FIZIKMOZAC 2010

CHAPTER 8:ELECTROMAGNETISMANSWER

8.1 ELECTROMAGNETISM1.

(b)(i)

(b)(ii) P: north S: south(b)(iii)

2.(a)(i) X: contact

Y: batteryZ: switch

(a)(ii) soft iron core(a)(iii) easy to magnetized and

demagnetized.(a)(iv) to avoid direct contact with the

circuit with high voltage which isdangerous.

3. Question 8: SBP 08(a) show the direction of current

(b)(i) North pole(b)(ii) Right hand grip rule(b)(iii) diagram above

Draw the pattern correctly Draw the direction of magnetic

field(c)(i0 Soft iron core(c)(ii) can be easily magnetized and

demagnetized.(c)(iii) U-shaped core(c)(iv) strenght of electromagneti is

higher.(d) working principle of electric bell: When the switch is pressed, the

circuit is closed Current flow through solenoid,

the iron core is magnetized. Soft iron core is attracted to the

electromagneti Strike the gong.

4.(a) (b)

FIZIKMOZAC 2010

(c) When the switch is on, current

flow through the copper rod andproduce magnetic field.

The interaction between themagnetic field from thepermanent magnet with themagnetic field from currentcarrying conductor

Produce resultant force Use Fleming’s Left hand rule to

determine the direction of theforce, F

(d)(i) The copper rod will move further.Current increases whenresistance decreases.

(d)(ii) The copper rod vibrate at theequilibrium position.The direction F changes when thedirection of current change.

(e) electric motor, galvanometer.

5.(a) P: commutator

Q: carbon brush(b) P: reverse the direction of current

in the coil every half rotation sothat the coil continues to turn insame directionQ: to contact with thecommutator so the current fromthe battery enters the coil.

(c) SVUT(d)(i) SV: move downwards(d)(ii) UT: move upwards(d)(iii) Fleming’s Left Hand Rule(e) anti clockwise6.(a) magnadur magnet(b)(i)

When the switch is on, currentflow through the copper rod and

The interaction between themagnetic field from thepermanent magnet with themagnetic field from current

Use Fleming’s Left hand rule todetermine the direction of the

ill move further.Current increases when

The copper rod vibrate at the

The direction F changes when thedirection of current change.electric motor, galvanometer.

reverse the direction of currentin the coil every half rotation sothat the coil continues to turn in

commutator so the current fromthe battery enters the coil.

(d)(iii) Fleming’s Left Hand Rule

(b)(ii) wire X moves to the left.Resultant force acts on the wire.

(c) 1. Reverse the terminal of thebattery

2. reverse the polarity of themagnet.

7. Question 5: Pahang 08(a) copper wire moves upward(b) Fleming’s Left Hand Rule(c)(i) The copper wire moves

downward(c)(ii)

(c)(iii) Increase the current and thestrength of the magnetic field

(b)(ii) wire X moves to the left.Resultant force acts on the wire.1. Reverse the terminal of the

2. reverse the polarity of the

7. Question 5: Pahang 08copper wire moves upwardFleming’s Left Hand RuleThe copper wire moves

(c)(iii) Increase the current and thestrength of the magnetic field

FIZIKMOZAC 2010

8.(a)

(b)(i) ac current(b)(ii) When the switch is on, current

flow through the copper rod andproduce magnetic field.

The interaction between themagnetic field from thepermanent magnet with themagnetic field from currentcarrying conductor

Produce resultant force Use Fleming’s Left hand rule to

determine the direction of theforce, F

(b)(iii)The spring produce the sameforce but with opposite direction.

9. Question 8: MRSM 08(a) Electromagnet is a magnet in

which a magnetic field isproduced by the flow of electriccurrent.

(b)(i) Thick Because less resistance

(b)(ii) Soft iron Because easy to magnetise

and demagnetize.(b)(iii) Larger

Because the strength ofelectromagnet increases /stronger magnetic field.

