Question. If N is the number of turns in a coil, the value of self inductance varies as
(a) N0
(b) N
(c) N2
(d) N–2
Answer
C
Question. A coil having an area A0 is placed in a magnetic field which changes from B0 to 4 B0 in time interval t. The e.m.f. induced in the coil will be
(a) 3A0 B0 / t
(b) 4A0 B0 / t
(c) 3B0 /A0t
(d) 4A0 / B0t
Answer
A
Question. Induced emf in the coil depends upon
(a) conductivity of coil
(b) amount of flux
(c) rate of change of linked flux
(d) resistance of coil
Answer
C
Question. Eddy currents are produced when
(a) a metal is kept in varying magnetic field
(b) a metal is kept in steady magnetic field
(c) a circular coil is placed in a magnetic field
(d) through a circular coil, current is passed
Answer
A
Question. An inductor may store energy in
(a) its electric field
(b) its coils
(c) its magnetic field
(d) both in electric and magnetic fields
Answer
C
Question. Two solenoids of same cross-sectional area have their lengths and number of turns in ratio of 1 : 2. The ratio of self-inductance of two solenoids is
(a) 1 : 1
(b) 1 : 2
(c) 2 : 1
(d) 1 : 4
Answer
B
Question. The back e.m.f. in a d.c. motor is maximum, when
(a) the motor has picked up max speed
(b) the motor has just started moving
(c) the speed of motor is still on the increase
(d) the motor has just been switched off
Answer
A
Question. The mutual inductance between two coils depends on
(a) medium between the coils
(b) separation between the two coils
(c) orientation of the two coils
(d) All of the above
Answer
D
Question. Two identical coaxial circular loops carry current i each circulating in the clockwise direction. If the loops are approaching each other, then
(a) current in each loop increases
(b) current in each loop remains the same
(c) current in each loop decreases
(d) current in one-loop increases and in the other it decreases
Answer
C
Question. According to Faraday’s law of electromagnetic induction
(a) electric field is produced by time varying magnetic flux.
(b) magnetic field is produced by time varying electric flux.
(c) magnetic field is associated with a moving charge.
(d) None of these
Answer
A
Question. A metal rod moves at a constant velocity in a direction perpendicular to its length. A constant uniform magnetic field exists in space in a direction perpendicular to the rod as well its elocity. Select correct statements (s) from the following.
(a) The entire rod is at the same potential
(b) There is an electric field in the rod
(c) The electric potential is highest at the centre
(d) The electric potential is lowest at its centre and increases towards its ends
Answer
B
Question. A wire loop is rotated in a uniform magnetic field about an axis perpendicular to the field. The direction of the current induced in the loop reverses once each
(a) quarter revolution
(b) half revolution
(c) full revolution
(d) two revolutions
Answer
B
Question. If the number of turns per unit length of a coil of solenoid is doubled, the self-inductance of the solenoid will
(a) remain unchanged
(b) be halved
(c) be doubled
(d) become four times
Answer
D
Question. The total charge induced in a conducting loop when it is moved in a magnetic field depend on
(a) the rate of change of magnetic flux
(b) initial magnetic flux only
(c) the total change in magnetic flux
(d) final magnetic flux only
Answer
C
Question. Lenz’s law is consequence of the law of conservation of
(a) energy
(b) momentum
(c) charge
(d) mass
Answer
A
Question. If coefficient of self induction of a coil is 1 H, an e.m.f. of 1V is induced, if
(a) current flowing is 1A
(b) current variation rate is 1 As–1
(c) current of 1A flows for one sec.
(d) None of these
Answer
B
Question. In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency w in a magnetic field B. The maximum value of emf generated in
the coil is
(a) N.A.B.R.ω
(b) N.A.B.
(c) N.A.B.R.
(d) N.A.B.ω
Answer
D
Question. If rotational velocity of a dynamo armature is doubled, theninduced e.m.f. will become
(a) half
(b) two times
(c) four times
(d) unchanged
Answer
B
Question. In a coil of area 10 cm2 and 10 turns with magnetic field directed perpendicular to the plane and is changing at the rate of 108 Gauss/second. The resistance of the coil is 20Ω.
