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11. MAGNETIC EFFECTS OF ELECTRIC CURRENT

1) A Current carrying wire produces in its neighbourhood

A) zero field B) electric field only C) magnetic field only D) electric and magnetic fields

2) The magnetic induction in air at point 1 cm away from a long wire that carries a

current of 1 A, will be A) 1 10-5 T B) 2 10-5 T C) 3 10-5 T D) 4 10-5 T

3) A long straight wire carries an electric current of 2 A. The magnetic induction at a

perpendicular distance of 5 m from the wire is ( )104 170 Hm

A) 4 10-8 T B) 8 10-8 T C) 12 10-8 T D) 16 10-8 T

4) The magnetic field due to very long wire carrying current varies according to

A) square of the distance from the wire B) inverse of the distance from the wire C) square root of the distance from wire D) linearly as the distance from wire

5) What should be the current in a circular coil of radius 5 cm to annul

BH = 5 10-5 T at the center? A) 0.4 A B) 4 A C) 40 A D) 1 A

6) The magnetic field in a circular loop of diameter 0.1 m carrying a current of 1 A

is A) 3.8 10-5 B) 4.4 10-5 C) 2.8 10-5 D) 1.25 10-5

7) The earths magnetic induction at a certain point is 7 10-5 weber/m2. This is to

be annulled by the magnetic induction at the center of a circular conducting loop. The required current is nearly

[ ]/104 70 meterampweber

A) 0.56 amp B) 5.6 amp C) 0.28 amp D) none of these.

8) A particle having charge 100 times that of an electron is revolving in a circular

path of radius 0.8 m with one rotation per second. Magnetic field produced at the centre of the circular path is A) 10-17 B) 10-11

C) 10-7 D) 10-3

9) A wire of length L is bent to form a ring of single loop and current is flown

through it. The magnetic field at its centre is B. If the same wire is bent to form 2 loops and same current is flowing, the new B at its centre will be A) 2B B) B C) 4B D) B/2

10) In a coil of 0.1 m radius and 100 turns, 0.1 amp current is passed. What will be

the magnetic field at the centre of the coil A) 2 10-1 T B) 4.31 10-2 T C) 6.28 10-2 T D) 9.81 10-4 T

11) The magnetic field due to a current carrying circular loop of radius 3 cm at a point

on the axis at a distance of 4 cm from the centre is 54 T. what will be its value at the centre of the loop? A) 250 T B) 75 T C) 125 T D) 150 T

12) A circular coil of radius R carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from the center of the coil such that r >> R, varies as A) 1/r B) 1/r3/2 C) 1/r2 D) 1/r3

13) A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be A) n B B) 2 n2B C) 2nB D) n2 B

14) In hydrogen atom, the electron is making 6.6 1015 rev./sec around the nucleus in

an orbit of radius 0.528 .The magnetic moment (Am2) will be A) 1 10-15 B) 1 10-10 C) 1 10-23 D) 1 10-27

15) A magnetic needle lying parallel to a magnetic field requires W units of work to

turn it, through 600. The torque needed to maintain the needle in this position will be A) W3 B) W C) 23W D) 2 W

16) If number of turns, area and current through a coil is given by n, A and i

respectively then its magnetic moment will be A) ni A B) n2 iA C) ni A2 D) ni/ A

17) The work done in rotating a magnet of magnetic moment 2 Am2 in a magnetic

field of 5 10-3 T form the direction along the magnetic field to opposite direction to the magnetic field, is A) Zero B) 10-2J C) 10-2 J D) 10 J

18) A magnet of magnetic moment 2JT-1 is aligned in the direction of magnetic field of 0.1.T. What is the net work done to bring the magnet normal to the magnetic field? A) 0.1J B) 0.2J C) 10-2 D) 2J

19) A bar magnet is equivalent to

A) toroid carrying current B) straight conductor carrying current C) solenoid carrying current D) circular coil carrying current

20) Two straight horizontal parallel wires are carrying the same current in the same

direction, d is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires A) at a distance d/2 from any of the wires B) at a distance d/2 from any of the wires in the horizontal plane C) anywhere on the circumference of a vertical circle of a radius d and centre

half way between the wires, D) at points halfway between the wires in the horizontal plane.

21) A beam of electrons at rest is accelerated by a potential V. This beam

experiences a force F in a uniform magnetic field. The accelerating potential is changed to V and the force experienced by the electrons in the same magnetic field is 2F. The ratio V/V is A) 1 B) 2 C) D)

22) Two infinitely long wires carry currents in opposite directions. Then the field at

a point P lying midway between them is A) twice the field due to each wire alone B) half of the field due to each wire alone C) square of the field due to each wire alone D) zero

23) A wire of given length is first bent in one loop and the next time it is bent in

three loops. If the same current is passed in both the cases, the ratio of the magnetic field induction at their centres will be A) 1:4 B) 1:9 C) 9:1 D) 1:3

24) A proton (charge + e coul) enters a magnetic field of strength B (Tesla) with speed v, parallel to the direction of magnetic lines of force. The force on the proton is A) evB B) zero C) D) evB/2

25) A uniform electric field and a uniform magnetic field are produced, pointed in

the same direction. An electron is projected with its velocity pointed in the same direction A) the electron will turn to its left B) the electron will turn to its right C) the electron velocity will increase in magnitude D) the electron velocity will decrease in magnitude

26) A proton moving in a perpendicular magnetic field B possesses energy E. If the

magnetic field increases to 4B and the particle is constrained to move in the path of same radius the kinetic energy will A) increase 4 times B) increase 16 times C) reduce to half D) remains unchanged

27) The magnetic field of short magnet at a distance 1 m on the axial line is

1 oersted. At a distance of 2 m on the same line, the intensity in oersted is A) 0.5 B) 0.25 C) 0.125 D) 0.75

28) A long vertical wire in which a current is flowing produces a neutral point with

the earths magnetic field at a distance of 5 cms from the wire. If the horizontal component of the earths magnetic induction is 0.18 gauss, then the current in the wire, is A) 45 ampere B) 4.5 ampere C) 0.9 ampere D) 0.036 ampere

29) A charge q moves with a velocity

v in a magnetic field of induction B. If is

the angle between

v and

B , then the Lorentz force is minimum when A) = 0 B) = 300 C) = 900 D) = 1200

30) A long horizontally fixed wire carries a current of 100 amperes. Directly above

and parallel to it is a fine wire that carries a current of 20 ampere and weighs 0.04 newton per meter. The distance between the two wires for which the upper wire is just supported by magnetic repulsion is A) 10-2 decimetre B) 10-3 millimetre C) 10-2 metre D) 10-2 centimetre

31) Electron and proton of equal K.E. enter a uniform magnetic field normal to the

lines of force. If the radii of curvature of circular paths be r a and r p respectively, then A) ra/rp = 1/1

B) ra/rp = mp/ma

C) ra/rp = ap mm /

D) ra/rp = pa mm /

32) The electrons in the beam of a television tube have an energy of 12 KeV. The

tube is oriented so that the electrons move horizontally from south to north. The vertical component of earths magnetic field points down and has B = 5.5 10-5 weber / m2. In what direction will the beam deflect ? A) north B) south C) east D) west

33) A helium nucleus makes a full rotation in a circle of radius 0.8 metre in two

seconds. The value of the magnetic field B at the centre of the circle will be

A) 0

1910

B) 10-19 0

C) 2 10-19 0

D) 0

19102

34) Two thin long parallel wires separated by a distance b are carrying a current i ampere each. The magnitude of the force per unit length exerted by one wire on the other is

A) 22

0

bi

B) bi

2

20

C) bi

2

0

D) 22

0

2 bi

35) A solenoid of 1.5 metre length and 0.4 cm diameter possesses 10 turns per cm. A

current of 5 ampere is flowing through it. The magnetic induction at a point on the axis inside the solenoid is A) 2 10-3 tesla B) 2 10-5 tesla C) 2 10-2 gauss D) 2 10-5 gauss

36) A uniform magnetic field acts at right angles to the direction of motion of

electrons. As a result, the electrons move in a circular path of radius 2 cm. If the speed of the electron is doubled the radius of the circular path will be A) 2.0 cm B) 0.5 cm C) 4.0 cm D) 1.0 cm

37) If a long copper rod carries a direct current, the magnetic field associated with

the current will be A) only inside the rod B) only outside the rod C) both inside and outside the rod D) neither inside nor outside the rod.