(c) The most suitable is M(d)(i) Parallel to the galvanometer(d)(ii) Less effective resistance(d)(iii) VR = VG

(IR)R = (IR)G

(1 – 0.005)(R) = (0.005)(5)R = 0.0251 Ω

When the switch is on, currentflow through the copper rod and

The interaction between themagnetic field from thepermanent magnet with themagnetic field from current

e Fleming’s Left hand rule todetermine the direction of the

The spring produce the sameforce but with opposite direction.

Electromagnet is a magnet inwhich a magnetic field isproduced by the flow of electric

Because less resistance

Because easy to magnetise

Because the strength ofelectromagnet increases /stronger magnetic field.

The most suitable is Mlvanometer

Less effective resistance

0.005)(R) = (0.005)(5)

10. Question 7: MRSM 09(a)(i) d.c motor(a)(ii)

Reverse the direction of currentin the coil every half rotation sothat the coil continues to turn insame direction

(b)(i)(ii)

(b)(iii)

Current Strength of magnetic field

(c)(i) Change commutator with apair of slip rings

(c)(ii)

Use a curve magnet Magnetic field is

concentrated

8.3 ELECTROMAGNETIC INDUCTION

11.(a)

(b) Fleming’s Right Hand Rule(c)(i) decreases(c)(ii) Increases(iii) No induced current / zero

12.(a)

S

10. Question 7: MRSM 09

everse the direction of currentin the coil every half rotation so

continues to turn in

of magnetic fieldChange commutator with apair of slip rings

Use a curve magnetMagnetic field isconcentrated

8.3 ELECTROMAGNETIC INDUCTION

Fleming’s Right Hand Rule

No induced current / zero

S

FIZIKMOZAC 2010

(ii) Increase the speed Increase the strength of magnetic

field Increase the number of turns of

the coil

13. Question 2: Melaka 09(a) Electromagnetic induction(b) North(c)(i)

(c)(ii)

14. Question 4: Kelantan 08(a) A proces of producing electric

current by changing magneticfield

(b)(i) Cut the magnetic field Induced current is produced.

(ii) A : northB : south

(c)(i) increases(ii) The magnitude of induced

current increases // the rate ofchange of the magnetic fluxincreases

15. Question 6: SBP 07(a) Induced current

(b)(i) Number of turns in Diagram 6.1is greater.

Angle of deflection forgalvanometer in diagram 6.1 isbigger.

(ii) as the number of turnsincreases, the rate of change ofmagnetic flux increases

Increase the strength of magnetic

Increase the number of turns of

Electromagnetic induction

roces of producing electricby changing magnetic

the magnetic fieldcurrent is produced.

The magnitude of inducedcurrent increases // the rate ofchange of the magnetic flux

Diagram 6.1

Angle of deflection forgalvanometer in diagram 6.1 is

as the number of turnsincreases, the rate of change of

increases

hence, induced more current(c) Lenz’s law(d) The current induced p

north pole on the left side so as to oppose the oncoming

magnet

16. Question 6: Kedah 07(a) The current that induced by

electromagnetic inductions whenthe circuit is complete//Thecurrent that can be producedwithout any electricalsupply/source

(b)(i)

X: NY: S

(b)(ii)

Diagram 6.1 bar magnettowards the solenoid

Diagram 6.2 bar magnet awayfrom the solenoid

(c)(i)

When the bar magnet ispushed towards the solenoid,the end of the solenoid facingthe bar magnet has the samepolarity as the bar magnet

When the bar magnet is pulledaway from solenoid, the end ofthe solenoid facing the barmagnet has the oppositepolarity as the bar magnet

(ii) Lenz’s Law(d) Increase the speed of bar

magnet/ increase the number of turns

of the solenoid/ use a stronger magnet

17.(a) Electromagnetic induction(b) WXYZ(c)

hence, induced more current

The current induced producesnorth pole on the left sideso as to oppose the oncoming

Question 6: Kedah 07The current that induced byelectromagnetic inductions whenthe circuit is complete//Thecurrent that can be producedwithout any electrical

Diagram 6.1 bar magnettowards the solenoidDiagram 6.2 bar magnet awayfrom the solenoidWhen the bar magnet ispushed towards the solenoid,the end of the solenoid facingthe bar magnet has the same

larity as the bar magnetWhen the bar magnet is pulledaway from solenoid, the end ofthe solenoid facing the barmagnet has the oppositepolarity as the bar magnet

Increase the speed of bar

increase the number of turnsf the solenoid/

use a stronger magnet

Electromagnetic induction

FIZIKMOZAC 2010

8.4 TRANSFORMER

18. Question 3: Negeri 9 09(a) Step down transformer(b) Direction and magnitude of ac

current always change, so therewill be changing of magnetic flux.