The current in the coil will be
(a) 0.5 A
(b) 5 A
(c) 50 A
(d) 5 × 108 A
Answer
B
Question. A generator has an e.m.f. of 440 Volt and internal resistance of 4000 hm. Its terminals are connected to a load of 4000 ohm. The voltage across the load is
(a) 220 volt
(b) 440 volt
(c) 200 volt
(d) 400 volt
Answer
D
Question. When the current in a coil changes from 2 amp. to 4 amp. in 0.05 sec., an e.m.f. of 8 volt is induced in the coil. The coefficient of self inductance of the coil is
(a) 0.1 henry
(b) 0.2 henry
(c) 0.4 henry
(d) 0.8 henry
Answer
B
Question. A coil has 200 turns and area of 70 cm2. The magnetic field perpendicular to the plane of the coil is 0.3 Wb/m2 and take 0.1 sec to rotate through 180º.The value of the induced e.m.f. will be
(a) 8.4 V
(b) 84 V
(c) 42 V
(d) 4.2 V
Answer
A
Question. Choke coil works on the principle of
(a) transient current
(b) self induction
(c) mutual induction
(d) wattless current
Answer
B
Question. A current i = 2 sin (πt/3) amp is flowing in an inductor of 2 henry. The amount of work done in increasing the current from 1.0 amp to 2.0 amp is
(a) 1 J
(b) 2 J
(c) 3 J
(d) 4 J
Answer
C
Question. If a current increases from zero to one ampere in 0.1 second in a coil of 5 mH, then the magnitude of the induced e.m.f. will be
(a) 0.005 volt
(b) 0.5 volt
(c) 0.05 volt
(d) 5 volt
Answer
C
Question. A coil having 500 square loops each of side 10 cm is placed normal to a magnetic field which increases at the rate of 1 Wb/m2. The induced e.m.f. is
(a) 0.1 V
(b) 5.0 V
(c) 0.5 V
(d) 1.0 V
Answer
B
Question. A circular coil and a bar magnet placed nearby are made to move in the same direction. If the coil covers a distance of 1 m in 0.5. sec and the magnet a distance of 2 m in 1 sec, he induced e.m.f. produced in the coil is
(a) zero
(b) 0.5 V
(c) 1 V
(d) 2 V.
Answer
A
Question. Magnetic flux f in weber in a closed circuit of resistance 10Ω varies with time f (sec) as f = 6t2 – 5t + 1. The magnitude of induced current at t = 0.25s is
(a) 0.2 A
(b) 0.6 A
(c) 1.2 A
(d) 0.8 A
Answer
A
Question. The current in a coil of L = 40 mH is to be increased uniformly from 1A to 11A in 4 milli sec. The induced e.m.f. will be
(a) 100 V
(b) 0.4 V
(c) 440 V
(d) 40 V
Answer
A
Question. The self inductance of the motor of an electric fan is 10 H. In order to impart maximum power at 50 Hz, it should be connected to a capacitance of
(a) 8μF
(b) 4μF
(c) 2μF
(d) 1μF
Answer
D
Question. A 100 millihenry coil carries a current of 1 ampere. Energy stored in its magnetic field is
(a) 0.5 J
(b) 1 J
(c) 0.05 J
(d) 0.1 J
Answer
C
Question. The armature of a dc motor has 20Ω resistance. It draws a current of 1.5 A when run by a 220 V dc supply. The value of the back emf induced in it is
(a) 150 V
(b) 170 V
(c) 180 V
(d) 190 V
Answer
D
Question. The two rails of a railway track, insulated from each other and the ground, are connected to millivoltmeter. What is the reading of the millivoltmeter when a train passes at a speed of 180 km/hr along the track, given that the vertical component of earth’s magnetic field is 0.2 × 10–4 wb/m2 andrails are separated by 1 metre
(a) 10–2 volt
(b) 10mV
(c) 1 volt
(d) 1 mV
Answer
D
Question. A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth’s magnetic field is 0.2 × 10–4T, then the e.m.f. developed between the two ends of the conductor is
(a) 5 mV
(b) 50 μV
(c) 5 μV
(d) 50 mV
Answer
B
Question. Two identical induction coils each of inductance L are jointed in series are placed very close to each other such that the winding direction of one is exactly opposite to that of the other, what is the net inductance?
