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Objective Type Question Answers On Class 12 Physics Chapter 6

Questions
1 Eddy currents are produced when
A A metal is kept in varying magnetic field
B A metal is kept in the steady magnetic field
C A circular coil is placed in a magnetic field
D Through a circular coil, current is passed

Answer:A metal is kept in varying magnetic field
2 The plane in which eddy currents are produced in a conductor is inclined to the plane of the magnetic field at an angle equal to
A 45°
B 0°
C 180°
D 90°

Answer:90°
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3 The self inductance associated with a coil is independent of
A current
B time
C induced voltage
D resistance of coil

Answer:resistance of coil
4 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:8
5 When current i passes through an inductor of self inductance L, energy stored in it is 1/2. L i2. This is stored in the
A current
B voltage
C magnetic field
D electric field

Answer:magnetic field
6 An induced e.m.f. is produced when a magnet is plunged into a coil. The strength of the induced e.m.f. is independent of
A the strength of the magnet
B number of turns of coil
C the resistivity of the wire of the coil
D speed with which the magnet is moved

Answer:the resistivity of the wire of the coil
7 A current carrying infinitely long wire is kept along the diameter of a circular wire loop, without touching it, the correct statement(s) is(are)

I. The emf induced in the loop is zero if the current is constant.

II. The emf induced in the loop is finite if the current is constant.

III. The emf induced in the loop is zero if the current decreases at a steady rate

A I only
B II only
C I and II
D I, II and III

Answer:I only
8 A magnet is moved towards a coil (i) quickly (ii) slowly, then the induced e.m.f. is
A larger in case (i)
B smaller in case (i)
C equal in both the cases
D llarger or smaller depending upon the radius of the coil

Answer:larger in case (i)
9 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:electric field is produced by time varying magnetic flux.
10 Whenever the magnetic flux linked with an electric circuit changes, an emf is induced in the circuit. This is called
A electromagnetic induction
B lenz’s law
C hysteresis loss
D kirchhoff’s laws

Answer:electromagnetic induction
11 A cylindrical bar magnet is rotated about its axis (Figure). A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then

Class 12 Physics Chapter 6 Electromagnetic

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 = 2πω
D a time varying non-sinosoidal current flows through the ammeter.

Answer:a direct current flows in the ammeter A.
12 There are two coils A and B as shown in Figure. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counterclockwise. B is kept stationary when A moves. We can infer that

Class 12 Physics Chapter 6 Electromagnetic

A there is a constant current in the clockwise direction in A.
B there is a varying current in A.
C there is no current in A.
D there is a constant current in the counterclockwise direction in A.

Answer:there is a constant current in the counterclockwise direction in A.
13 An e.m.f is produced in a coil, which is not connected to an external voltage source. This is not due to
A the coil being in a time varying magnetic field.
B the coil moving in a time varying magnetic field.
C the coil moving in a constant magnetic field.
D the coil is stationary in external spatially varying magnetic field, which does not change with time.

Answer:the coil is stationary in external spatially varying magnetic field, which does not change with time.
14 A square of side L metres lies in the x-y plane in a region, where the magnetic field is given by B = B0{li + 3j + 4k) T, where Bo is constant. The magnitude of flux passing through the square is
A 2BoL² Wb.
B 3BoL² Wb.
C 4BoL² Wb.
D √29 BoL² Wb.

Answer:4BoL² Wb.
15 When the rate of change of current is unity, the induced emf is equal to
A thickness of coil
B number of turns in coil
C coefficient of self inductance
D total flux linked with coil

Answer:coefficient of self inductance
16 Identify the wrong statement.
A Eddy currents are produced in a steady magnetic field.
B Eddy currents can be minimized by using laminated core.
C Induction furnace uses eddy current to produce heat.
D Eddy current can be used to produce braking force in moving trains.

Answer:Eddy currents are produced in a steady magnetic field.
17 Which of the following statements is not correct?
A Whenever the amount of magnetic flux linked with a circuit changes, an emf is induced in circuit.
B The induced emf lasts so long as the change in magnetic flux continues.
C The direction of induced emf is given by Lenz’s law.
D Lenz’s law is a consequence of the law of conservation of momentum.

Answer:Lenz’s law is a consequence of the law of conservation of momentum.
18 The magnetic flux linked with a coil of N turns of area of cross section A held with its plane parallel to the field B is
A NAB/2
B NAB
C NAB/4
D Zero

Answer:Zero
19 In a coil of self-induction 5 H, the rate of change of current is 2 As-1. Then emf induced in the coil is
A 10 V
B -10 V
C 5 V
D -5 V

Answer:-10 V
20 A coil of 100 turns carries a current of 5 mA and creates a magnetic flux of 10-5 weber. The inductance is
A 0.2 mH
B 2.0 mH
C 0.02 mH
D 0.002 H

Answer:0.02 mH

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