CBSE Class 12 Physics Electromagnetic Induction MCQs Set B

Question. Lenz law is based on which of the following conservation>
(a) Charge
(b) Mass
(c) Momentum
(d) Energy

Answer : D

Question. What will be the acceleration of the falling bar magnet which passes through the ring such that the ring is held horizontally and the bar magnet is dropped along the axis of the ring?
(a) It depends on the diameter of the ring and the length of the magnet
(b) It is equal due to gravity
(c) It is less than due to gravity
(d) It is more than due to gravity

Answer : C

Question. How to increase the energy stored in an inductor by four times?
(a) By doubling the current
(b) This is not possible
(c) By doubling the inductance
(d) By making current 2–√ times

Answer : A

Question. Consider an inductor whose linear dimensions are tripled and the total number of turns per unit length is kept constant, what happens to the self-inductance?
(a) 9 times
(b) 3 times
(c) 27 times
(d) 13 times

Answer : B

Question. A coil of copper having 1000 turns is placed in a magnetic field (B = 4 × 10–5) perpendicular to its axis. The cross sectional area of the coil is 0.05 m². If it turns through 180° in 0.01 second, then the e.m.f. induced in the coil will be ;
(a) 4 V
(b) 0.04 V
(c) 0.4 V
(d) 0.2 V

Answer : C

Question. The current in self inductance L = 40 mH is to be increased uniformly from 1 amp to 11 amp in 4 milliseconds. The e.m.f. induced in inductor during process is
(a) 100 volt
(b) 0.4 volt
(c) 4.0 volt
(d) 440 volt

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. In a coil of self inductance of 5 henry, the rate of change of current is 2 ampere per second, the e.m.f. induced in the coil is :
(a) 5 V
(b) – 5V
(c) – 10 V
(d) 10 V

Answer : C

Question. A wheel with ten metallic spokes each 0.50m long is rotated with a speed of 120 rev/min in a plane normal to the earth’ s magnetic field at the place.
If the magnitude of the field is 0.40 G, the induced emf between the axle and the rim of the wheel is equal to
(a) 1.256 × 10 – 3 V
(b) 6.28 × 10 – 4 V
(c) 1.256 × 10 – 4 V
(d) 6.28 × 10 – 5 V

Answer : D

Question. The magnetic flux through a circuit carrying a current of 2.0 A is 0.8 weber. If the current reduces to 1.5 A in 0.1 s, the induced emf be :
(a) 2.0 V
(b) 4.0 V
(c) 8.0 V
(d) none of the options

Answer : A

Question. A charged particle moves through a magnetic field in a direction perpendicular to it. Then the
(a) velocity remains unchanged
(b) speed of the particle remains unchanged
(c) direction of the particle remains unchanged
(d) acceleration remains unchanged

Answer : B

Question. In an inductor of self-inductance L = 2 mH, current changes with time according to relation i = t2e–t. At what time emf is zero?
(a) 4s
(b) 3s
(c) 2s
(d) 1s

Answer : C

Question. A coil of resistance 400 W is placed in a magnetic field. If the magnetic flux f (Wb) linked with the coil varies with time t (sec) as f = 50t2 + 4. The current in the coil at t = 2 sec is
(a) 0.5 A
(b) 0.1 A
(c) 2 A
(d) 1 A

Answer : A

Question. A conducting circular loop is placed in a uniform magnetic field, B = 0.025 T with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of 1 mm s–1. The induced emf when the radius is 2 cm, is
(a) 2Π μV
(b) Π μV
(c) Π/2 μV
(d) 2 μV

Answer : B

Question. A rectangular coil of 20 turns and area of cross-section 25 sq. cm has a resistance of 100 W. 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 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 metal ring is held horizontally and bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is
(a) more than g
(b) equal to g
(c) less than g
(d) either(a) or (c)

Answer : C

Question. A long solenoid of diameter 0.1 m has 2 × 104 turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0 A from 4 A in 0.05 s. If the resistance of the coil is 10 p2 W, the total charge flowing through the coil during this time is
(a) 16 mC
(b) 32 mC
(c) 16p mC
(d) 32p mC

Answer : B

Question. The magnetic flux through a circuit of resistance R changes by an amount Df in a time Dt. Then the total quantity of electric charge Q that passes any point in the circuit during the time Dt is represented by
(a) Q = 1/R . ΔΦ /Δt
(b) Q = ΔΦ/R
(c) Q = ΔΦ /Δt
(d) Q= R.ΔΦ /Δt

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. 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) current is passed through a circular coil

Answer : A

Question. The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance
(a) 0.138 H
(b) 138.88 H
(c) 1.389 H
(d) 13.89 H

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 20W 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. For a coil having L = 2 mH, current flow through it is I = t2e–t then, the time at which emf becomes zero
(a) 2 sec
(b) 1 sec
(c) 4 sec
(d) 3 sec.