38) A wire of length L m carrying a current i ampere is bent in the form of a circle.

The magnitude of magnetic moment is

A) 4

2iL

B) 2

2iL

C) 42 L2i D) L2i

39) The strength of the magnetic field at a point distance r near a long straight current carrying wire is B. The field at a distance r/2 will be A) B/2 B) B/4 C) 2B D) 4B

40) The number of turns and radius of cross section of the coil of a tangent

galvanometer are doubled, its reduction factor is K. The new reduction factor K will be A) K B) 2K C) 4K D) K/4

41) A long wire carries a current of 20 A along the axis of a solenoid. The field due to

the solenoid is 4 mT. The resultant field at a point 3 mm from the solenoid axis is A) 1.33 mT B) 4.2 mT C) 5.33 mT D) 2.87 mT

42) P, Q and R are long parallel straight wires in air, carrying currents as shown

below. What is the direction of the resultant force on Q ?

A) to the left B) to the right C) the same as that of current in Q D) perpendicular to this page

43) Suppose that a proton traveling in vacuum with velocity v1 at right angles to a

uniform magnetic field experiences twice the force that an particle

experience when it is traveling along the same path with velocity v2. The ratio 2

1

vv

is A) 0.5 B) 1 C) 2 D) 4

44) A particle carrying a charge equal to 100 times the charge of the electrons is rotating per second in a circular path of radius 0.8 m. The value of magnetic field produced at the centre will be ( = permeability for vacuum)

A)

710

B) 10-6 C) 10-17 D) 10-7

45) In hydrogen atom the electron moves in an orbit of radius 0.5 making 1016

revolutions per second. The magnetic moment associated with the orbital motion of the electron in Am2 is A) 1.25 10-18 B) 1.25 10-23 C) 25 10-23 D) 25 10-38

46) In hydrogen atom, the electron is making 6.6 1015 rev/sec around the nucleus

of radius 0.53 . The magnetic field produced at the centre of the orbit is nearly A) 0.14 weber/m2 B) 1.4 weber/m2 C) 14 weber/m2 D) 140 weber/m2

47) The magnetic field at a distance r from a long wire carrying current i is 0.4

tesla . The magnetic field at a distance 2r is A) 0.2 telsa B) 0.8 telsa C) 0.1 telsa D) 1.6 telsa

48) A circular current carrying coil has a radius R. The distance from the centre of

the coil on the axis where the magnetic induction will be 1/8th of its value at the centre of the coil is A) R/ 3 B) R/ 3 C) 2R 3 D) R3/2

49) If the speed of the electrons is 5 105 ms-1. how long does it take one electron to

traverse 1m A) 1 106 sec B) 2 x 10-6 sec C) 2 105 sec D) 1 x 105 sec

50) What is the force on each single electron assuming that each electron

experiences the same force A) 7.5 10-11 N B) 8 10-13 N C) 7.25 10-15 N D) 2.5 10-17 N

51) A wire of length L carrying current i is placed perpendicular to the magnetic

induction B. The total force on the wire is A) iLB B) iB/L C) iL/B D) LB/i

52) A steel wire of length l has a magnetic moment M. It is then bent into a semi-

circular arc. The new magnetic moment is A) M B) 2M/ C) M / l D) M l

53) What is magnetic induction at point O, if the current carrying wire is in the shape

given in the figure?

A) ri

4

0

B) ri

4

0

12

C) ri

4

0

2.

D) ri

4

0

12

3

54) A wire is bent in the form of a circular arc with a straight portion AB. If the current in the wire is i, find magnetic induction at O.

A) ri

2

0 (tan )

B) ri

2

0 ( - )

C) ri

2

0 ( - + tan )

D) ri

2

0 ( - tan )

55) A long wire is bent into a circular loop and long straight wires on either side but

there being no contact at point P. If current i enters at Q and leaves at R, then what is magnetic induction at O.

A) ri

2

0

B) ri

20

C) ri

20

11

D) ri

20

11

56) The magnetic field at the centre of the circular coil carrying current of 4A is

A) 510

38 T

B) 4103

8 T

C) 5102 T D) 4102 T

57) An infinitely long straight conductor is bent into the shape as shown in fig. The magnetic induction at the centre of circular loop is

A) zero B)

C) ri

2

0 ( +1)

D) ri

2

0 ( -1)

58) In the fig given below magnetic induction at the point O is

A) rI

4

0

B) rI

40 +

rI

2

0

C) rI

40 +

rI

4

0

D) rI

40 -

rI

4

0

59) A wire of given length is first bent in one loop and then in three loops. If same

current is passed in both cases, the ratio of magnetic inductions at the centre will be A) 1 : 4 B) 1 : 9 C) 9 : 1 D) 1 : 3

60) The magnetic induction at centre O is

A) rI

4

0

B) rI

40

C) rI

20

D) r

I0

61) Two protons move parallel to each other with equal speeds 3 x 105 ms-1. The ratio of magnetic and electric force between them is A) 10-3 B) 10-6 C) 10-9 D) 1

62) Two long straight wires are connected by a circular section which has radius R. All the three segments lie in same plane and carry a current I. The magnetic induction at centre O of the circular segment is

A) RI

4

0

B) R

I

4.0

C) R

I0

D) RI

2

0

63) ABCD is a circular coil of non-insulated thin uniform conductor. Conductors pA and qC are very long straight parallel wires, tangential to the coil at points A and C. Find magnetic induction at centre of coil when a current of 5 A is passing thereby. Radius of coil is 10 cm

A) 0.5 10-5 T B) 10-5 T C) 2 10-5 T D) None of these

64) An ammeter has resistance R0 and range I. What resistance should be connected

in parallel to it with increase the range to nI

A) n

R0

B) 1

0

nR

C) 1

0

nR

D) None of these

65) A voltmeter has range V. What resistance should be connected in series with it to increase its range to nV. Initial resistance is R0 A) nR0 B) (n + 1) R0 C) (n - 1) R0

D) n

Ro

66) An electron is revolving around a proton in a circular orbit of diameter 0.1 nm. It

produces a magnetic field of 14 Wbm2 at the proton. What is angular speed of the electron? A) 1.4 1016 rad s-1 B) 4.4 1016 rad s-1 C) 6.4 1016 rad s-1 D) 8.8 1016 rad s-1

67) A magnetic dipole is placed in two magnetic fields B and B0. It is in equilibrium

making an angle with direction of field B, then

A) B = B0 B) B cos = B0 sin C) B sin = B0 cos D) B = B0 tan

68) What is magnetic field in the empty space enclosed by toroidal solenoid of radius R? A) Infinity

B) RI2

40

C) nI0 D) Zero

69) The ratio of magnetic induction on the axis of a straight long current carrying solenoid at a point on end to that at the centre of solenoid is A) 1 : 1 B) 1 : 2 C) 2 : 1 D) 2 : 1

70) A ring of radius r is uniformly charged with charge q. It is rotated with angular velocity , then magnetic moment developed by the ring is

A) 2

2qr

B) 22rq

C) 22rq

D) 2

2qr

71) If only 2% of the current is to pass through a galvanometer of resistance G, then

resistance of shunt will be

A) 50G

B) 49G

C) 50 G D) 49 G

72) An electron is shot into a liquid placed in a uniform magnetic field, in a plane perpendicular to magnetic field, then A) the trajectory of electron is circular B) trajectory is an inward winding spiral C) the kinetic energy of electron remains same D) its revolution frequency decreases.

