Unit 20Electromagnetism andElectromagnetic Induction

1. The diagram shows two long straight parallelwiresX and Y carrying current in the same directioninto the paper

o-----1-----o

3. A small plane coil connected to a sensitivegalvanometer is placed between the poles of an

electromagnet.

Switch S was closed and then opened again.Which of the following observations is true?A The galvanometer shows no defection as long

as the switch remains closed.

B The galvanometer shows brief defection inthe same direction on closing and opening theswitch S

C The galvanometer shows brief deflection inone direction on closing and in the oppositedirection when opening switch S.

D The galvanometer shows no deflection at allsince there is no relative movement of the coilwith respect to the electromagnet. ( )

4. The diagram below shows a circuit with a wireconnected to a battery through the switch S. Thecompasses X ar.d Z are placed above the wire andthe compass Y is placed below the wire.

Sx

P

What is the direction of the resultant magnetic fieldat P, the centre of the line joining both wires?

A direction ofresultant magnetic field

o -oBX

o-----direction ol

resultant magnetic field

C XPYO-----]+--O

direction ofresultant magnetic field

D No resultant magnetic field

2. Two long insulated wires carrying equal currents

are placed perpendicular to each other as shown.

.P Q.

.s R.

The points R Q" R and S are all at equal distances

from the wires. At which point(s) is/are theresulting magnetic field out of the paper?

A Ponly B QonlyC PandQ D Rands ( )

S

When S is closed,which of the followingdiagrams correctly shows the orientations of thecompass needles?

X IP

P

1

X YZ

-l

()

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5. The diagram shows a cross-sectional view of a

simple d.c. motor. The circles represent the sidesof a rectangular coil which is placed between thepoles of a permanent magnet. The current in theleft hand side of the coil fows into the plane ofthe diagram; the current in the right hand side ofthe coil flows out of the plane of the diagram.

What is the direction of the force experienced byeach side ofthe coil?

Left Hand Side Right Hand SideA Towards N Towards S

B Towards N UpC Up DownD Down Up

()

6. A metal rod is pulled to the right with a velocityz through a magnetic field as shown.

xxmagnetic field acting

perpendicularly into paper

xxx

x

x

x xx

Which of the following statements is true?A The induced current flows from Qto P

because P is at a higher potential.B The induced current flows from P to Q

because P is at a higher potential.C The induced current fows from Qto P

because Q*is at a higher potential.D The induced current flows from P to e

because Q*is at a higher potential. ( )

7. A free-moving wire is placed in a magnetic fieldas shown. A current flows from Q_to P. In whichdirection will the wire move?

S

A

8. Which diagram below shows the correct directionin which a current-carrying wire will move whenplaced in a magnetic field?

Ao Os

cC)

9. Two long wires AB and CD are connected tobatteries as shown below. In which directions willthe wires move?

WireAB

BA

CDC

N(

D

P

left right

oo

P

B

D

A

C

x

x

x

x

X

x

X

x

x

x

WiretJ

J

t

ABCD

J

J

II

CD

()

Sl

Dor--}

()

l4t

()

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10. The diagram below shows an electron, a, locatedin a magnetic field.

+

N

There is no magnetic force on the electron whenit moves

A towards the right side of the page

B towards the top of the page

C into the page

D out ofthe page

11. The diagram below shows the circular clockrvisepath of a charged particle in a field. The directionofthe field is out ofthe paper.

o

What will be the direction of the deflection, if any,

as the beam passes through the magnetic field?A Towards the top of the pageB Towards the bottom of the page

C Out of the paperD No deflection ( )

13. Two parallel wires carrying equal currentsexperience forces due to the mutual magneticeffects of the current. Which of the followingshows the correct directions for the forces actingon both the wires when they are placed near each

other?

A @++-@ B O+<€

C O+<re D <-€ O+()

1,4. In the diagram below, L and M are two looselyhung wires (one centimetre apart) connected toa battery through the switch S and immersed inmercury.

