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Free download in PDF CBSE Class 12 Physics MCQs & Answers. Here Gkseries provide Physics Solve Questions and Answers for CBSE Class 12 Students.
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
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.
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
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
86
Lenz’s law of electromagnetic induction is as per law of conservation of
[A]
energy.
[B]
momentum angular.
[C]
charge.
[D]
electromotive force.
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
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 The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly.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)
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
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
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
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
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