73) A galvanometer having 30 divisions has a current sensitivity of 20 A/div. It has a resistance of 25 ohm. How will you convert it into an ammeter measuring upto 1 ampere. Find the shunt to be used A) 0.15 B) 0.015 C) 0.030 D) 0.30

74) A voltmeter has a range O-V with a series resistance of R ohm. With a series resistance of 2R, its range is O-V then A) V > 2V B) V = 2V C) V < 2V D) V > 2V

75) A very long wire carrying current I=10 A is bent at right angle at O, find the magnetic induction at the point P lying on perpendicular to the wire at the point O, at a distance of 35 cm.

A) 1 10-6 T B) 2 10-6 T C) 3 10-6 T D) 4 10-6 T

76) A solenoid has a mean diameter of 0.05 m and length 2m. It has four layers of 1000 turns each. What is flux density at its centre, when a current of 2.5 A flows through it A) 3.24 10-2 T B) 6.28 10-3 T C) 6.28 10-4 T D) 3.24 10-5 T

77) Two long parallel wires are carrying currents 12 A and 8 A in the same direction. The wires are 10 cms. Apart. Where a third parallel wire must be placed so as to experience no force?

A) 6 cm from P B) 3 cm from P C) 2 cm from P D) 1.5 cm from P

78) A proton, deuteron and -particle having same K.E. are moving in circular paths in a constant magnetic field applied to all. If p , d and a are radii of the paths of these particles then A) = p > d B) > d > p C) = d > p D) p = d = a

79) If an electron describes half a revolution in a circle of radius r, in a magnetic field B, the energy acquired by it is A) Zero B) 1/2 mv2

C) 41 mv2

D) r BeV

80) Fig shows three long straight conductors A, B and C having currents 3A, 1A and 2A respectively. The wire B is of length 0.5 m. It will experience the force

A) 10-5N from left to right B) 10-5N from right to left C) 5 10-6N from left to right D) 5 10-6N from right to left

81) A current I flows through a section of wire as shown in the figure. The magnetic

induction at the point P is

A)

B) 22

20 1

4 DCL

D

C) DI

4

0

D) LI

4

0

82) The magnetic field at the centre of current carrying conductor as shown in fig. is

A)

224

0

rI

B)

42

420

rI

C)

24

0

rI

D)

42

40

rI

83) The magnetic induction at point O distance r from the corner of an infinitely long wire carrying current I and bent at right angle is

A) I4

0

B) rI

0

C) rI

4

0

D) Zero

84) An electron is moving with velocity ji 33 in the magnetic field of intensity ki 32 T. The force acting on electron is A) 1.6 10-18N B) 2.25 10-18N C) 4.5 10-18N D) zero

85) A rectangular coil of size 3.0 4.0 cm and having 100 turns, is pivoted about the

Z-axis as shown in Fig.

The coil carries an electric current of 2.0 A and a magnetic field of 1.0 T is present along the Y-axis. Find the torque acting on the coil if the side in the X-Y plane makes an angle =370 with the X-axis. A) 0.28 N-m B) 0.14 N-m C) 0.37 N-m D) 0.47 N-m

86) A particle having a charge 20 C and mass 20 g moves along a circle of radius

5.0 cm under the action of a magnetic field B=1.0 T. When the particle is at a point P, a uniform electric field is switched on and it is found that the particle continues on the tangent through P with a uniform velocity. Find the electric field A) 0.5 V-m-1 B) 1.0 V-m-1 C) 5.0 V-m-1 D) None of these

87) In the Fig. X and Y are two long straight conductors each carrying a current of

2 A. The force on each conductor is F. When the current in each is changed to 1 A and reversed in direction, the force on each is now

A) F/4 and unchanged direction B) F/2 and reversed direction C) F/2 and unchanged direction D) F/4 and reversed direction

88) A charged particle enters a region of non-uniform field and eventually comes out

of it. As it emerges, its A) speed is greater as compared to the speed at entry point. B) Velocity remains unchanged C) Velocity may change but speed remains unchanged D) Speed cannot be estimated as data is insufficient.

89) A circular current carrying coil has a radius R. The distance from the centre of the

coil, on the axis where the magnetic induction will be 1/8th of its value at the centre of the coil, is A) R 3 B) R / 3

C) 3

2R

D) (2 / 3 ) R.

90) The magnetic induction at the centre O in the following figure is

A) rI

4

0

B) Zero

C) r

I

4)1(0

D) r

I

4)1(0

91) Through two parallel wires A and B, 10 A and 2 A of currents are passed

respectively in opposite directions. If the wire A is infinitely long and the length of the wire B is 2m, the force on the conductor B, which is situated at 10 cm distance from A, will be A) 8 10-5N B) 3 10-7N C) 4 10-5N D) d) 4 10-7N

92) A particle carrying a charge equal to 100 times the charge on an electron, is rotating at the rate of one rotation per second in a circular path of radius 0.8 m. The value of the magnetic field produced at the centre will be (0, permeability of free space) A) 10-7/ 0 Wb/m2 B) 10-17 0 Wb/m2 C) 10-6 0 Wb/m2 D) 10-7 0 Wb/m2

93) An electron of mass 0.90 x 10-30 kg. under the action of magnetic field moves in a

circle of radius 2.0 cm at a speed of 3.0 x 106 ms-1. If a proton of mass 1.8 x 10-27 kg were to move in a circle of the same radius in the same magnetic field, then its speed would be

A) 30 106 ms-1 B) 1.5 103 ms-1 C) 6 104 ms-1 D) unestimable from the above data

94) An electron is accelerated to a high speed down the axis of a cathode ray tube by

the application of a potential difference of V volts between the cathode and anode. The particle then passes through a uniform transverse magnetic field in which it experiences force F. If the potential difference between the anode and the cathode is increased to 2V, the electron will now experience a force A) F/ 2 B) F/2 C) 2 F D) 2F

95) The direction of the force experience by a charged particle moving with a velocity

in a uniform magnetic field B is A) Parallel to and perpendicular to B B) Parallel to B an perpendicular to C) Parallel to both and B D) Perpendicular to both and B

96) A length of wire carries a steady current. It is bent to from circular coil of one turn

only. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre caused by the same current is A) A half of its first value B) Unaltered C) A quarter of its first value D) Four times its first value

97) A conducting circular loop of radius r carries a constant current I. It is placed in

uniform magnetic field B such that B is perpendicular to the plane of the loop. The net magnetic force acting on the loop is A) I r B B) 2 r IB C) Zero D) r IB

98) If protons are shot perpendicular to a magnetic field A) Magnetic field will have no influence on the motion of protons B) Protons will continue to move in the same direction but will gain

momentum C) Protons will continue to move in the opposite directions but will gain

momentum D) They will bend in arc of a circle

99) A helium nucleus makes a full rotation in a circle of radius 0.8 metre in two seconds. The value of the magnetic field B at the centre of circle will be

A) 0

1910

B) 10-19 0

C) 2 10-19 0

D) 0

19102

100) The magnetic field midway between two parallel current carrying wires, carrying

currents i and 2i is B

. If the current in the wire with current i is switched off, the magnetic field will become

A) 3B

B) 2 B

C) 2B

D) 4B

101) P, Q and R are long parallel straight wires in air, carrying currents as shown in

Fig. What is the direction of the resultant force on Q?

A) To the left B) To the right C) Perpendicular to this page D) The same as that of the current in Q

102) Two thin long parallel wires separated by a distance b are carrying a current i amp. each. The magnitude of the force per unit length exerted by one wire on the other is

A) 2

20 b

i

B) bi

2

20

C) 20

2 bi

D) bi

2

0

103) If a long copper rod carries a direct current, the magnetic field associated with the

current will be A) inside the rod only B) outside the rod only C) both inside and outside the rod D) neither inside nor outside the rod

104) If a proton is projected in a direction perpendicular to a uniform magnetic field

with velocity and an electron is projected along the lines of force, what will happen to proton and electron? A) The electron will travel along a circle with constant speed and proton will

move along a straight line B) Proton will move in a circle with constant speed and there will be no effect

on the motion of electron C) There will not be any effect on the motion of electron and proton D) The electron and proton both will follow the path of parabola.