S

()

oo

o

o

O

a

o

o

o

a

o

O

o

oaa

o o

o

o

o

o

a

O

\raI

+

h

o O o o7\

ol

o o o a

at

tI

electron - .beam x+

x

L M

o

o a o

Ignoring the effect ofgravity,which of the followingcorrectly describes a possible state ofcharge oftheparticle and the nature ofthe field?

charge fieldA negative magneticB positive electricC negative electricD positive magnetic ( )

L2. the diagram below shows a beam of electrons

about to enter a magnetic field. The direction ofthe field is into the page.

xxxxxx

mercury

When S is closed,

A both L and M move to the rightB both L and M move to the leftC L and M will attract to each otherD L and M will repel each other (

15. A light metal rod is moved to the right on twoconducting rails as shown in the given diagram.Which of the following statements is correct?

xxx

X X X X Xmagneticfield

X X X X X intopage

xxxxx

magnetic x x xfieldinto page x

x

A P is at a higher potential and current flows

from P to Qthrough the rod.

B P is at a higher potential and current flowsfrom Qto P through the rod.

x

x

x

x

o

x

x

x

x

x

x

x

x

x

x

x

x

x

)

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C Qis at a higher potential and current flowsfrom P to Qthrough the rod.

D Qis at a higher potential and current flowsfrom Qto P through the rod. ( )

18. At the moment when the magnet is entering andleaving the coil, the polarity of the two ends ofthe coil PQis

1,6. Under the influence of the magnetic field in thediagram below; the stream of electrons is

-.stream of electrons

A deflected towards the north pole of the magnetB deflected towards the south pole ofthe magnetC deflected into the pianeD deflected out ofthe plane ofthe paper ( )

17. A student knows that 2 wires, P and Q are

carrying a 2 A current and a 1 A current buthe does not know which wire is carrying whichcurrent. He arranges 3 magnetic compasses, J, Kand L between the wires P and Qsuch that thecompass marked K is at the mid-point betweenthe two wires. (See plan view below)

K

What is the direction of the currents in P and Qand which wire carries more current?

Current direction Wire withinPandQ 2Acurrent

A both same direction PB both same direction QC different direction PD different direction a_ ( )

19. A straight wire connected to a galvanometer is

placed between the poles of a magnet.

galvanometer

Which change will cause a current in thegalvanometer?A Moving the wire in direction 1

B Moving the wire direction 2C Moving the magnet in direction 2D Moving the magnet in direction 3

IPN

S

o

Polarityof P(magnet entering

the coil)ANBNCSDS

Polarityof Q(magnetleaving

the coil)NS

NS

()

LJoo

P

o

2

+ t

t

-

m

1t

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20. The circle in the diagram outlines the point wherea beam of electrons moving "into the paper"enters a magnetic field. What will happen to theparticles?

N o

A Deflect to the leftB Deflect to the rightC Deflect upwardsD Deflect downwards

21. When a magnet was moved into the coil of wireshown in the diagram, there was a small readingon the sensitive meter.

N S

Which change would increase the size of thereading?A Moving the magnet fasterB Pulling the magnet outC Unwinding some of the turns ofwireD Starting with the magnet further away

(

22. A compass is placed at point X on the cardboard 25as shown in the diagram. The north pole of thecompass needle will point towards A, B, C or D?

23. A straight wire is placed between the poles ofa magnet. How should the wire be moved toproduce the greatest induced current in the wire?

wire

A Downwards and quicklyB Upwards and slowlyC Towards the magnet's poles and quicklyD Towards the magnet's poles and slowly

()

24. the diagram shows a brass rod supported on twocopper rails which are connected to a battery.The north pole of a magnet is placed as shownbeneath the rails. In which of the directions A, B,C, D does the brass rod experience a force?

brass rod

SN

\BC

rails

\

()

The figure below shows two iron rods suspendedside by side inside a coil by two elastic cords.When the circuit is closed at K, what will happento the rods?

elastic cords

iron rods

coil

A The rods repel each other.B The rods attract each other.C The rods move upwards.D The rods move downwards.

)

()

S

()

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26. Two long parallel wires PQand RS are connectedto batteries as shown in the diagram. PQcanmove freely in any direction but RS is fixed.

PRfree tomove fixed

OS

When both the switches are closed, what happensto wire PQ!A PQmoves towards RS.

B PQmoves away from RS.

C PQmoves in a direction into the plane ofthe paper.

