CBSE Class 12 Physics Quiz | CBSE Class 12 Physics MCQs & Answers

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81 A paramagnetic sample shows a net magnetisation of 8 Am-1 when placed in an external magnetic field of 0.6 T at a temperature of 4K. When the same sample is placed in an external magnetic field of 0.2 T at a temperature of 16 K, the magnetisation will be [NCERT Exemplar]
A 323 Am-1
B 23 Am-1
C 6 Am-1
D 2.4 Am-1

Answer: 23 Am-1
82 In a permanent magnet at room temperature
A magnetic moment of each molecule is zero.
B the individual molecules have non-zero magnetic moment which are all perfectly aligned.
C domains are partially aligned.
D domains are all perfectly aligned.

Answer: domains are partially aligned.
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83 Two coils are placed closed to each other. The mutual inductance of the pair of coils depends upon
A the rate at which currents are changing in the two coils.
B relative position and orientation of two coils.
C the material of the wires of the coils.
D the currents in the two coils.

Answer: relative position and orientation of two coils.
84 When current in a coil changes from 5 A to 2 A in 0.1 s, average voltage of 50 V is produced. The self-inductance of the coil is
A 1.67 H
B 0.67 H
C 6 H
D 3 H

Answer: 1.67 H
85 A coil having 500 sq. loops of side 10 cm is placed normal to magnetic flux which increases at a rate of 1 T/s. The induced emf is
A 1 V
B 0.1 V
C 5 V
D 0.5 V

Answer: 5 V
86 Lenz’s law of electromagnetic induction is as per law of conservation of
A energy.
B momentum angular.
C charge.
D electromotive force.

Answer: energy.
87 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
88 The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a short galvanometer. The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was
A moving out of the solenoid
B at rest inside the solenoid
C moving towards the solenoid
D moving into the solenoid

Answer: moving out of the solenoid
89 Faraday’s laws are consequence of the conservation of
A energy
B charge
C magnetic field
D both (b) and (c)

Answer: energy
90 Two identical coaxial coils P and Q carrying equal amount of current in the same direction are brought nearer. The current in
A Q increases while in P decreases
B P increases while in Q decreases
C both P and Q increases
D both P and Q decreases

Answer: both P and Q decreases
91 Direction of current induced in a wire moving in a magnetic field is found using
A Fleming’s right hand rule
B Ampere’s rule
C Fleming’s left hand rule
D Right hand clasp rule

Answer: Fleming’s right hand rule
92 Lenz’s law is a consequence of the law of conservation of
A charge
B energy
C induced emf
D induced current

Answer: energy
93 A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, the current will
A increase
B decrease
C remain same
D first increase then decrease

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

Answer: Lenz’s law is a consequence of the law of conservation of momentum..
95 There is a uniform magnetic field directed perpendicular and into the plane of the paper. An irregular shaped conducting loop is slowly changing into a circular loop in the plane of the paper. Then
A current is induced in the loop in the anti-clockwise direction.
B no current is induced in the loop.
C ac is induced in the loop.
D current is induced in the loop in the clockwise direction.

Answer: current is induced in the loop in the anti-clockwise direction.
96 The north pole of a bar magnet is rapidly introduced into a solenoid at one end (say A). Which of the following statements correctly depicts the phenomenon taking place?
A No induced emf is developed.
B The end A of the solenoid behaves like a south pole.
C The end A of the solenoid behaves like north pole.
D The end A of the solenoid acquires positive potential.

Answer: The end A of the solenoid behaves like north pole.
97 A metal plate can be heated by
A passing either a direct or alternating current through the plate.
B placing in a time varying magnetic field.
C cplacing in a space varying magnetic field, but does not vary with time.
D both (a) and (b) are correct.

Answer: both (a) and (b) are correct.
98 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.
99 Which of the following does not use the application of eddy current?
A LED lights
B Induction furnace
C Electric power meters
D Magnetic brakes in trains

Answer: LED lights
100 If number of turns in primary and secondary coils is increased to two times each, the mutual inductance
A remains unchanged 4
B becomes 4 times
C becomes 2 times
D becomes A times

Answer: becomes 4 times

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