105) A proton (mass m and charge + e) and -particle (mass 4 m and charge + 2e) are

projected with the same kinetic energy at right angles to a uniform magnetic field. Which one of the following statements will be true? A) The particle will be bent in a circular path with smaller radius than

proton B) The radius of the path of -particle will be greater than that of proton. C) Radius of the paths of both the particles will be the same. D) Both will go through the magnetic field in the straight line.

106) A particle of mass m carrying charge q is accelerated by a p.d. V. It enters perpendicularly a region of uniform magnetic field B and executes circular arc of radius R. The specific charge (q/m) is

A) 222

RBV

B) BRV

2

C) R

VB2

D) BRmV

107) An irregular closed loop carrying current has such a shape that the entire loop

cannot lie in a single plane. If this loop is placed in a uniform magnetic field, the force acting on the loop A) must be zero B) can never be zero C) can be zero only for one particular direction of the magnetic field D) can not be ascertained.

108) A conducting loop carrying a current I is placed in a uniform magnetic field

pointing into the plane of paper as shown. The loop will have a tendency to

A) contract B) expand C) move towards +ve x-axis D) move towards ve x-axis.

109) A particle of charge -16 x 10-18 C moving with a velocity 10 ms-1 along the x-axis

enters a region where a magnetic field of magnitude B is along the y-axis and an electric field of magnitude 104 V/m is along negative z-axis. If the charged particle continues moving along x-axis, find magnitude of B A) 106 Wb/m2 B) 1016 Wb/m2 C) 10-3 Wb/m2 D) 103 Wb/m2

110) A particular of mass M and charge Q moving with velocity V describes a circular path of radius R when subjected to a uniform magnetic field (transverse) of induction B. The work done by the field when particle completes one full circle is A) Zero B) BQ.2R C) BQ. . 2 R

D) RR

MV2

2

111) A charge moving with velocity in X direction is subjected to a field of

magnetic induction in the negative X direction. As a result the charge will A) remain unaffected B) start moving in a circular path in Y-Z plane C) retard along X-axis D) move along a helical path around X-axis

112) A current loop of area 0.01 m2 and carrying a current of 10 amp. is held

perpendicular to a magnetic field of induction of 0.1 tesla. The torque (in Nm) acting on the loop is A) 0 B) 0.001 C) 0.01 D) 1.1

113) An electron having energy 10 eV is circulating in a path having magnetic field of

10-4 T. The speed of the electron will be A) 3.8 106 m/s B) 1.9 1012 m/s C) 3.8 1012 m/s D) 1.9 106 m/s

114) A particle having charge 100 times that of an electron is revolving in a circular

path of radius 0.8 m with one rotation per second. The magnetic field produced at the centre is: A) 10-17 0

B) 10-17/ 0 C) 10-16 0

D) 10-15 0

115) Two concentric coils of 10 turns each are situated in the same plane. Their radii are 20 and 40 cm and they carry respectively 0.2 and 0.3 ampere current in opposite directions. The magnetic field in Wb/m2 at the centre is

A) 032

B) 045

C) 041

D) 6

0

116) Two parallel conductors are carrying current i in the same direction. Force

experienced per unit length by each conductor (distance between the conductors is r) would be

A) Repulsion and ri

4

0

B) Repulsion and

ri 22

4

C) Attraction and ri

4

0

D) Attraction and

ri 22

4

117) A length of wire carries a steady current. It is bent first to form a circular plane

coil of one turn. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre caused by the same current is A) a quarter of its first value B) unaltered C) four times of its first value D) a half of its first value

118) A current carrying small loop behaves like a small magnet. If A be its area and M

its magnetic moment, the current in the loop will be A) M/A B) A/M C) MA D) A2M

119) If only 2% of the main current is to be passed through a galvanometer of resistance G then the resistance of the shunt will be A) G/50 B) G/49 C) 50G D) 49G

120) A straight thin conductor is bent as shown in adjoining figure. It carries a current i

ampere. The radius of circular arc is r meter, then the magnetic induction at the centre of semi-circular arc is

A) zero B)

C) ri

4

tesla

D) ri

4

tesla

121) If a particle, moving in a magnetic field, increases its velocity, then its radius of

the magnetic field circle will A) remain constant B) decrease C) increase D) either (b) or (c)

122) If a particle is moving in a uniform magnetic field, then A) its momentum changes but total energy remains the same B) both momentum and total energy remains the same C) its total energy changes but momentum remains same D) both momentum and total energy will change

123) A wire of length 0.5 metre and carrying a current of 0.2 A is placed in a uniform

magnetic field of induction 2 tesla. If the magnetic field is perpendicular to the length of the wire, then the force on the wire is A) 0.4 N B) 1.2 N C) 3.0 N D) 4.2 N

124) A galvanometer of resistance 25 is shunted by a 2.5 wire. The part of total

current that flows through the galvanometer is given by

A) 111

oII

B) 112

oII

C) 113

oII

D) 114

oII

125) The resistance of ideal voltmeter is

A) zero B) infinity C) 100 D) 500

126) A rectangular loop carrying a current I is situated near a long straight wire such

that the wire is parallel to the one of the sides of the loop and is in plane of the loop. If a steady current I is established in the wire as shown in fig. the loop will

A) rotate about an axis parallel to the wire B) move away from the wire or towards right C) move towards the wire D) remains stationary

127) The resistance of a galvanometer is 50 and the current required to give full

scale deflection is 100 A. In order to convert it into an ammeter for reading up to 10 A, it is necessary to put a resistance of A) 5 10-3 B) 5 10-4 C) 5 10-5 D) 5 10-2

128) A straight wire of diameter 0.5 mm carrying a current of 1 ampere is replaced by another wire of 1 mm diameter carrying the same current. The strength of the magnetic field far away is A) twice the earlier value B) one half of the earlier value C) one quarter of the earlier value D) same as the earlier value.

129) A direct current flows in a long straight conductor whose crossection has a form

of a thin half ring of radius R. The same current flows in opposite direction along a thin conductor placed on the axis of first conductor, then the magnetic interaction force between the conductors to a unit of their length is.

A) RI

2

20

B) RI

2

0

C) RI

20

D) R

I02

130) A thin circular loop carrying a current has a radius 100 mm and magnetic

induction at its centre is 6.0 T. Then magnetic moment of the loop is A) 15 mA-m2 B) 30 mA-m2 C) 45 mA-m2 D) 60 mA-m2

131) Two tangent galvanometers have radii 7.5 cm and 10 cm, number of turns are 15 and 10 and resistances are 8 and 12 . They are joined in parallel in the circuit. If deflection in one is 60o, the deflection in the second galvanometer is

A) 45o B) 30o C) 40o D) 35o

132) A tangent galvanometer is most sensitive when the deflection is around

A) 0o B) 30o C) 45o D) 90o

133) A tangent galvanometer has a coil of 50 turns and a radius of 20.0 cm. The horizontal component of earths magnetic field is 3 x 10-5 T. The current which gives the deflection of 45o is

A) A51

B) A53

C) A41

D) A43

134) A horizontal overhead power line carries a current of 90 A in the east to west

direction. What is the magnitude and direction of the magnetic field due to the current 1.5 m below the line? A) 0.6 10-5 T towards north B) 0.6 10-5 T towards south C) 1.2 10-5 T towards north D) 1.2 10-5 T towards south

135) A horizontal circular coil has 50 turns and a mean radius of 3.14 cm. It carries a current of 3.0 A. The current is clockwise. What is the magnitude and direction of the magnetic field at the centre of the coil? A) 3.0 10-4 T perpendicular to the place of the coil pointing down wards B) 3.0 10-4 T perpendicular to the plane of the coil pointing upwards C) 3.0 10-5 T parallel to the plane of the coil pointing to the right D) 3.0 10-5 T parallel to the plane of the coil pointing to the left

136) The magnetic field on the axis of a current carrying circular loop of radius r at a

distance x >> r from the centre of the loop is B. If the radius of the loop is doubled, keeping the current unchanged , the magnetic field at x >> r would be

A) 4B

B) 2B

C) 2B D) 4B

137) Two concentric circular coils X and Y of radii 16 cm and 10 cm respectively lie in the same vertical plane containing the north south direction. Coil X has 20 turns and carries a current of 16 A; coil Y has 25 turns and carries a current of 18 A. The sense of the current in X is anticlockwise, and in Y clockwise, for an observer looking at the coils facing the west. What is the magnitude and direction of the magnetic field at their common centre due to coil X alone? A) 2 10-4 T towards east B) 2 10-4 T towards west C) 4 10-4 T towards east D) 4 10-4 T towards west

138) In Q. 137 what is the magnitude and direction of the magnetic field at their

common centre due to coil Y alone? A) 9 10-4 T towards east B) 9 10-4 T towards west C) 4 10-4 T towards east D) 4 10-4 T towards west

139) In Q. 137, what is the magnitude and direction of the net magnetic field at their common centre due to both the coils? A) 5 10-4 T towards west B) 5 10-4 T towards east C) 13 10-4 T towards west D) 13 10-4 T towards east

140) A straight wire carrying a current of 10 A is bent into a semi-circular arc of radius cm as shown in the figure. What is the magnitude and direction of the magnetic field at centre O of the arc?

