Questions
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]
Answer: 23 Am-1
82
In a permanent magnet at room temperature
Answer: domains are partially aligned.
83
Two coils are placed closed to each other. The mutual inductance of the pair of coils depends upon
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
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
Answer: 5 V
86
Lenz’s law of electromagnetic induction is as per law of conservation of
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
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 The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly.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
Answer: moving out of the solenoid
90
Two identical coaxial coils P and Q carrying equal amount of current in the same direction are brought nearer. The current in
Answer: both P and Q decreases
91
Direction of current induced in a wire moving in a magnetic field is found using
Answer: Fleming’s right hand rule
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
Answer: decrease
94
Which of the following statements is not correct?
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
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?
Answer: The end A of the solenoid behaves like north pole.
98
Identify the wrong statement.
Answer: Eddy currents are produced in a steady magnetic field.
99
Which of the following does not use the application of eddy current?
Answer: LED lights
100
If number of turns in primary and secondary coils is increased to two times each, the mutual inductance
Answer: becomes 4 times
