Class 12 Electromagnetic Induction CBSE Questions & Answers

Class 12 · Electromagnetic Induction

This is Physics Class 12 Electromagnetic Induction CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

ring. 6.6 A circular coil of radius 8.0 cm and 20 turns is rotated about its vertical diameter with an angular speed of 50 rad \({{\rm{s}}^{ - {\rm{1}}}}\) in a uniform horizontal magnetic field of magnitude \({\rm{3}}.0{\rm{ }} \times {\rm{ 1}}0 - {\rm{2}}\) T. If the coil resistance is \({\rm{1}}0{\rm{ }}\Omega \), maximum emf induced in the coil,maximum value of current in the coil and average power loss due to Joule heating are

A
0.603 V, 0.0303 A,0.018 W
B
0.303 V, 0.0603 A,0.018 W
C
0.603 V, 0.0603 A,0.018 W .
Correct
D
0.603 V, 0.0603 A,0.038 W

A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5.0 m \({{\rm{s}}^{ - {\rm{1}}}}\), at right angles to the horizontal component of the earth’s magnetic field, \(0.{\rm{3}}0{\rm{ }} \times {\rm{ 1}}0 - {\rm{4}}\) Wb m-2. Instantaneous value of the emf induced in the wire,direction of the emf and end of the wire which is at the higher electrical potential are

A
\({\rm{1}}.{\rm{5 }} \times {\rm{ 1}}0 - {\rm{3 V}}\), West to East, Eastern end. .
Correct
B
\({\rm{1}}.{\rm{5 }} \times {\rm{ 1}}0 - {\rm{3 V}}\), East to West, Eastern end.
C
\({\rm{1}}.{\rm{6 }} \times {\rm{ 1}}0 - {\rm{3 V}}\), West to East, Eastern end.
D
\({\rm{1}}.{\rm{5 }} \times {\rm{ 1}}0 - {\rm{3 V}}\), West to East, Western end.

Current in a circuit falls from 5.0 A to 0.0 A in 0.1 s. If an average emf of 200 V induced, estimate of the self-inductance of the circuit is

A
5H
B
3H
C
2H
D
4H .
Correct

A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20 A in 0.5 s, change of flux linkage with the other coil is

A
30 Wb .
Correct
B
45 Wb
C
35 Wb
D
40 Wb

A jet plane is travelling towards west at a speed of 1800 km/h. If the Earth’s magnetic field at the location has a magnitude of \({\rm{5 }} \times {\rm{ 1}}0 - {\rm{4 T}}\) and the dip angle is \({\rm{3}}0^\circ \), voltage difference developed between the ends of the wing having a span of 25 m is approximately

A
3.7 V
B
3.5 V
C
3.1 V .
Correct
D
3.3 V

A square loop of side 12 cm with its sides parallel to X and Y axes is moved with a velocity of 8 cm \({{\rm{s}}^{ - {\rm{1}}}}\) in the positive x-direction in an environment containing a magnetic field in the positive z-direction. The field is neither uniform in space nor constant in time. It has a gradient of \({\rm{1}}0{^{ - {\rm{3}}}}{\rm{T c}}{{\rm{m}}^{ - {\rm{1}}}}\) along the negative x-direction (that is it increases by \({\rm{1}}0{^{ - {\rm{3}}}}{\rm{T c}}{{\rm{m}}^{ - {\rm{1}}}}\) as one moves in the negative x-direction), and it is decreasing in time at the rate of \({\rm{1}}0{^{ - {\rm{3}}}}{\rm{T }}{{\rm{s}}^{ - {\rm{1}}}}\).If loop resistance is \({\rm{4}}.{\rm{5}}0{\rm{ m}}\Omega \) . direction and magnitude of the induced current in the loop is

A
\({\rm{13}}.{\rm{96 }} \times {\rm{ 1}}0-{\rm{5 V}},{\rm{ 2}}.{\rm{88 }} \times {\rm{ 1}}0-{\rm{2 A}}\)
B
\({\rm{12}}.{\rm{96 }} \times {\rm{ 1}}0-{\rm{5 V}},{\rm{ 2}}.{\rm{88 }} \times {\rm{ 1}}0-{\rm{2 A}}\)
Correct
C
\({\rm{14}}.{\rm{96 }} \times {\rm{ 1}}0-{\rm{5 V}},{\rm{ 2}}.{\rm{88 }} \times {\rm{ 1}}0-{\rm{2 A}}\)
D
\({\rm{15}}.{\rm{96 }} \times {\rm{ 1}}0-{\rm{5 V}},{\rm{ 2}}.{\rm{88 }} \times {\rm{ 1}}0-{\rm{2 A}}\)

