Download Electromagnetic Induction

(Q.1) The inductance between A and D is,
( 1 mark )
(Q.2) If the magnetic field is parallel to a surface, then
the magnetic flux through the surface is
( 1 mark )
(Q.3) What is the basic requirement to induce the
electric current in a coil ?
( 1 mark )
(Q.4) Figure shows a straight wire placed between the
pole pieces of a magnet. Induced emf will be
developed across the ends of the wire, when it is
moved towards ________
( 1 mark )
(Q.5) The magnetic flux linked with a coil varies with
time as = 3t2 + 4t + 9 weber. What is the
induced
emf at t = 2 ?
(Q.6) What is motional emf?
( 1 mark )
(Q.7) What is the basic principle of Lenz’s Law.
(Q.8) What is one Henry?
(Q.9) When the number of turns of a coil per unit
length is doubled, its self inductance is ---------
( 1 mark )
( 1 mark )
(Q.10) The induced emf of 2V is generated when the
current in the circuit changes from 4A to 5A in
one millisecond. Self inductance of the circuit is
(A) 8 H
(B) 10 H
(C) 80 H
(D) 2 mH
View Answer
(Q.11) A proton moving with velocity 10 km/s enters a
region of space having a constant magnetic induction
5T. The largest deflecting force experienced by the
particles
(A) 5 × 10–15 N.
(B) 4 × 10–15 N.
(C) 80 x 10–16 N.
(D) 10–13 N.
View Answer
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(Q.12) Two coils are wound on the same iron rod so
that the flux generated by one also passes through
the other. The primary has 100 loops and secondary
has 200 loops. When a current of 2 A flows through
the primary the flux in it is 25 x 10–4Wb. The value of
M between the coils is
(A) 35 mH
(B) 25 mH
(C) 45 mH
(D) 15 mH
View Answer
(Q.13) A magnet is moved towards a coil (i) quickly
and then (ii) slowly, the induced emf is
(A) Larger in case (i)
(B) Larger in case (ii)
(C) Equal in both cases
(D) No emf is induced
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(Q.14) Which of the following instruments do not
make use of eddy currents ?
(A) Electrical brakes.
(B) Induction motor.
(C) Transformer.
(D) Dead beat galvanometer.
View Answer
(Q.15) For a perfect coupling of two coils of
inductance L1 and L2, their mutual inductance M
should be given by
(A) M = L1L2
(B) M = L1/L2
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( 1 mark )
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(C)
(D) M=L1+L2
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(Q.16) What happens to the magnetic flux when
magnet and loop are moving with same velocity and in ( 1 mark )
the same direction.
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(Q.17) What is the basic cause of induced emf?
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( 1 mark )
(Q.18) A cylindrical bar magnet is kept along the axis
of a circular coil. Will there be a current induced in the ( 1 mark )
coil if the magnet is rotated about its axis?
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(Q.19) A closed loop of wire is being moved so that it
remains in a uniform magnetic field. What is the
( 1 mark )
current induced?
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(Q.20) A magnetic field of 20 T acts at right angles to
a coil of area 20 cm2 with 50 turns. The coil is removed
( 1 mark )
from the field in
What is the change in magnetic
flux and induced emf ?
(A) 2 × 104 wb, 2 × 104 V
(B) 2 wb, 2 × 105 V
(C) 2 × 104 wb, 2 × 103 V
(D) 104 wb, 105 V
View Answer
(Q.21) A copper rod moves parallel to the horizontal
direction. The induced emf developed across its ends
due to earth’s magnetic field will be maximum at the
(A) Equator.
(B) Latitude 30°.
(C) Latitude 60°.
(D) Poles.
View Answer
( 1 mark )
(Q.22) A conductor rod AB moves parallel to X-axis in
uniform magnetic field, pointing in the positive Xdirection. The end A of the rod gets
( 1 mark )
(A) Positively charged.
(B) Negatively charged.
(C) Neutral.
(D) First positively charged and then negatively charged.