A) 10-4 T normal to the plane of the arc and directed into the page B) 10-4 T normal to the plane of the arc and directed outside the page C) 2 10-4 T parallel to the plane of the arc and directed to the left. D) 2 10-4 T parallel to the plane of the arc and directed to the right.

141) A straight wire carrying a current of 10 A is bent into a semicircular arc of radius cm as shown in the figure. What is the magnitude and direction of the magnetic field at the centre O of the arc?

A) 10-4 T normal to the plane of the arc and directed into the page B) 10-4 T normal to the plane of the arc and directed outside the page C) 2 10-4 T parallel to the plane of the arc and directed to the left D) 2 10-4 T parallel to the plane of the arc and directed to the right

142) A wire of length L carrying a current I is bent into a circle. The magnitude of the

magnetic field at the centre of the circle is

A) L

I0

B) LI

20

C) L

I02

D) LI

2

0

143) A part of a long wire carrying current I is bent into a circle of radius r as shown

in the figure. The net magnetic field at the centre O of the circular loop is

A) rI

40

B) rI

20

C) 12

0

rI

D) 12

0

rI

144) A wire is bent into a circular loop of radius R and carries a current I. The magnetic field at the centre of the loop is B. The same wire is now bent into a double loop. If both loops carry the same current I in the same direction, the magnetic field at the centre of the double loop will be A) zero B) 2 B C) 4 B D) 8 B

145) In Q. 144, if the currents I in the two loops are in opposite directions, the magnetic field at the centre of the double loop will be A) zero B) B

C) 4B

D) 4 B

146) The wire loop PQRSP formed by joining two semi circular wires to radii R1 and R2 carries a current I as shown in the figure. The magnitude of the magnetic induction at centre C is

A)

21

0 114 RR

I

B)

21

0 114 RR

I

C)

21

0 112 RR

I

D)

21

0 112 RR

I

147) The magnetic field at the centre of a circular coil of radius r and carrying a current I is B. What is the magnetic field at a distance 3x r from the centre, on the axis of the coil? A) B B) 2 B C) 4 B D) 8 B

148) If an electron and a proton are projected at right angles to a uniform magnetic field with the same kinetic energy, A) The electron trajectory will be less curved then the proton trajectory B) The proton trajectory will be less curved then the electron trajectory C) Both trajectories will be equally curved D) Both particles move in straight lines

149) If an electron and a proton are projected at right angles to a uniform magnetic

field with the same linear momentum, A) the electron trajectory will be less curved than the proton trajectory B) the proton trajectory will be less curved then the electron trajectory C) both trajectories will be equally curved D) both particles move in straight lines.

150) Two identical coils carry equal currents and have a common centre, but their

planes are at right angles to each other. What is the magnitude of the resultant magnetic field at the centre if the field due to one coil alone is B? A) zero B) 2/B C) 2 B D) 2 B

151) When a charged particle moves perpendicular to a uniform magnetic field, its A) energy and momentum both change B) energy changes but momentum remains unchanged C) momentum changes but energy remains unchanged D) energy and momentum both do not change

152) In the region around a charge at rest, there is A) electric field only B) magnetic field only C) neither electric nor magnetic field D) electric as well as magnetic field

153) In the region around a moving charge, there is A) electric field only B) magnetic field only C) neither electric nor magnetic field D) electric as well as magnetic field

154) An electron is accelerated to a high speed down the axis of a cathode ray tube by

the application of a potential difference of V volts between the cathode and the anode. The particle then passes through a uniform transverse magnetic field in which it experiences a force F. If the potential difference between the anode and the cathode is increased to 2 V, the electron will now experience a force A) 2/F B) 2/F C) 2 F D) 2 F

155) A magnetic needled is kept in a non-uniform magnetic field. It experiences

A) a force as well as a torque B) a force but no torque C) a torque but no force D) neither a force nor a torque

156) A conducting circular loop of radius r carries a constant i. It is placed in a uniform

magnetic field B such that B is perpendicular to the plane of the loop. The magnetic force acting on the loop is A) I r B B) 2 i r B C) zero D) i r B

157) A rectangular loop carrying a current i is situated near a long straight wire such that the wire is parallel to one of the sides of the loop. If a steady current I is established in the wire, as shown in the figure, the loop will

A) rotate about an axis parallel to the wire B) move away from the wire C) move towards the wire D) remain stationary

158) Two long parallel wires separated by a distance R have equal currents I flowing in each. The magnetic field of one exerts a force F on the other. The distance R is increased to 2R and the current in each wire is reduced from I to I/2. What is the force between them now? A) 4 F B) F C) F / 4 D) F / 8

159) In the hydrogen atom the electron moves around the proton with a speed of 2.0 106 ms-1 in a circular orbit of radius 5.0 10-11 m. What is the equivalent dipole moment? A) 2 10-24 Am2 B) 4 10-24 Am2 C) 8 10-24 Am2 D) 16 10-24 Am2

160) In Q.159, what is the strength of the magnetic field at the site of the proton (i.e. at the centre of the orbit)? A) 12.8 T B) 6.4 T C) 3.2 T D) 1.6 T

161) In a hydrogen atom, an electron of mass m and charge e is in an orbit of radius r

making n revolutions per second. If the mass of the hydrogen nucleus is M, the magnetic moment associated with the orbital motion of the electron is

A) M

mner 2

B) m

Mner 2

C) mMmner

2

D) n e r 2

162) A wire of length l metres carrying a current I amperes is bent in the form of a circle. The magnitude of the magnetic moment is

A) 2

2I

B) 4

2I

C) 2

2 I

D) 4

2 I

163) A rectangular coil of 50 turns carries a current of 2.0 A and is placed in a magnetic field B of 0.25 T, as shown in the figure. What is the magnitude of torque acting on the coil?

A) 0.1 Nm B) 0.2 Nm C) 0.3 Nm D) 0.4 Nm

164) Two circular current carrying coils of radii 3 cm and 6 cm are each equivalent to a magnetic dipole having equal magnetic moments. The currents through the coils are in the ratio of A) 2 :1 B) 2 : 1 C) 2 2 : 1 D) 4 : 1

165) An electron of charge e moves in a circular orbit of radius r around the nucleus at a frequency v. The magnetic moment associated with the orbital motion of the electron is A) v e r2

B) er 2

C) 2rve

D) vve

166) An electron of charge e moves in a circular orbit of radius r around a nucleus. The magnetic field due to orbital motion of the electron at the site of the nucleus is B. The angular velocity of the electron is

A) reB

4

2 0

B) reB

0

C) e

rB0

4

D) e

rB0

2

167) The frequency of the charged particle circulating at right angles to the uniform

magnetic field does not depend upon the A) speed of the particle B) mass of the particle C) charge of the particle D) magnetic field

168) Three long, straight and parallel wires C, D and G carrying currents are arranged

as shown in the figure. The force experienced by a 25 cm length of wire C is

A) 0.4 N B) 0.04 N C) 4 10-3 N D) 4 10-4 N

169) An electron of mass m and charge e is accelerated by a potential difference V. It then enters a uniform magnetic field B applied perpendicular to its path. The radius of the circular path of the electron is