(c) VP = NP = 240 = 20Vs NS 12 1NP : NS = 20: 1

(d)(i) The light bulb does not light up(ii) Dc current has constant

magnitude and direction so thereis no changing in magneticflux/field.

19. Question 4: Johor 07(a) Increase the number of

turns in the secondary coil Decrease the number of turns in

the primary coil.(b) Because iron can be magnetized

and demagnetized easily(c)(i)

P = VI36 = 24ICurrent in the secondary coil = 1.5A//

(c)(ii)

VsIs=VpIp(36) = (240)IpCurrent in the primary coil = 0.15A

20. Question 6: Teknik 07(a) For transformer P, Ns < Np OR

For transformer Q, Ns > Np

(b) For transformer P, Vs < Vp ORFor transformer Q, Vs > Vp

(c)(i)

When Ns < Np , therefore Vs < Vp

(c)(ii)

P : Step – down transformerQ : Step – up transformer

(d)(i)

Alternating current (a.c. )

(d)(ii)

The transformer does notfunction/Output voltage is zeroNo magnetic field induce thecurrent

21. Conceptual: Perak 07(a) Electromagnet is an iron core

which can be magnitized whencurrent flow.// temporallymagnitized when current flowthrough it.

(b) number of turns in solenoid inDiagram 10.1 is more

the magnitude of current flowingin Diagram 10.1 is bigger

the number of paper clipsattracted to solenoid inDiagram10.1 is more

(c)(i)

the strength of the magnetic fieldincreases when the magnitude ofcurrent increases

(c)(ii)

the strength of the magnetic fieldincreases when the number ofturns in solenoid increases

22. Conceptual: MRSM 07(a)(i)

A region where a magnetic materialexperiences magnetic force.

(a)(ii)

When the magnet bar/wire isstationary, the pointer of thegalvanometer does not deflect /shows no reading

When the magnet bar movestowards the solenoid, thepointer of the galvanometerdeflects / shows reading

When the wire moves betweenthe poles of the permanentmagnet, the pointer of thegalvanometer deflects / shows areading

When a wire moves and cut themagnetic field lines, an inducedcurrent flows.

Electromagnet induction

FIZIKMOZAC 2010

23. Understanding: Perak 07 When the switch is on, the soft iron

core becomes electromagnet. End Abecomes north pole.

End B becomes south pole Magnet P repels from end A Magnet Q attracts to end B

24. Understanding: MRSM 07 D.c generator has commutator A.c generator has slip rings D.c current flows in one direction

while a.c current changes directionand magnitude

Kinetic energy changes to electricenergy for both generator

25. Understanding: SBP 07(i) A transformer is a device that

steps up or steps down the voltageof an alternating current. [1]

(ii) Transformer QNs>Np

(iii) Heating effect in the coils Eddy currents in the coils Leakage of magnetic flux The magnetisation and

demagnetisation of the core

Maximum 3

26. Qualitative problem: Perak 07(i) when the switch is on, current

flows in the solenoid, soft ironcore becomes electromagnet

electromagnet attracts the ironarmature, the hammer hits thegong and bell rings

when the hammer movestowards the gong, the contactsopen, current stops flowing

The iron core loses its magnetic(ii) increase the number of turns of

wire the magnetic field produced by

each turn overlap to produce aresultant field which is muchstronger.

Increase the magnitude of thecurrent / dry cells

To increase the strength of themagnetic field

Replace the straight iron corewith a U-shaped iron core

Produce stronger magnetic field

27. Qualitative problem: MRSM 07(i) Draw diagram

Iron core Input 240 V a.c Primary coil 50 turns Secondary coils 100 turns

By using a laminated core To reduce eddy current By using low resistance wire

made of a good conductor To reduce heating effects in the

coils By winding the secondary and

primary coils on top of eachother

To reduce leakage of magneticfield

By using soft iron core Easy to magnetized and

demagnetized.