(a) L2
(b) 2 L
(c) L /2
(d) zero
Answer
D
Question. A coil is wound on a frame of rectangular cross-section. If all the linear dimensions of the frame are increased by a factor 2 and the number of turns per unit length of the coil remains the same, self-inductance of the coil increases by a factor of
(a) 4
(b) 8
(c) 12
(d) 16
Answer
B
Question. A horizontal telegraph wire 0.5 km long running east and west in a part of a circuit whose resistance is 2.5 W. The wire falls to g = 10.0 m/s2 and B = 2 × 10–5 weber/ m2
, then the current induced in the circuit is
(a) 0.7 amp
(b) 0.04 amp
(c) 0.02 amp
(d) 0.01 amp
Answer
C
Question. A long solenoid having 200 turns per cm carries a current of 1.5 amp. At the centre of it is placed a coil of 100 turns of cross-sectional area 3.14 × 10–4 m2 having its axis parallel to the field produced by the solenoid. When the direction of current in the solenoid is reversed within 0.05 sec, the induced e.m.f. in the coil is
(a) 0.48 V
(b) 0.048 V
(c) 0.0048 V
(d) 48 V
Answer
B
Question. Two coils have a mutual inductance 0.005H. The current changes in first coil according to equation I = I0 sin wt where I0 = 10A and w = 100p radian/sec. The max. value ofe.m.f. in second coil is
(a) 2π
(b) 5π
(c) π
(d) 4π
Answer
B
Question. A solenoid has 2000 turns wound over a length of 0.3 m. Its cross-sectional area is 1.2 × 10–3 m2. Around its central section a coil of 300 turns is wound. If an initial current of 2 A flowing in the solenoid is reversed in 0.25 s, the emf induced in the coil will be
(a) 2.4 × 10–4 V
(b) 2.4 × 10–2 V
(c) 4.8 × 10–4 V
(d) 4.8 × 10–2 V
Answer
B
Question. Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area A = 10 cm2 and length = 20 cm. If one of the solenoid has 300 turns and the other 400 turns, their mutual inductance is (μ0 = 4π × 10 –7 Tm A–1)
(a) 2.4p × 10–5 H
(b) 4.8p × 10–4 H
(c) 4.8p × 10–5 H
(d) 2.4p × 10–4 H
Answer
D
Question. A varying current in a coil change from 10A to zero in 0.5 sec. If the average e.m.f induced in the coil is 220V, the selfinductance of the coil is
(a) 5 H
(b) 6 H
(c) 11 H
(d) 12 H
Answer
C
Question. A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when
(a) number of turns in the coil is reduced
(b) a capacitance of reactance XC = XL is included in the same circuit
(c) an iron rod is inserted in the coil
(d) frequency of the AC source is decreased
Answer
C
Question. A magnetic field of 2 × 10–2 T acts at right angles to a coil of area 100 cm2, with 50 turns. The average e.m.f. induced in the coil is 0.1 V, when it is removed from the field in t sec. The value of t is
(a) 10 s
(b) 0.1 s
(c) 0.01 s
(d) 1 s
Answer
B
Question. A conductor of length 0.4 m is moving with a speed of 7 m/s perpendicular to a magnetic field of intensity 0.9 Wb/m2. The induced e.m.f. across the conductor is
(a) 1.26 V
(b) 2.52 V
(c) 5.04 V
(d) 25.2 V
Answer
B
Question. Two identical circular loops of metal wire are lying on a table without touching each other. Loop A carries a current which increases with time. In response the loop B
(a) remains stationary
(b) is attracted by loop A
(c) is repelled by loop A
(d) rotates about is CM with CM fixed
Answer
C
Question. The self inductance L of a solenoid of length l and area of cross-section A, with a fixed number of turns N increases as
(a) l and A increase
(b) l decreases and A increases
(c) l increases and A decreases
(d) both l and A decrease
Answer
B
Question. A wire loop is rotated in a magnetic field. The frequency of change of direction of the induced e.m.f. is
(a) twice per revolution
(b) four times per revolution
(c) six times per revolution
(d) once per revolution
Answer
A
Question. A rectangular coil of 20 turns and area of cross-section 25 sq. cm has a resistance of 100W. If a magnetic field which is perpendicular to the plane of coil changes at a rate of 1000 tesla per second, the current in the coil is
(a) 1 A
(b) 50 A
(c) 0.5 A
(d) 5 A
Answer
C
Question. A cylindrical bar magnet is rotated about its axis. A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then,
(a) a direct current flows in the ammeter A
(b) no current flows through the ammeter A
(c) an alternating sinusoidal current flows through the ammeter A with a time period T = 2π /ω
(d) a time varying non-sinusoidal current flows through the ammeter A.
Answer
B
