of thesupply.

If one device fails, the others will

continue running normally A failure of one component doesnot lead to the failure of the othercomponents.

32


10/13

More components may be added inparallel without the need for more voltage.

Each electrical appliance in thecircuit has it own switch

Less effective resistance of thecircuit

74. The graph shows of potential difference,V, against current, I, for a filament lamp.

What happens to the resistance of thefilament when the current increases?Explain your answer.

The resistance of the filament increases

The higher the current, the higher thetemperature of the filament bulb

As the current increases, the gradient ofthe graph / the ratio of the voltage andcurrent increases

Resistance is the gradient of the graph

75.Explain why a three pin plug is moresuitable compared with a two pin plug.

Two pin plug has no earth wire while threepin plug has earth wire

Using 2 pin plug, if there is leakage ofcurrent it will also flow through the metal

body while using 3 pin plug if there isleakage of current it will flow to the ground

The person who touches the metal bodywill experiences electric shock while using3 pin plug, the current will be earthed

Using 2 pin is not safe to the consumerwhile using 3 pin plug is more safer to theconsumer

76.Explain why it is more dangerous to touchthe live wire of mains supply, rather thanthe neutral wire.

Our bodies are at earth potential(0V)

If we touch the live wire, there willbe a large potential difference between livewire and our body

A large current will flow through it,probably fatal (menyebabkan kematian)

The neutral wire stays at earthpotential (0V), roughly at the samepotential as our body.

If we touch the neutral wire, thereis no potential difference across us and sono current flows

77. What happen to the candle flame when itplace between 2 metal plate supply withExtra High Tension (EHT).

The lighted candle / the heat from thecandle causes the air molecules to beionized.

The positive charges would beattracted to the negative plate and/or thenegative charges would be attracted tothe positive plate

The flame of the candle would be

dispersed (flattened) into two parts //suitable diagram

Positive charges are heavier thannegative charges

More of the flame is attracted to thenegative plate

78. Pembakar roti T bertanda 240 V, 650 Wdan pembakar roti U bertanda 240 V, 840W. Tentukan pembakar roti yangmanakah mempunyai elemen pemanasdengan rintangan yang lebih kecil.

pembakar roti U

kedua-dua pembakar roti mempunyaivoltan kerja yang sama

kuasa elemen pemanas = V2/R //kuasaelemen pemanas berkadar songsangdengan rintangan

pembakar roti dengan kuasa yang lebihtinggi mempunyai elemen pemanasdengan rintangan yang lebih kecil

79. Explain why the bulb connected to twodry cells lights up brighter than one bulbconnected to one dry cell.

The two dry cells are connected in parallel The effective e.m.f. remains the same

The effective internal resistance of the two cells issmaller

A larger current will flow through the bulb to makeit brighter

80. Sebuah bateri yang terdiri daripada duabuah sel kering berlabel 1.5 Vdisambungkan kepada sebuah mentol2.5V 0.3 A. Didapati bahawa mentol itumenyala dengan kecerahan normalapabila suis dihidupkan. Terangkanmengapa mentol itu menyala dengan

kecerahan normal walaupun d.g.e baterilebih besar daripada voltan metol itu.

bateri mempunyai rintangan dalam

sebahagian daripada d.g.e bateri hilang didalam bateri/sebahagian digunakan untukmengatasi rintangan dalam

voltan//beza keupayaan yang dibekalkankepada mentol hampir sama dengan voltankerja mentol

CHAPTER 8

81. The acceleration of a magnet that drops

vertically into a solenoid is much smallerthan the gravitational acceleration.Explain the statement.

Magnetic flux change in the solenoid

33


11/13

Induced current generates in the solenoid

Direction of induced current always flows inthe direction to generate magnetic pole tooppose the pole of the falling magnet.

Therefore, acceleration is lower

82.Explain how the electromagnet crane can be usedto lift scrap metal.

Current flow through the solenoid,magnetic field is produced

Soft iron core will be magnetized

The scrap metal attracted to the iron core

No current flow soft iron demagnetized ormetal scrap fall down

83. Most of our electric energycomes from hydroelectric power stationsand thermal power station. These powerstation are connected by cables totransmit electricity to users in industries,

offices, schools and houses. This systemis called the national grid network.Explain briefly the importance of thenational grid network system indistributing electric energy to the users.

The electrical supply is continuous,although there is faulty in one of the powerstation

The electrical energy from other station isdirected to the affected areas

The electrical energy from other area isdirected to the areas that need moreenergy

The overall cost of production of electricitycan be reduced

84. Diagram shows the pattern ofmagnetic field formed when currentflows in a coil.

Explain why the magnetic field strength isgreater at the center compared to the edge.

The direction of the magnetic field on the left coil isanti clockwise

The direction of the magnetic field on the right coilis clockwise

As the result the magnetic fields in the middle ofthe coil are in the same direction, ie upward.

So the magnetic field will be stronger in the middle.

85. Using the concept of the magnetic effectof an electric current, explain with theaid of diagrams how forces are producedon a wire in the coil of direct currentelectric motor?