D PQmoves in a direction out of the plane ofthe paper. ( )

27. Which of the following correctly shows themagnetic field produced by an electric current ina straight wire?

A B

+++

29. Jamie holds a wire between two strong magnets

as shown in the diagram. The current in the wireis 2 A. There is an upward force on the wire.

upward force

wtre

N

2A

When Jamie increases the current to 4 A, theupward force willA increase B decrease

C stay the same D reverse ( )

30. The diagram below shows a uniform magneticfield. A metal bar PQ-is swinging back and forthacross it as shown. The motion produced duringone complete to-and-fro oscillation started fromthe position shown.

uniformmagneticfield

Which of the following is correct?

A A current fows from P to Qthen Qto P.

B A current flows from Qto P then P to QC An alternating e.m.f in the direction PQthen

qP.D An alternating e.m.f in the direction QP

then PQ ( )

pushedinto the

coilleftleft

rightright

ABCD

pulled outofthe coil

to the rightleft

rightleft

right

stationary

no deflectionno deflectionno deflectionno deflection

()\/

DC

pq ---I

)

lr

P,28. The diagram below represents an experiment to

demonstrate electromagnetic induction.

Which of the deflections observed in thegalvanometer is correct when the north pole ofthe magnet is

"o

t)))))l I

I

SN

t45

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31. A rectangular coil is placed within a magnetic 33

field as shown. Current flows along the sides PQqR, RS and SP of the coil as represented by thearrows.

direction ofmagnetic field

----+

The N-pole of a bar magnet is pushed into a

solenoid. An electromotive force is induced thatmoves the galvanometer needle to the left.

galvanometer

Ro

Which combination shows the directions offorces acting on the sides ofthe coil?

Pq qR RS SPA Upwards Inwards Downwards InwardsB Upwards No force Downwards No forceC Downwards No force Upwards No forceD Downwards Inwards Upwards Upwards

()

32. 'Ihe diagram shows a magnet moving into a

solenoid.

.............._ solenoid

Which of the following changes would cause theneedle to defect in the opposite direction?A Push the solenoid towards the magnetB Pull the south pole away from the solenoidC Move the magnet and the solenoid at the

same speed to the rightD Move the solenoid awayfrom the magnet and

keep the magnet stationary ( )

solenoid

Which action, using the same end of thesolenoid, will produce a deflection in the samedirection?A Pulling a N-pole out of the solenoidB Pushing a S-pole into the solenoidC Pulling the solenoid away from a N-poleD Pulling the solenoid away from a S-pole

()

34. Ahoizontal wire carries a current in the directionshown in the diagram below between themagnetic poles N and S of nvo magnets. What is

the direction ofthe force?

N

current

P S

trt oushS

A FromNtoSB FromStoNC In the direction ofthe currentD Vertically upward ()

35. The figure below shows a brass rod, between thepoles of a horseshoe magnet, resting on two barehorizontal wires.

When the switch is closed, a current flows throughthe rod. In which direction will the rod move?

()

ND

+

N

S

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36. Two identical solenoids S, and S, are suspendedcoaxially and symmetrically by four long thinwires so that they may swing freely as shown inthe diagram. When the switch K is closed, whathappens to the solenoids?

38. When the generator below is operating, choosethe correct graph from A-D corresponding to thevariation of voltage with time across the resistorR.

K

s2

BAA One turns in a clockwise direction, and the

other in an anticlocloarise direction.B They both turn in a clockwise direction.C The move away from each other.D They move towards each other. ( )

37. Two nails P and Qare placed inside a coil, as

shown in the diagram below. P is free to movebut Qis fixed. The coil is joined to a battery and aswitch.

coil

switch

When the switch is closed, PA shoots out ofthe coilB moves to and froC moves towards qD moves away from Q

voltage voltage

voltage

39. The diagram below shows part of a d.c motor.

N

@ current into paper

@ current out of paper

As seen from the front, the coil willA rotate clockwiseB rotate anti-cloclaariseC experience no forceD experience no torque (

timeDC

T_time time

S

()

ao

SN

()

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40. The diagram below shows three pairs of parallel

wires with currents in the directions shown.

Which forces do the pairs of wires experience?

XYZA Attraction None Repulsion

B Attraction Repulsion AttractionC None Attraction NoneD Repulsion Attraction Repulsion

()

41. The diagram below shows a generator with its coillying horizontally.

What type of generator is this and at whatposition of the coil will the generator producemaximum induced e.m.f,?