A) 2/1

2

2

eBmVr

B) 2/1

2

2

BmeVr

C) 2/1

2

2

eVmBr

D) 2/122

emVBr

170) The wire shown in the figure carries a current of 40 A. If r = 3.14 cm, the

magnetic field at point P will be

A) 1.6 10-3 T B) 3.2 10-3 T C) 4.8 10-3 T D) 6.4 10-3 T

171) A current I flows along the length of an infinitely long, straight, thin walled pipe. Then A) the magnetic field at all points inside the pipe is the same but not zero B) the magnetic field at any point inside the pipe is zero C) the magnetic field is zero only on the axis of the pipe D) the magnetic field is different at different points inside the pipe

172) A power line lies along the east-west direction and carries a current of 10 A. The

force per meter due to the earths magnetic field of 10-4 T is A) 10-5 N B) 10-4 N C) 10-3 N D) 10-2 N

173) Two straight and long conductors AOB and COD are perpendicular to each other and carry currents of I1 and I2. The magnitude of the magnetic field at a point P at a distance a from point O in a direction perpendicular to the plane ABCD is

A) 2102II

a

B) 2102II

a

C) 2/1221202

IIa

D) a

2

0

2121

IIII

174) A straight section PQ of a circuit lies along the x-axis from x = 2a

to x = 2a and

carries a current I. The magnetic field due to the section PQ at point x = + a will be A) proportional to a B) proportional to 2a

C) proportional to a1

D) equal to zero

175) Two very long straight parallel wires carry steady currents I and -I. The distance between the wires is d. At a certain instant of time, a point charge q is at a point equidistance from the two wires, in the plane of the wires. Its instantaneous velocity v is perpendicular to this plane. The magnitude of the force due to the magnetic field acting on the charge at this instant is

A) d

Iqv

20

B) dIqv

0

C) dIqv

02

D) zero

176) A charged particle is released from rest in a region of steady and uniform electric magnetic fields which are parallel to each other. The particle will move in a A) straight line B) circle C) helix D) cycloid

177) A particle of mass 0.6 g and having a charge of 25 nC is moving horizontally with a uniform velocity of 1.2 10-4 m/s in a uniform magnetic field. The value of the magnetic induction is (take g = 10 m/s2) A) zero B) 10 T C) 20 T D) 200 T

178) An electron revolves in a circle of radius 0.4 A with a speed of 106 m/s in Hydrogen atom. The magnetic field produced at the centre of the orbit due to the motion of the electron in tesla is 0 4 10-7 H/m: Charge on the electron 1.6 10-19 C] A) 0.1 B) 1.0 C) 10 D) 100

179) A long wire carries a steady current. It is bent into a circular loop of one turn and the magnetic field at the centre of the loop is B. The wire is then bent into a circular coil of n turns and the same current is passed through it. The magnetic field at the centre of the coil will be A) n B B) n2 B C) 2nB D) 2n2B

180) The magnetic field due to a current carrying circular loop of radius 3 cm at a point on its axis at a distance of 4 cm from the centre is 54 T. The magnetic field (in T) at the centre of the loop will be A) 250 B) 150 C) 125 D) 72

181) The magnetic field due to current element is independent of A) its length B) distance from it C) current through it D) none of the above

182) The unit of a current element is

A) A m B) A m -1 C) A m 2 D) A m 2

183) The magnetic field (B) on the axis of a circular coil and a far away distance r from the centre of the coil are related as A) B r 1 B) B r 2 C) B r -3 D) B r

184) What happens to the magnetic field at the centre of a circular current carrying coil

if we double the radius of the coil keeping the current unchanged? A) halved B) doubled C) quadrupled D) remains unchanged

185) When we double the radius of a coil keeping the current through it unchanged,

what happens to the magnetic field, directed along its axis, at far off points? A) halved B) doubled C) quadrupled D) remains unchanged

186) The strength of the magnetic field around an infinite current carrying conductor is

A) same everywhere B) inversely proportional to the distance C) directly proportional to the distance D) none of these

187) A current carrying power line carries current from west to east. Then the direction

of magnetic field 2 m above it is A) west to east B) south to north C) north to south D) none of these

188) A metallic pipe carries a direct current. Which of the following statements is true

about the existence of a magnetic field? A) The field exists only inside the pipe B) The field exists only outside the pipe C) The field exists inside as well as outside the pipe D) The field exists neither inside nor outside the pipe

189) An infinite straight current carrying conductor is bent into a circle as shown in the figure. If the radius of the circle is r, then the magnetic field at the centre of the coil is

A) zero B) infinite

C) rI

20

D) 12

0

r

I

190) Which of the following is not a unit of magnetic induction?

A) gauss B) tesla C) oersted D) weber/meter2

191) The magnetic field produced by an l metre long straight (very thin) current (I)

carrying conductor at any point on itself is A) zero B) infinite

C) lI4

0

D) lI2

0

192) Which of the following graphs shows the variation of magnetic field (B) with

distance (r) for a long current carrying conductor (fig below)?

193) The magnetic field due to a current carrying torodial solenoid does not depend on the A) radius B) current C) number of turns D) none of these

194) What will be the magnetic field in the empty space enclosed by a toroidal

solenoid of radius r? A) zero B) infinity

C) rI

2

0

D) rI

20

195) What is the magnetic field in the space outside a toroidal solenoid of radius r?

A) zero B) infinity

C) rI

2

0

D) rI

20

196) An infinite long straight wire is bent into a semicircle of radius r. When a current

I is sent through the conductor , the magnetic field at the centre of the semi circle is

A) zero B) infinite

C) rI

20

D) )1(2

0

rI

197) A charge + q is sent through a magnetic field. The force acting on it is maximum when the angle between the direction of motion of the charged particle and the magnetic field is

A) zero B) 45 C) 90 D) 180

198) 1 T is equal to A) 1 N A m B) 1 N A 1 m1 C) 1 N A1 m D) 1 N A m1

199) No force acts on a charge sent through a magnetic field when the angle between

its velocity and the magnetic field is A) 45 B) 90 C) 135 D) 180

200) Out of F

, and B

in the relation F

= q( B

) which of the following pairs

can have any angle between them? A) and B

B) F

and

C) F

and B

D) none of the above

201) The SI unit of magnetic field B is

A) tesla B) gauss C) T m A2 D) A m2

202) 1 tesla equals

A) 106 gauss B) 105 gauss C) 104 gauss D) 10 4 gauss

203) The dimensional formula of magnetic field is

A) MLT2 B) MLT2 T1 C) MLT2 A2 D) ML0T2 A1

204) Which of the following is a unit of magnetic dipole moment?

A) A m2 B) A m2 C) T mA1 D) T m A2

205) Choose the only scalar from among the following: A) electric potential B) drift velocity C) magnetic induction D) magnetic dipole moment

206) Which of the following cannot be deflected while in motion by magnetic fields?

A) protons B) cathode rays C) alpha particles D) neutrons

207) The force between two parallel, infinitely long conductors carrying currents in the same direction will be

A) attractive B) repulsive C) attractive at small distances but repulsive at large distances D) repulsive at small distances but attractive at large distances

208) The force between two parallel, infinitely long conductors carrying currents in opposite directions will be

A) attractive B) repulsive C) attractive at small distances but repulsive at large distances D) repulsive at small distances but attractive at large distances

209) The force on a charged particle in motion due to magnetic field is maximum when

the angle between the direction of motion and the magnetic field is A) 0 B) 90 C) 45 D) 180

210) The dipole moment of a current loop does not depend on the

A) number of turns B) area of the loop C) current in the loop D) magnetic field in which it is kept

211) Which of the following quantities of a particle will not change when a charged particle moves through a magnetic field directed perpendicular to its motion?

A) speed B) momentum C) velocity D) all the above

212) What will be the nature of the path followed by a proton when it enters a magnetic field with its velocity parallel to the magnetic field?