View Answer
(Q.23) A cylindrical bar magnet is kept along the axis
of a circular coil. On rotating the magnet about its axis ( 1 mark )
the coil will have induced,
(A) Current.
(B) Only emf.
(C) No current.
(D) Current and an emf.
View Answer
(Q.24) In which of the following cases, with a bar
( 1 mark )
magnet and the solenoid, no induced emf is produced.
(A) When magnet is inserted in the coil.
(B) When magnet is withdrawn from the coil.
(C) When coil is moved towards or away from the magnet.
(D) When the relative velocity of the coil w.r.t. the magnet is zero.
View Answer
(Q.25) The induced emf in a coil rotating in a
magnetic field is maximum when the angle between
the plane of the coil and the direction of field is
(A) 900
(B) 450
(C) 300
( 1 mark )
(D) 600
View Answer
(Q.26) Which of the following phenomenon makes
( 1 mark )
use of the electromagnetic induction?
(A) Charging a storage battery
(B) Magnetizing an iron piece with a bar magnet
(C) Generation of hydroelectricity
(D) Magnetizing a soft iron piece by placing inside a current carrying solenoid
View Answer
(Q.27) In a uniform magnetic field of induction B a
wire in the form of a semicircle of radius r rotates
about the diameter of the circle with an angular
frequency . The axis of rotation is perpendicular to
the field. If the total resistance of the circuit is R, the
mean power generated per period of rotation is
( 1 mark )
(A)
(B)
(C)
(D)
View Answer
(Q.28) What is the expression for mutual inductance
of two co-axial soleniods of same length and same
area of cross section?
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(Q.29) A uniform magnetic field is at right angles to
the direction of motion of protons. As a result, the
( 1 mark )
( 1 mark )
protons describe a circular path of radius 2.5 cm. If
speed of the protons is doubled, then the radius of the
circular path will be
(A) 0.5 cm
(B) 2.5 cm
(C) 5 cm
(D) 7.5 cm
View Answer
(Q.30) 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 the ground 5 m
below. If g = 10m/s2 and B = 2 × 10–5weber/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.
View Answer
( 1 mark )
(Q.31) A copper rod of length l is rotated about one
end perpendicular to the uniform magnetic field B with
( 1 mark )
constant angular velocity w. The induced e.m.f.
between two ends is
(A) 1/2 . B w l2
(B) 3/2 . B w l2
(C) 1. B w l2
(D) 2 . B w l2
View Answer
(Q.32) A small bar magnet is being slowly inserted
with constant velocity inside a solenoid as shown in
figure. Which graph best represents the relationship
between emf induced with time is
( 1 mark )
(A)
(B)
(C)
(D)
View Answer
(Q.33) 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
× 10–4m2having its axis parallel to the field produced ( 1 mark )
by the solenoid. When the direction of current in the
solenoid is reversed within 0.05 sec, the induced em.f.
in the coil is,
(A) 0.48 V
(B) 0.048 V
(C) 0.0048 V
(D) 48 V
View Answer
(Q.34) A wire of length 0.1 m moves with a speed of
10 m/s perpendicular to a magnetic field of induction 1 ( 1 mark )
Wb/m2. What is the e.m.f.?
(A) 1 volt
(B) 2 volt
(C) 0.5 volt
(D) None of these
View Answer
(Q.35) A coil of inductance 0.5 H is connected to a 18
volt battery. What is the rate of growth of current?
(A) 23 A/s
(B) 24 A/s
(C) 28 A/s
(D) 36 A/s
View Answer
(Q.36) Two inductors of inductance L each are
connected in series with opposite magnetic fluxes.
What is the resultant inductance?
( 1 mark )
( 1 mark )
(A) 2L
(B) L
(C) Zero
(D) 3L
View Answer
(Q.37) A train is moving in the North-South direction
with a speed of 72 km/hr. Find the amount of emf
generated between two wheels, if the length of axle be ( 2 Marks )
2m. Assume that the vertical component of earth’s
field is 8x10-5wbm-2.
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(Q.38) A coil is removed from a magnetic field (a)
rapidly (b) slowly. In which case , more work will be
done?