28. Making Decision: Teknik 07(i) Q

Uses alternate current because itvoltage can be decreased orincreased by transformer

Use high voltage so the currentin the cables is smaller and theloss of power due to heating of

the cables is minimized.

FIZIKMOZAC 2010

(ii)Characteristics Reason

Thick cable Low resistanceLow density Cable is lighterLow rate ofexpansion

Cable does notexpand easilyduring hot day.

Choose cable Z Because it is thickcable, low densityand low rate ofexpansion

29. Making Decision: SBP 07Characteristic Explanation

Low resistivity To reduce heat lossin the cables

Low density The cables will belighter

Low cost Cost of project willbe lower

Low rate ofthermalexpansion

The cables will notexpand under hotweather

• Cable Q• Low resistivity, low density, low cost,low rate of thermal expansion

30. Quantitative problem: SBP 07

(i)Vs = Ns Vp = 500 x 240

Np 2000

= 60V

(ii)Vs = 1000 x 110

500= 220 V

31. Quantitative problem(i) P = VI

I = 15000 = 62.5 A240

(ii) Ploss = I2R = (62.5)2(3) = 11,718.75 W

(iii) 11,718 x 100% = 78.12%15000

32. Section C: Trengganu 07(a) Electric energy to sound energy(b)

Characteristics ReasonSize of thehammer is big

Surface area ofcontact is big

Larger distancebetween thehammer and thegong

The force appliedon the gong isgreater

The number ofturns of the coilsis greater

The strength of theelectromagneti isgreater

High curvature ofthe gong

The area of airmolecule vibrate isgreater

QSize of the hammer is big, Largerdistance between the hammer and thegong, The number of turns of the coil isgreater, High curvature of the gong

(d)(i) I = 10/120.83 A

(ii) PI = 10 x 100%80

= 12.5 W

I = 12.5 = 0.052 A240

33. Section B: Kelantan 08(a) A resultant field due to the

combination of the magneticfield due to the current in theconductor and externalmagnetic field // Diagram

(b) Number of magnet in D10.2 isbigger

angle of deflection of theammeter indicator in D10.2 isbigger

the angle of deflection of thecooper wire in Diagram 10.2 isbigger

the strength of the magnetic

FIZIKMOZAC 2010

increases as the number ofmagnet increases.

the angle of deflection ofcopper wire is increases as thestrength of the magnetic forceincreases.

(c)(i)

Force acting on the cooper rod moved the cooper rod towards

the magnet // left(c)(ii)

the cooper rod vibrates as current change direction

(d)(i)

When the current flow into thecoil, magnetic field isproduced.

Catapult field is producedwhen the magnetic field frompermanent magnet and fromcurrent carrying conductorinteract

A couple of forces areproduced in the oppositedirection

These pair of forces producethe turning effect on the coil.

(d)(ii)

Increase the strength ofmagnet / add more magnet

increase the strength ofmagnetic field

Increase the number of turns inthe coils

to increase the magnitude offorce

Increase the magnitude ofcurrent

to increase the magnitude offorce / increase thestrength of magnetic field

34. Section C: Kedah 08(a) Direct current is current that

flows in one direction.(b) The magnadur magnets

produce a magnetic field /diagram

The current in the wireproduces a magnetic field /diagram

The two magnetic fieldsinteract / combine to form anon-uniform magnetic field orcatapult field.

(c) Low density Coil has smaller mass / lighter High number of turns Larger force acting on the coil /

higher electromagnetic fieldstrenght.

High strength magnets Large force acting on the coil More segments Coil rotates smoothly Choose R Because it lowest density, high

number of turns, high strengthmagnets and many number ofsegments of the commutator.

(d)(i)

3 x 8 = 24 J

(ii) 24/5= 4.8 W

(iii) Efficiency = (4.8/12) x 100%40 %

FIZIKMOZAC 2010

35. Section B: Melaka 08(a)(i)

Magnetic field is a regionmagnetic force.

