Electromagnetic Induction · Question 7

Let us consider two solenoids A and B, made from same magnetic material of relative permeability r and equal area of cross-section. Length of A is twice that of B and the number of turns per unit length in A is half that of B. The ratio of self inductances of the two solenoids, LA : LB is

1. 1 : 2
2. 2 : 1
3. 8 : 1
4. 1 : 8

The magnetic energy stored in an inductor of inductance 4 carrying a current of 2 A is :

1. 4 mJ
2. 8 mJ
3. 8
4. 4

A square loop of side 1 m and resistance 1 is placed in a magnetic field of 0.5 T. If the plane of loop is perpendicular to the direction of magnetic field, the magnetic flux through the loop is

1. 2 weber
2. 0.5 weber
3. 1 weber
4. Zero weber

A big circular coil of 1000 turns and average radius 10 m is rotating about its horizontal diameter at 2 rad s-1. If the vertical component of earth's magnetic field at that place is 2 10-5 T and electrical resistance of the coil is 12.56 , then the maximum induced current in the coil will be

1. 0.25 A
2. 1.5 A
3. 1 A
4. 2 A

The magnetic flux linked to a circular coil of radius R is = 2t3 + 4t2 + 2t + 5 Wb The magnitude of induced emf in the coil at t = 5 s is

1. 192 V
2. 108 V
3. 197 V
4. 150 V

Two conducting circular loops of radii R1 and R2 are placed in the same plane with their centres coinciding. If R1 >> R2, the mutual inductance M between them will be directly proportional to :

1. R22R1
2. R1R2
3. R2R1
4. R12R2

A 800 turn coil of effective area 0.05 m2 is kept perpendicular to a magnetic field 5 10-5 T. When the plane of the coil is rotated by 90 around any of its coplanar axis in 0.1 s, the emf induced in the coil will be :

1. 0.2 V
2. 0.02 V
3. 2 V
4. 2 10-3 V

In which of the following devices, the eddy current effect is not used?

1. magnetic braking in train
2. electromagnet
3. electric heater
4. induction furnace

The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance

1. 0.138 H
2. 138.88 H
3. 1.389 H
4. 13.89 H

A long solenoid of diameter 0.1 m has 2 104 turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0 A from 4 A in 0.05 s. If the resistance of the coil is 10 2 , the total charge flowing through the coil during this time is

1. 16
2. 32
3. 16
4. 32