It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area 2 \({\rm{c}}{{\rm{m}}^{\rm{2}}}\) with 25 closely wound turns, is positioned normal to the field direction, and then quickly snatched out of the field region. Equivalently, one can give it a quick \({\rm{9}}0^\circ \) turn to bring its plane parallel to the field direction). The total charge flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5 mC. The combined resistance of the coil and the galvanometer is \(0.{\rm{5}}0{\rm{ }}\Omega \) . Field strength of magnet is

A
0.75 T .
Correct
B
0.90 T
C
0.85 T
D
0.65 T

Figure shows a metal rod PQ resting on the smooth rails AB and positioned between the poles of a permanent magnet. The rails,the rod, and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = \({\rm{9}}.0{\rm{ m}}\Omega \). Assume the field to be uniform. Suppose K is open and the rod is moved with a speed of 12 cm {tex}{{\rm{s}}^{-{\rm{1}}}}{tex} in the direction shown. Polarity and magnitude of the induced emf are

A
8.0 mV,P positive end
B
8.0 mV,P negative end
C
9.0 mV,P negative end
D
9.0 mV,P positive end .
Correct

An air-cored solenoid with length 30 cm, area of cross-section 25 \({\rm{c}}{{\rm{m}}^{\rm{2}}}\) and number of turns 500, carries a current of 2.5 A. The current is suddenly switched off in a brief time of \({\rm{1}}{0^{-{\rm{3}}}}\) s. Average back emf induced across the ends of the open switch in the circuit is

A
7.5 V
B
5.5 V
C
6.5 V .
Correct
D
4.5 V

Expression for the mutual inductance between a long straight wire and a square loop of side a as shown in figure is

A
\(\frac{\mu_0}{2\pi} ln(1 + \frac{1}{x^2})\)
B
\(\frac{\mu_0 a}{2\pi} ln(1 + \frac{1}{x})\) .
Correct
C
\(\frac{ a}{2\pi} ln(1 + \frac{1}{x})\)
D
\(\frac{\mu_0 a}{2\pi} ln(1 + \frac{1}{x})\)

A straight wire carries a current of 50 A and the loop as in figure is moved to the right with a constant velocity, \({\rm{v }} = {\rm{ 1}}0{\rm{ m}}/{\rm{s}}\) . Take a \( = {\rm{ }}0.{\rm{1 m}}\) and assume that the loop has a large resistance. Induced emf in the loop at the instant when x = 0.2 m is

A
\({\rm{2}}.{\rm{3 }} \times {\rm{ 1}}0-{\rm{5 V}}\)
B
\({\rm{1}}.{\rm{7 }} \times {\rm{ 1}}0-{\rm{5 V}}\)
Correct
C
\({\rm{2}}.0{\rm{ }} \times {\rm{ 1}}0-{\rm{5 V}}\)
D
\({\rm{2}}.{\rm{6 }} \times {\rm{ 1}}{0^{-{\rm{5}}}}{\rm{V}}\)

A line charge λ per unit length is lodged uniformly onto the rim of a wheel of mass M and radius R. The wheel has light non-conducting spokes and is free to rotate without friction about its axis (see figure). A uniform magnetic field extends over a circular region within the rim. It is given by, \({\rm{k }}\left( {{\rm{r }} \le {\rm{ a}};{\rm{ a }} < {\rm{ R}}} \right){\rm{ }} = {\rm{ }}0\) (otherwise) Angular velocity of the wheel after the field is suddenly switched off?

A
\(\frac{B\pi a^2\lambda}{MR}k\) .
Correct
B
\(\frac{B a^2\lambda}{MR}k\)
C
\(\frac{B\pi a^3\lambda}{MR}k\)
D
\(\frac{\pi a^2\lambda}{MR}k\)

Two ends of a horizontal conducting rod of length l are joined to a voltmeter. The whoe arrangement moves with a horizontal velocity v, the directio of motion being perpendicular to the rod. Vertical component of the earth's magnetic field is B. The voltmeter reads

A
Blv only if the rod moves eastward
B
Blv if the rod moves in any direction
C
zero .
Correct
D
Blv only if the rod moves westward

A horizontal ring of radius r spins about it's axis with an angular velocity \(\omega \) in a uniform magnetic field of magnitude B. Emf induced in the ring is

A
\(\pi {\rm{r2}}\omega {\rm{B}}\)
B
zero .
Correct
C
\(\pi {\rm{r3}}\omega {\rm{B}}\)
D
\({\rm{r2}}\omega {\rm{B}}\)

A coil consists of 200 turns of wire having a total resistance of \({\rm{2}}.0{\rm{ }}\Omega \). Each turn is a square of side 18cm, and a uniform magnetic field directed perpendicular to the plane of the coil is turned on. If the field changes linearly from 0 to 0.50 T in 0.80 s, Magnitude of the induced emf in the coil while the field is changing is

A
2.8 V
B
3.5 V
C
3.8 V
D
4.1 V
Correct