(a)(ii)

The direction of the mfield on the left coil iscounter/anti clockwise,/diagram

The direction of the magneticfield on the right coil isclockwise // diagram

As the result the magneticfields in the middle of the coilare in the same direction,upward. So the magnetic fieldwill be stronger in the middle

(b)(i)

Both diagram 9.2 and diagram9.3 have the same pattern of themagnetic field,ie, circular withthe wire in the middle

The direction of the magneticfield for Diagram 9.2 isclockwise, while in Diagram9.3is counter clockwise/ anticlockwise.

(b)(ii)

The pattern of the magnetic field inDiagram 9.4 is not uniformcompared to Diagram 9.2 andDiagram 9.3

(b)(iii

The resultant force acting on theleft wire is downward while theresultant force acting on the rightwire is upward / opposite to eachother.

(b)(iv)

Instrument which uses thesame principle is electricalmotor.

The electric motor has 2forces acting on the oppositeside caused by the counterreact between a currentcarrying conductor in amagnetic field/ diagram

Magnetic field is a region of

The direction of the magneticield on the left coil is

clockwise,

tion of the magneticfield on the right coil is

As the result the magneticfields in the middle of the coilare in the same direction,

So the magnetic fieldwill be stronger in the middleBoth diagram 9.2 and diagram9.3 have the same pattern of the

,ie, circular withthe wire in the middleThe direction of the magneticfield for Diagram 9.2 isclockwise, while in Diagram9.3

counter clockwise/ anti-

The pattern of the magnetic field inDiagram 9.4 is not uniformcompared to Diagram 9.2 and

The resultant force acting on theis downward while the

resultant force acting on the right/ opposite to each

Instrument which uses thesame principle is electrical

has 2forces acting on the oppositeside caused by the counterreact between a currentcarrying conductor in a

/ diagram

(c)(i)

The shape of the magnet iscylindrical

It will produce uniformmagnetic field

(c)(ii)

The coil is placedsurrounding/fit toand it is attached to a cone

to increase the effectivthe counter react between themagnetic fields

(c)(iii)

The cone is made from a lightmaterial / paper

It can easily vibrate

(c)(iv)

Type of electrical supply isalternate current power supply

The audio signalcurrent.

(c)(v)

material used for the body othe loudspeaker is metal / wood

to ensure the loudspeaker isstrong

The shape of the magnet is

It will produce uniform

coil is placed/fit to the magnet

and it is attached to a coneto increase the effectiveness ofthe counter react between themagnetic fields .

The cone is made from a light/ paper

It can easily vibrate

e of electrical supply iscurrent power supply

The audio signal varies with the

material used for the body ofthe loudspeaker is metal / wood

re the loudspeaker is

FIZIKMOZAC 2010

36. Section B: SBP 08(a)(i)

The N-pole in Diagram 10.1 ismoved into the solenoid, the N-pole of the magnet in Diagram10.2 is moved out of the solenoid.

(ii) The galvanometer pointer inDiagram 10.1 deflects to the right,the galvanometer pointer inDiagram10.1deflects to the left.

(iii) -When N-pole is moved into thecoil, the top of the coil is a N-pole,and tends to repel themagnet-When the N-pole is pulled out ofthe coil, the top of the coil is a S-pole, and thus attracting thereceding N-pole.-The direction of the inducedelectromotive force acts in such away as to oppose the action whichproduces it.

(b)Lenz’s Law

(c) rotate the coil in clock wise

direction the coil cut across the

magnetic field current is induced in the coil the commuator change the

direction in the coil so that thedirection of current in externalcircuit I always the same.

(d)Modifications Reason

use thindiaphragm

Easy to vibrate

Use strongmaterial

Not easy to break

More numberof turns of coil

Increase the rate ofchange of magneticflux linkage /Themagnitude of theinduced current or isalso increased

Thickerdiameter ofwire of coil

reduce the resistanceof the coil

Using morepowerfulmagnet toincrease thestrength of themagnetic field

Increase the rate ofchange of magneticflux linkage //Themagnitude of theinduced current orinduced electromotiveforce is also increased

37. Section B: Melaka 09(a) Non uniform magnetic field(b) The angle of deflection of the

pointer in 10.2 is bigger The distance of the copper rod

in 10.2 is further Power supply in 10.2 is greater

then 10.1(c)(i)