Answer : A

Question. Two coils have a mutual inductance 0.005 H. The current changes in the first coil according to equation I = I0 sinwt, where I0 = 10 A and w = 100p rad/sec. The maximum value of e.m.f. in the second coil is
(a) p
(b) 5p
(c) 2p
(d) 4p

Answer : B

Question. If N is the number of turns in a coil, the value of self inductance varies as
(a) N 0
(b) N
(c) N 2
(d) N–2

Answer : C

Question. What is the self-inductance of a coil which produces 5 V when the current changes from 3 ampere to 2 ampere in one millisecond?
(a) 5000 henry
(b) 5 milli-henry
(c) 50 henry
(d) 5 henry

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) four times per revolution
(b) six times per revolution
(c) once per revolution
(d) twice per revolution

Answer : D

Question. According to Lenz’s law there is a conversion of:
(a) momentum
(b) collision
(c) voltage
(d) energy

Answer : D

Question. A 50 turn circular coil has a radius of 3 cm, it is kept in a magnetic field acting normal to the area of the coil. The magnetic field B is increased from 0.10 T to 0.35 T in 2 milli second, the average induced emf will be:
(a) 177 V
(b) 1.77 V
(c) 0.177 V
(d) 17.7 V

Answer : B

Question. A solenoid is 1.5 m long and its inner diameter is 4.0 cm. It has 3 layers of windings of 1000 turns each and carries a current of 2.0 amperes. The magnetic flux for a cross-section of the solenoid is nearly
(a) 4.1´10-5 weber
(b) 5.2´10-5 weber
(c) 6.31´10-3 weber
(d) 2.5´10-7 weber

Answer : C

Question. The flux linked with a coil at any instant ‘t’ is given by Ø = 10t² – 50t + 250. The induced emf at t = 3s is
(a) –190 V
(b) –10 V
(c) 10 V
(d) 190 V

Answer : B

Question. A copper disc of radius 0.1 m rotatniform magnetic field of 0.1 tesla with its plane perpendicular to the field. The e.m.f. induced across the radius of disc is

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. 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. In a region of magnetic induction B = 10–2 tesla, a circular coil of radius 30 cm and resistance p2 ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is
(a) 4p2 mA
(b) 30 mA
(c) 6 mA
(d) 200 mA

Answer : C

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. 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.w
(b) N.A.B.
(c) N.A.B.R.
(d) N.A.B.w

Answer : D

Question. A conducting ring of radius 1 metre is placed in an uniform magnetic field B of 0.01 tesla oscillating with frequency 100 Hz with its plane at right angle to B. What will be the induced electric field ?
(a) pvolt /m
(b) 2volt /m
(c) 10 volt/m
(d) 62 volt/m

Answer : B

Question. A circular disc of radius 0.2 meter is placed in a uniform magnetic field of induction 1/∏ (Wb /m²) in such a way that its axis makes an angle of 60° with –B. The magnetic flux linked with the disc is
(a) 0.08 Wb
(b) 0.01 Wb
(c) 0.02 Wb
(d) 0.06 Wb

Answer : C

Question. A 800 turn coil of effective area 0.05 m2 is kept perpendicular to a magnetic field 5 × 10^–5 T. When the plane of the coil is rotated by 90° around any of its coplanar axis in 0.1 s, the emf induced in the coil will be
(a) 0.02 V
(b) 2 V
(c) 0.2 V
(d) 2 × 10^–3 V

Answer : A

Question. In which of the following devices, the eddy current effect is not used?
(a) electric heater
(b) induction furnace
(c) magnetic braking in train
(d) electromagnet

Answer : A

Question. A long solenoid has 500 turns. When a current of 2 ampere is passed through it, the resulting magnetic flux linked with each turn of the solenoid is 4 × 10^–3 Wb. The self-inductance of the solenoid is
(a) 1.0 henry
(b) 4.0 henry
(c) 2.5 henry
(d) 2.0 henry

Answer : A

Question. A 100 millihenry coil carries a current of 1A. 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. 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. A current of 2.5 A flows through a coil of inductance 5 H. The magnetic flux linked with the coil is
(a) 0.5 Wb
(b) 12.5 Wb
(c) zero
(d) 2 Wb

Answer : B

Question. Faraday’s laws are consequence of conservation of
(a) energy
(b) energy and magnetic field
(c) charge
(d) magnetic field

Answer : A

Question. Two coils of self inductance 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other.
The mutual inductance between these coils is
(a) 16 mH
(b) 10 mH
(c) 6 mH
(d) 4 mH

Answer : D

Question. A cycle wheel of radius 0.5 m is rotated with constant angular velocity of 10 rad/s in a region of magnetic field of 0.1 T which is perpendicular to the plane of the wheel. The EMF generated between its centre and the rim is
(a) 0.25 V
(b) 0.125 V
(c) 0.5 V
(d) zero

Answer : B

Question. A straight line conductor of length 0.4 m is moved 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) 5.04 V
(b) 25.2 V
(c) 1.26 V
(d) 2.52 V

Answer : D