The (magnadur) magnets produce a

magnetic field / diagram The current in the wire produces a

magnetic field / diagram

The two magnetic fields interact/combineto form a resultant / catapult field /diagram

The motor will rotate due to the differencesof force produce//turning effect from thistwo forces

86. Explain how the generator works toproduce direct current.

rotate the coil in clock wise direction

the coil cut across the magnetic field

current is induced in the coil

the commutator change the direction inthe coil so that the direction of current inexternal circuit always the same.

87.

Explain how induced current is produced atsecondary circuit?

When an ac current flows in the primaycoil, an altenating magnetic field to be setup inside the iron core

The altenating magnetic field lines in theprimary coil cut the secondary coil, ane.m.f is induced in it as to oppose thechange of the magnetic flux which cousingit

The induced e.m.f will produce an inducedcurrent at the secondary coil

88. Explain how the circuit breakerworks.

When a high current flow, the magneticfield becomes stronger

Electromagnet attracts the soft ironarmature.

Spring P pulls the wire and break the

34

S N


12/13

contact, the current does not flow // thecircuit is disconnected.

When reset button is pressed, springQ pulls the soft iron armature back to itsoriginal Position

89. Explain the working principle of a transformer.

When a.c. voltage is supplied to primarycoil, (alternating current will flow) and

the soft iron core is magnetized.

The magnet produced varies in magnitudeand direction.

This causes a changing magnetic flux passthrough the secondary coil.

An induced e.m.f. across the secondary coilis produced

90.Explain the working principle of anelectric bell.

When the bell is pressed, a currentflows in the coils of the electromagnet,causing the electromagnet to bemagnetized.

The magnetized electromagnetattracts the soft-iron armature, causing thehammer to strike the gong.

The movement of the armaturebreaks the circuit and causes theelectromagnet to lose it magnetism.

The light spring pulls the armatureback, remaking the contact and completingthe circuit again.

The cycle is repeated so long asthe bell push is pressed and continuous

ringing occurs.

CHAPTER 9

91. A semiconductor diode is made fromcombination of an n-type semiconductorand p- type semiconductor. Explain howan n-type semiconductor is produced.

intrinsic semiconductor such as silicon atom

doped with pentavalent atom such asphosphorous

each pentavalent atom contributes onefree electron and there is an excesselectron

the excess free electrons become negativecharge carrier in n-type semiconductor

92.

Diagram 19 shows a circuit consisting of adiode and a bulb. Explain how the bulbwill light up?

Anode of diode (p- type) connected topositive terminal of battery/ foward bias

Electron from n-type drift to p-n junction

towards positive terminal Holes from p-type drift across p-n junction

towards negative terminal

Movement of electrons and holesproduced current, thus the bulb lights up

93.Explain how the green shadow producedin the CRO screen?

6V heater supply produced electron on itsurface

When 3 kV power supply are connectedCathode rays/electron acceleratel in astraight line.

Cathode rays carry kinetic energy and

converts to light energy when they hit thescreen .

94. Explain why the bulb light up at night

At night resistance LDRincreases

VBE increases (higher than 0.7V for Si)

Ib increases and switch on transistor

Ic, increases and lights up bulb

CHAPTER 10

95. Radioisotope Strontium-90 is used tomeasure the thickness of paper in apaper industry Explain how Strontium-90 is used to measure the thicknesspiece of paper?

Put the radioactive source opposite thedetector

Detector is connected to the thicknessindicator

Detector detect the reading of the changesin counts

Thickness is measured with the thicknessindicator

35


13/13

If the reading of the detector is less thanthe specified value, the thickness of thepaper

is too tick/ vice versa

96. Nuclear fission produces a chain reaction.

Describe how the chain reaction occurs in anuclear fission of an atom of Uranium- 235.

Neutron bombarded a uranium nucleusand produced three neutral neutron

The new neutron bombarded a newuranium nucleus

For every reaction, the neutrons producedwill generate a chain reaction

Diagram of chain reaction

97.Runut alfa yang diperhatikan di dalamkebuk awan resapan adalah lurus dan tebal.

Jelaskan bagaimanakah runut alfa terbentukdan mengapakah runut itu tebal dan lurus.

Zarah mengionkan molekul-molekul udara

Wap lampau tepu memeluwap pada ion-ionyang terbentuk

Runut tebal disebabkan kuasa pengionanzarah alfa adalah tinggi//zarah alfamenghasilkan banyak ion.

Runut lurus kerana zarah alfa mempunyaijisim yang lebih tinggi

98.Explain how radioisotopes can be used todetect the location of the leakage

Radioisotope is injected into the pipe

The water in the pipe flow with theradioisotope

G-M tube as detector is used to find theleakage across the pipe

Reading on detector increases when near aleakage

99. Explain how the GM tube is able to detectthe radioactivity radiation

Radioactive ray enter the tubethrough the mica window

ionizes argon gas under lowpressure

The ions accelerate towardsrespective electrodes

Produce a current pulses

Pulses are recorded by ratemeter

100. Explain about to date an archeological

specimen by carbon dating method

Living plants take up the carbon-14 in thecarbon dioxide they use for photosynthesis, asdo animals when they eat the plants for food.

While the plant or animal is alive, theproportion of cabon-14 to ordinary carbon-12 intheir tissues stays constant,

but once they die, the carobn-14 begins todecay

Carbon-14 has a half-life 5 700 years

To date an archeological specimen , a smallsample of carbon is extracted from it

36

understanding paper 2 section b physics spm

Documents