The bigger the force thefurther the distance

(ii) The bigger the current thelarger the force

Current flows from Z to Y andfrom W to X in half cycle

Magnetic field form around thecopper strips

Current flows in oppositedirections in the half cycle

The copper strips movesoutwards// repel

(d)Modification Reason

use strongermagnet

stronger magneticfield / largerrotation

use curve magnets/ concave

produce radialmagnetic field / toget a linear scale

use cylindricalcore

to supply uniformmagnetic field

use soft iron core to concentrate themagnetic field

use linear scale the angle ofrotation is linear

FIZIKMOZAC 2010

38. Section B: kelantan 09(a) Process of producing electric

current by changing magneticfield.

(b)(i) North pole(b)(ii)

The more the bar magnets, thegreater the deflection of thegalvanometer

(c)(i)

The more the bar magnets, thestronger the magnetic fieldstrength

(c)(ii)

The stronger the magnetic fieldstrength, the greater thedeflection of the galvanometer.

(d)(i) Step down transformer(d)(ii)

When an alternating currentflows through the primarycoil, a changing magneticfield is produced.

The changing magnetic fieldwill is linkage through thesoft iron core to thesecondary coil

An alternating emf / current ofthe same frequency isinduced in the secondary coil

(e)Modifications Explanations

Use strongmagnet

Produce strongmagnetic field. Sohigh induced currentis produced.

Concave polesof magnets

Provide radialmagnetic field whichensures the cuttingof magnetic field isalways maximum.

Large number ofturns of the coil

Produce moreinduced current.

Larger area ofcoil

Produce moreinduced current

The speed ofrotation must behigh

Produce moreinduced current

39. Section B: Pahan 09(a) Work done to transfer 1 C of

charges from one point to another.(b) Electrical power is generated at

high current and low voltage Before transmission, current

passes through step uptransformer

During transmission, electricalpower is at low current and highvoltage to reduce power loss

At reception point, currentpasses through step downtransformer.

Electrical power is at lowvoltage and high current.

(c) Nonrenewable resources: Natural gas, petroleum Will be depleted Polute the environment

Renewable resources: Hidro, solar & wind Will not be depleted Does not pollute environment

(d)Modification explanation

Material:steel alloy

Strong and will notbreak easily

U-shaped steelalloy

Not too heavy

Trust and supportjoin

Can supportbigger weight

Large diametercable

Less resistance

Laminated wire To reduce eddycurrent

Made from lowdensity material

Cable is lighter

FIZIKMOZAC 2010

40. Section B: SBP 09(a)(i)

Electromagnet is a device inwhich magnetism is produced byan electric current// temporary magnet made by

winding a coil round a soft ironcore and magnetic field producewhen current flow.

(ii) Current flow in diagram 10.2 ismore than 10.1 // vice versa.

The amount of iron filingattracted by iron core inDiagram 10.2 is more than 10.1// vice versa.

The magnetic strength indiagram 10.2 is more than 10.1// vice versa.

Amount of iron filing attractedincrease when currentincrease

The magnetic field strengthincrease when currentincrease

(b) When too high current flow,magnetic field strengthbecome very strong / wireexpand

electromagnet pull the softiron armature / pulled to theright by spring P.

release the catch, contactseparate and current does notflow

When reset button is pressed,spring Q pulls the soft ironarmature back to its originalposition

(c)(i)

When the coil rotates the coilcut across the magnetic fieldlines

Induced current flow in thecoil.

The current maximum whenthe coil cut the magnetic fieldat right angle // currentdecreased (become zero) whenthe coil move in parallel withmagnetic field lines

The direction of current flowdetermine by using Fleming’sright hand rule

After 90o the direction ofcurrent in the external circuitreversed/ diagram

(ii)Modification Explanation

Change sliprings withcommutator

To reversecontact withbrushes sothat thecurrent flow insame directionin externalcircuit

Use strongermagnet

To increasethe magneticfield strength

Use morenumber ofturn for thecoil/ Increasethe speed ofrotation

Increase therate of changeof magneticfield/increasethe inducedcurrent