A) circle B) parabola C) straight line D) none of the above

213) A test charge q enters a magnetic field B directed along the Z-axis. The velocity

of the test charge is and it makes angle with B

. What will be the speed of the test charge after 2 s? A) B) /B C) B D) B q

214) Refer to a question 213 above, if = 0 which of the following will change with

time? A) momentum B) kinetic energy C) acceleration D) none of the above

215) Refer to a question 213, if the mass of the charged particle is M, it will revolve

with an angular speed given by A) B q M

B) B

qM

C) MqB

D) qMB

216) Refer to question 213, what is the time rate of work done by the magnetic field on

the test charge when is neither 0 nor 90? A) q B

B) qB

C) q B D) zero

217) Refer to question 213, in which direction does no change in momentum of the

test charge take place? A) along the X-axis B) along the Y-axis C) along the Z-axis D) none of the above

218) Refer to question 213, which of the following associated with the charged

particle does not depend on the mass of the charged particle? A) momentum B) kinetic energy C) centripetal force D) none of the above

219) Two thin long parallel wires separated by a distance b are carrying a current of I

A each. The magnitude of force exerted per unit length by one wire on the other is

A) bI

2

20

B) bI

2

20

C) bI

2

0

D) 20

2 bI

220) The path of a charged particle in a magnetic field when its direction of motion is

not at right angles to field, will be a A) circle B) straight line C) parabola D) helix

221) The path of a charged particle in a magnetic field, when its direction of motion is

at right angles to the field, will be a A) circle B) straight line C) parabola D) helix

222) A proton and an electron enter a magnetic field with equal initial velocities.

Which one of them will experience the greater force? A) proton B) electron C) both will experience the same force D) nothing can be decided

223) If a positively charged particle falls vertically downwards, then the horizontal component of the earths magnetic field will deflect it towards

A) west B) east C) north D) south

224) A proton and an electron enter a magnetic field at right angles to the field with

same kinetic energy. Then A) the trajectory of the electron is less curved B) the trajectory of the protron is less curved C) both the trajectories are equally curved D) nothing can be decided

225) Two long, parallel wires, separated by a distance r, have an equal current I

flowing through them. The magnetic field of one exerts a force F on the other. The distance r is increased to 2r and the current in each wire is reduced from I to I/2. What is the force between them now? A) F B) 4F C) F/4 D) F/8

226) A certain length of wire carries a steady current. It is bent to form a circular coil

of one turn. The same length is now bent more sharply to give a double loop of a smaller radius. The magnetic field at the centre caused by the same current is A) unaltered B) half of its first value C) four times its first value D) a quarter of its first value

227) Under identical conditions, the ratio of the magnetic to the electrostatic force is

A) 1027 B) 1017 C) 10-17 D) 10-27

228) The SI unit for 0 is

A) T B) T m A-1 C) T m A-2 D) T m2 A-1

229) Figure shows a magnetic field perpendicular to the plane of the paper and coming out of it. The curve PQR shows the trajectory of a particle in the plane of the paper. Then the particle is

A) proton B) electron C) neutron D) none of these

230) The radius of the trajectory of a charged particle in a uniform magnetic field is proportional to the

A) charge on the particle B) energy of the particle C) momentum of the particle D) all the above

231) The force F experienced by a particle of charge q moving with velocity in a magnetic field B is given by

A) F = q (v B) B) F = q (B v) C) F = (v B) D) F = q(v . B)

232) In the question above, which pairs of vectors are always at right angles to each

other? A) v, B B) F, v C) F, B D) both (b) and (c)

233) When a charged particle moves perpendicular to a uniform magnetic field, its

A) energy and momentum both change B) energy changes but momentum remains unchanged C) momentum changes but the energy remains unchanged D) both energy and momentum do not change

234) The tangent law is applicable to a dipole placed in two magnetic fields 1B

and 2B

when

A) 1B

= 2B

B) 1B

2B

C) 1B

makes any angle with 2B

D) 1B

is directed opposite to 2B

235) The force on a current carrying conductor in a magnetic field will be maximum

when the angle between the current and magnetic field is A) zero B) 45 C) 90 D) 135

236) No force is exerted by a magnetic field on a stationary

A) electric dipole B) current loop C) magnetic dipole D) current carrying conductor

237) No force is exerted by a magnetic field on a charge if it is

A) at rest B) moving in a circle C) moving with a constant velocity D) moving along a curved path

238) No force acts on a current carrying conductor in a magnetic field, when the angle between the magnetic field and the current is

A) zero B) 45 C) 90 D) 135

239) The torque acting on a magnetic dipole of moment mp

when placed in a magnetic field B

is

A) pm B B) mp

B

C) mp . B

D) BPm

240) A rectangular loop carries a current I. It is placed near a long straight conductor carrying a current I1. Then , the force experienced by the coil is

A) attractive B) repulsive C) no force at all D) repulsive at short distances but attractive at long distances

241) The force between two parallel current carrying conductors is F. If the current in each conductor is doubled, then the force between them becomes

A) 4 F B) 2 F C) F

D) 4F

242) Which of the following graphs shows the variation of force (F) between two fixed current carrying conductors and the distance (d) between them?

243) A current carrying coil is placed in a uniform magnetic field. If the coil turns through an angle , then the torque is directly proportional to A) sin B) cos C) cot D) tan

244) An ammeter has a resistance r and a range I. What resistance should be connected

in parallel with it to increase its range n times.

A) nr

B) 1nr

C) r ( n +1) D) none of these

245) A voltmeter has a resistance r and a range V. What resistance should be connected

in series with it to increase its range to nV ? A) n r B) (n 1) r C) (n + 1) r D) none of the above

246) A galvanometer may be converted into an ammeter or a voltmeter. In which of the following cases will the resistance of the device so obtained be the largest ?

A) ammeter of range 10 A B) ammeter of range 1 A C) voltmeter of range 1V D) voltmeter of range 10 V

247) In question 75 above , the resistance will be least in case of

A) ammeter of range 1 A B) ammeter of range 10 A C) voltmeter of range 1 V D) voltmeter of range 10 V

248) When a galvanometer is shunted with a 20 resistance, its deflection is reduced

to half. Then the resistance of the galvanometer is A) 10 B) 20 C) 40 D) 80

249) A voltmeter of range 3 V and resistance 200 cannot be converted into an ammeter of range A) 1 A B) 20 A C) 10 m A D) 100 m A

250) A vertical wire carries a current upwards. The magnetic field at a point due north

of the wire is directed A) upward B) due south C) due west D) due east

251) Two parallel beams of protons and electrons, carrying qual currents, are fixed at a

separation d. The protons and electrons move in opposite directions. P is a point on a line joining the beams, at a distance x from any one beam. The magnetic field at P is B. If B is plotted against x, which of the following best represents the resulting curve ?

252) Two long thin wires ABC and DEF are arranged as shown. They carry currents I as shown . The magnitude of the magnetic field at o is

A) zero

B) aI

4

0

C) aI

2

0

D) a

I

220

253) AB and CD are long straight conductors, distance d apart, carrying a current I.

The magnetic field at BC due to the currents in AB and CD is

A) zero at all points B) zero only at its midpoint C) different magnitudes at different points D) maximum at its midpoint

254) question 253, the magnetic field at the midpoint of BC has magnitude

A) dI

8

0

B) dI

4

0

C) dI

2

0

D) dI

0

255) A wire carrying a current I is shaped as shown. Section AB is a quarter circle of

radius r. The magnetic field at C is directed

A) along the bisector of the angle ABC, away from AB B) along the bisector of the angle ABC, towards AB C) perpendicular to the plane of the paper, directed into the paper D) at an angle /4 to the plane of the paper

256) In question 255, the magnitude of the magnetic field at C is

A) rI

20

B) rI

40

C) rI

80

D) rI

4

0

257) The wire loop formed by joining two semicircular sections of radii R1 and R2 , and centre C, carries a current I, as shown .The magnetic field at C has magnitude

A) 20 I

21

11RR

B) 40 I

21

11RR

C) 20 I

21

11RR

D) 40 I

21

11RR

258) An electron moving in a circular orbit of radius r makes n rotations per second .

