Electromagnetic Induction · Question 14

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

Figure shows a circuit that contains three identical resistors with resistance R = 9.0 each, two identical inductors with inductance L = 2.0 mH each, and an ideal battery with emf = 18 V. The current i through the battery just after the switch is closed is [figure]

1. 0.2 A
2. 4 A
3. 0 ampere
4. 2 mA

A long solenoid has 1000 turns. When a current of 4 A flows through it, the magnetic flux linked with each turn of the solenoid is 4 10-3 Wb. The self-inductance of the solenoid is

1. 2 H
2. 1 H
3. 4 H
4. 3 H

A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate d Bdt. Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure. Then the e.m.f. generated is [figure]

1. zero in loop 1 and zero in loop 2
2. - d Bdt r2 in loop 1 and - d Bdt r2 in loop 2
3. - d Bdt R2 in loop 1 and zero in loop 2
4. - d Bdt r2 in loop 1 and zero in loop 2

An electron moves on a straight line path XY as shown. The abcd is a coil adjacent to the path of electron. What will be the direction of current, if any, induced in the coil ? [figure]

1. The current will reverse its direction as the electron goes past the coil
2. No current induced
3. abcd
4. adcb

A conducting square frame of side 'a' and a long straight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity 'V'. The emf induced in the frame will be proportional to [figure]

1. 1(2x+a)2
2. 1(2x-a)(2x+a)
3. 1x2
4. 1(2x-a)2

A thin semicircular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure. [figure] The potential difference developed across the ring when its speed is v, is

1. zero
2. Bv r22 and P is at higher potential
3. rBv and R is at higher potential
4. 2rBv and R is at higher potential

A wire loop is rotated in a magnetic field. The frequency of change of direction of the induced e.m.f. is

1. four times per revolution
2. six times per revolution
3. once per revolution
4. twice per revolution