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( 2 Marks )
(Q.39) In an AC generator a coil with N turns, all of the
same area A and total resistance R, rotates with
( 2 Marks )
frequency W in a magnetic field B. Find the maximum
value of emf in the coil.
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(Q.40) A metal conductor of length 1m rotates
vertically about one of its ends at angular velocity 5
rad/sec. If the horizontal component of earth’s
magnetic field is 0.2 x 10-4 T, then find the emf
developed between the two ends of the conductor.
View Answer
(Q.41) Define eddy currents. What is its
disadvantage?
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(Q.42) Find the mutual inductance of two coils with
number of turns 500 and 200 each of length 1m and
cross-sectional area 4x10-4m2.
View Answer
(Q.43) Find the self induced emf in a 0.4H coil when
the current in it is changing at the rate of 800A/S.
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(Q.44) A coil of area 10cm2 has 200 turns. Magnetic
field of strength 0.1wb/m2 is perpendicular to the coil.
The field is reduced to zero in 0.1s, then find the
inducd emf in the coil.
View Answer
( 2 Marks )
( 2 Marks )
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(Q.45)
( 3 Marks )
The magnitude of electric current is increasing from A
towards B. If there is any induced current in the loop
as shown in the fig what will be its direction?
View Answer
(Q.46) A magnetic field perpendicular to the plane of a
rectangular frame of wire is concentrated about O. If
the field decreases, will there be any emf induced in
the loop 1?In the loop 2?
( 3 Marks )
View Answer
(Q.47) An electron moves in a circle with uniform
speed in a stationary magnetic field normal to the
plane of the circle. If the field magnitude is made to
( 3 Marks )
increase with time, will the electron speed up or speed
down? Will it continue to revolve in the same circle?
View Answer
(Q.48) A magnet is dropped down a long vertical
copper tube. What will happen to its ultimate motion?
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(Q.49) An inductor coil of inductance 1H stores 32 J
of magnetic field energy and dissipates energy as
heat at the rate of 640w. Find the resistance if this is
joined across a battery.
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(Q.50) When the current changes from +2A to –2A in
0.05 second, an emf of 8 volt is induced in a coil. Find
the co-efficient of self induction of the coil.
View Answer
( 3 Marks )
( 3 Marks )
( 3 Marks )
(Q.51) Explain, whether an induced current will be
developed in a conductor, if it is moved in a direction
parallel to magnetic field.
View Answer
( 3 Marks )
(Q.52) Calculate the rate at which the flux linked with
the generated area changes with time when a rod of
length l is (a)translated (b) rotated in a uniform
magnetic field B as shown in the fig.
( 5 Marks )
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(Q.53) An air-cored solenoid with length 30cm, area of
cross-section 25cm2 and number of turns 500 carries
a current of 2.5A. The current is suddenly switched off
( 5 Marks )
in a brief time of 10-3s. How much is the average back
emf induced across the ends of the open switch in the
circuit?
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(Q.54) A train is moving with speed 72km/hr on a rail
track separated by distance 120cm and vertical
component of earth’s magnetic field is 3x10-4T. Find –
a) the average emf induced across the width of
the train
( 5 Marks )
b) if the resistance between the rails is
100
ohm.Find the retarding force on the
train due to the magnetic field.
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(Q.55) A 0.2m long copper wire with its length parallel
to x-axis moves along Y-axis with a constant velocity
of 4m/sec in a region where a magnetic field of
induction 0.05 Wb/m2 is present, which is pointing
parallel to Z-axis. If the two ends of the wire are
connected to a resistance of 2ohm,calculate.
a) the emf developed between the two ends of
( 5 Marks )
the copper wire.
b) The current in the circuit.
c) The force required to keep the wire moving.
d) The rate at which work is done by the
applied force.
e) The rate at which heat is produced.
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(Q.56) The figure shows a rod moving with velocity v
parallel to a long straight wire carrying a current i.
Calculate the induced emf in the rod.
( 5 Marks )
View Answer