The magnetic field produced at the centre has magnitude A) zero

B) rne

2

0

C) rne

20

D) r

en2

20

259) A flat circular coil of n turns and radius r carries a current i. Its magnetic moment

is A) r2ni B) 2rni

C) 0

r

ni2

D) 0 r2ni

260) A point P lies on the axis of a flat coil carrying a current . The magnetic moment of the coil is .The distance of P from the coil is d, which is large compared to the radius of the coil. The magnetic field at P has magnitude

A) 2

0

3d

B) 4

0

3d

C) 2

0

2d

D) 4

0

2d

261) Current flows through a straight, thin-walled tube of radius r. The magnetic field

at a distance x from the axis of the tube has magnitude B. A) B x, for 0 < x < r B) B 1/x, for 0 < x < r C) B = 0, for 0 x < r D) B = 0, only for x = 0

262) A coaxial cable consists of a thin inner conductor fixed along the axis of a hollow

outer conductor. The two conductors carry equal currents in opposite directions. Let B1 and B2 be the magnetic fields in the regions between the conductors, and outside the conductor, respectively. A) B1 0, B2 0 B) B1 = B2 = 0 C) B1 0, B2 = 0 D) B1 = 0, B2 0

263) In question 262, if both conductors carry equal currents in the same direction,

A) B1 0, B2 0 B) B1 = B2 = 0 C) B1 0, B2 = 0 D) B1 = 0, B2 0

264) In Q. No.263, let B be the magnetic field at a point between the two conductors, at

a distance x from the axis. Let B2 be the magnetic field at a point outside the outer conductor, at a distance 2x from the axis. A) B2 = B1 B) B1 = 2B2 C) B2 = 2B1 D) B2 = 4B1

265) A long straight conductor carrying a current lies along the axis of a ring. The conductor will exert a force on the ring if the ring A) carries a current B) has uniformly distributed charge C) has nonuniformly distributed charge D) none of the above.

266) A closed loop lying in the xy plane carries a current. If a uniform magnetic field B

is present in the region, the force acting on the loop will be zero if B is in A) the x-direction B) the y-direction C) the z-direction D) any of the above direction.

267) A horizontal straight conductor of mass m and length l is placed in a uniform

vertical magnetic field of magnitude B. An amount of charge Q passes through the rod in a very short time such that the conductor begins to move only after all the charge has passed through it. Its initial velocity will be A) BQlm

B) lmBQ

C) m

BQl

D) mQBl .

268) A conductor AB of length l, carrying a current i, is placed perpendicular to a long

straight conductor XY carrying a current I, as shown. The force on AB will act

A) upward B) downward C) to the right D) to the left

269) A square loop ABCD, carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I.

A) There is not net force on the loop. B) The loop will be attracted by the conductor only if the current in the loop

flows clockwise. C) The loop will be attracted by the conductor only if the current in the loop

flows anticlockwise. D) The loop will always be attracted by the conductor.

270) In question 269, the net force on the loop will be

A) 3

2 0 Ii

B)

2

0 Ii

C)

3

2 0 Iil

D)

20 Iil .

271) A flat coil of n turns, area A and carrying a current i is placed in a uniform

magnetic field of magnitude B. The plane of the coil makes an angle with the direction of the field. The torque acting on the coil is A) BinAsin

B) B

nAi sin

C) BinAcos D) Bin2Acos

272) A flat coil carrying a current has a magnetic moment . It is initially in

equilibrium, with its plane perpendicular to a magnetic field of magnitude B. If it is now rotated through an angle , the work done is A) B B) Bcos C) B(1 cos ) D) Bsin

273) The square loop ABCD, carrying a current I, is placed in a uniform magnetic field

B, as shown. The loop can rotate about the axis XX. The plane of the loop makes an angle ( < 900 ) with the direction of B. Through what angle will the loop rotate by itself before the torque on it becomes zero ?

A) B) 900- C) 900 + D) 1800 -

274) A wire is bent to form the double loop shown in the figure. There is a uniform

magnetic field directed into the plane of the loop. If the magnitude of this field is decreasing , current will flow from

A) A to B and C to D B) B to A and D to C C) A to B and D to C D) B to A and C to D

275) A conducting ring R is placed on the axis of a bar magnet M. The plane of R is

perpendicular to this axis. M can move along this axis.

A) M will repel R when it is moving towards R. B) M will attract R when it is moving towards R. C) M will repel R when moving towards as well as away from R. D) M will attract R when moving towards as well as away from R.

276) A conductor PQ, with

PQ =

r , moves with a velocity

in a uniform magnetic

field of induction

B . The emf induced in the rod is

A) (

B ) .

r

B)

. (

Br )

C)

B .(

r )

D)

)( Br

277) A thin semicircular conducting ring of radius R is falling with its plane vertical in

a horizontal magnetic induction

B . At the position MNQ the speed of the ring is . The potential difference developed across the ring is

A) zero

B) 21 B ,2R and M is at a higher potential

C) RB , and Q is at a higher potential D) 2RB ,and Q is at a higher potential

11. MAGNETIC EFFECTS OF ELECTRIC CURRENT

Ques. No. Answer 1 D 2 B 3 B 4 B 5 B 6 D 7 D 8 A 9 C

10 A 11 D 12 D 13 C 14 A 15 A 16 B 17 B 18 B 19 D 20 D 21 A 22 B 23 B 24 D 25 B 26 C 27 B 28 A 29 A 30 C 31 C 32 B 33 B 34 A 35 C 36 C 37 A 38 C 39 A 40 B 41 A 42 D 43 C 44 D 45 C

Ques. No. Answer 46 A 47 B 48 B 49 B 50 A 51 A 52 C 53 D 54 C 55 C 56 C 57 D 58 C 59 B 60 B 61 B 62 B 63 B 64 B 65 C 66 B 67 C 68 D 69 B 70 A 71 B 72 B 73 B 74 C 75 D 76 B 77 A 78 B 79 A 80 C 81 B 82 B 83 C 84 B 85 B 86 A 87 A 88 C 89 A 90 C

Ques. No. Answer 91 A 92 B 93 B 94 C 95 D 96 D 97 C 98 D 99 B 100 B 101 A 102 B 103 C 104 B 105 C 106 A 107 A 108 B 109 D 110 A 111 A 112 A 113 D 114 A 115 B 116 D 117 C 118 A 119 B 120 D 121 C 122 A 123 B 124 A 125 B 126 C 127 B 128 D 129 A 130 B 131 B 132 C 133 B 134 D 135 A

Ques. No. Answer 136 D 137 C 138 B 139 A 140 A 141 B 142 A 143 C 144 C 145 A 146 A 147 D 148 B 149 C 150 C 151 C 152 A 153 D 154 C 155 A 156 C 157 C 158 D 159 C 160 A 161 D 162 D 163 C 164 D 165 A 166 C 167 A 168 D 169 A 170 C 171 B 172 C 173 C 174 D 175 D 176 A 177 C 178 C 179 B 180 A

Ques. No. Answer 181 D 182 A 183 C 184 A 185 C 186 B 187 C 188 B 189 D 190 C 191 A 192 C 193 A 194 A 195 A 196 C 197 C 198 B 199 D 200 A 201 A 202 C 203 D 204 B 205 A 206 D 207 A 208 B 209 B 210 D 211 A 212 C 213 A 214 D 215 C 216 D 217 C 218 C 219 B 220 D 221 A 222 C 223 B 224 B 225 D

Ques. No. Answer 226 C 227 D 228 B 229 A 230 C 231 A 232 C 233 C 234 B 235 C 236 A 237 A 238 A 239 B 240 A 241 A 242 D 243 B 244 B 245 B 246 D 247 B 248 B 249 C 250 C 251 C 252 C 253 C 254 D 255 C 256 C 257 D 258 C 259 A 260 A 261 C 262 C 263 A 264 A 265 D 266 D 267 C 268 A 269 B 270 A

Ques. No. Answer 271 C 272 C 273 C 274 C 275 A 276 A 277 D