Type ofgenerator Coil positionA a.c. generator verticalB d.c. generator verticalC a.c. generator horizontalD d.c. generator horizontal

()

42. the diagram below represents a bar magnet

oscillating vertically on the end ofa spiral springand passing through the centre ofa short-circuitedcoil of wire.

magnet

Which of the following statements is NOT true?A An induced magnetic field is set up in the coil

which opposes the motion of the magnet.B An alternating current is set up in the coilwhile

the bar magnet is moving.C A direct current flows in the coil when the bar

magnet comes to rest.

D The frequency ofthe current is equal to thefrequency of the oscillating magnet. ( )

43. The diagrams below show the front view of thecoil of an a.c. generator. The coil is being rotatedabout an axis though O in a uniform magneticfield between the N and S poles of permanentmagnets.Which diagram A, B, C or D best describesthe position of the coil when the induced e.m.f.is betlveen zero and its maximum value and isincreasing?

A

zX

B

iI+Ei IaEiC D

iI +Ei i]s Ei)(

magnet magnet

tlll

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44. the diagram shows two parallelwires P and Qinthe plane of the paper. P is 6xed; Qis free to move.When the same current, 1, passes through eachwire in same direction, Qmoves

A away from P in the plane of the paperB downwards into the paperC towards P in the plane of the paperD upwards out ofthe paper

47. Coil P is connected to acentre-zero galvanometer.Coil Q, connected to a battery and a switch S,

is placed above coil P as shown in the diagrambelow.

o

S

Which of the following graphs best representsthe deflection of the galvanometer when S is

closed for a few seconds and then opened?

A deflection

V time

B deflection

time

C deflection

P

o

P

Pr-)Xt\----+Jv tz uniform

+ magneticfietd

----+A charged particle at point P in a uniform magneticfield will not experience a magnetic force whenmovrngA into the plane of the paperB in the direction ofXC in the direction of YD in the directiotofZ ()

46. the diagram below shows an iron rod heldbetween the two magnets.

iron rod

tS

If the magnets move upwards, which of thestatements is/are true?I The current flows into the paper.II The current flows out of the paper.III The currents flows sidewards.

A I onlyB II onlyC I and III onlyD II andIII only (

48. Which of the following will NOT affect themagnitude ofthe induced e.m.f. in electromagneticinduction?A The speed with which a bar magnet is

thrown into a coilB The resistance of the coil cutting a magnetic

fie1d

C The frequency ofthe rotating coil in a

magnetic fieldD The strength of the bar magnet being thrown

into a coil()

D deflection

timet\7tN

I

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49. A rod is pulled to the right with velocity z througha magnetic field as shown.

xxx+Vxx x

x

x

xxxx

Which of the following statements is/are correct?I Qir at a higher potential than P.

II A current flows from Qto P in a rod if a wireis connected between P and Q

III The induced e.m.f. increases when thevelocity increases.

A II only B I and III onlyC II andIII only D I,II andIII ( )

50. In figure 1, the galvanometer deflects to the rightwith a reading of 10 mA. The south pole of the

same magnet is now pushed towards the coilfrom the other side at a slower rate as shown infigrre 2.

coil

+direction of motion

figure I

-

direction of motion

The direction of the galvanometer will be

A less than 10 mA to the rightB less than 10 mA to the leftC more than 10 mA to the leftD more than 10 mA to the right ( )

51. The diagram shows a long wire carrying a currentfrom the left to the right.

.p

.Q

.R

Which of the following statement(s) is/are true?I The direction of the magnetic field at P is

into the paper.

II The directions of the magnetic field at QandR are into the paper.

III The magnetic field at P is stronger than atR.

A II onlyB I and III onlyC II and III onlyD I, II and III

52. A flat piece of copper plate is allowed to swingbetween the poles of a powerful magnet.

copper plate

The reason why it quickly comes to rest is thatA the copper plate becomes an induced magnet.B an induced current fows in the copper plate

which produces a magnetic field which tendsto opposes the motion.

C the magnetic force around the copper plateopposes its motion.

D the kinetic energy ofthe copper plate ischanged to thermal energ'y due to frictionwith the magnetic field. ( )

53. Wire X is in a magnetic field and carries an

electric current.

wire

from d.c. supply

Which one of the following changes will doublethe catapult force on wire X?A The diameter of wire X is halved.

B The strength of the magnetic field is halved.

C The strength of the magnetic field is doubled.D An alternating current is used instead of a

direct current. ( )

xxxP

xxxxxxxxxxxxxxx

o

coil

N S

t

NS

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