The current in self inductance L = 40 mH is to be increased uniformly from 1 amp to 11 amp in 4 milliseconds. The e.m.f induced in inductor during process is
100 volt
0.4 volt
4.0 volt
440 volt
If the number of turns per unit length of a coil of solenoid is doubled, the self-inductance of the solenoid will
Remains unchanged
Be halved
Be doubled
Become four times
A varying current in a coil change form 10 A to zero in 0.5 sec. If the average e.m.f induced in the coil is 220V, the self-inductance of the coil is
5 H
6 H
11 H
12 H
The primary winding of transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an A.C. supply of 20 V, 50 Hz. The secondary will have an output of:
2 V, 5 Hz
200 V, 500 Hz
2V, 50 Hz
200 V, 50 Hz
A step-up transformer operates on a 230 V line and supplies a load of 2 ampere. The ratio of the primary and secondary windings is 1: 25. The current in the primary is
25 A
50 A
15 A
12.5 A
Two coils have a mutual inductance 0.005 . The current changes in the first coil according to equation where and 100 radian/sec. The maximum value of e.m.f. in the second coil is
In an inductor of self-inductance mH, current changes with time according to relation . At what time emf is zero ?
4s
3s
2s
1s
A coil of 40 Henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is
20 seconds
5 seconds
1/5 seconds
40 seconds
The core of a transformer is laminated because
The weight of the transformer may the reduced
Rusting of the core may be prevented
Ratio of voltage in primary and secondary may be increased
Energy losses due to eddy currents may be minimized
Two coils of self inductances 2 mH and 8 mH are placed so close together that the effectives flux in one coil is completely linked with the other. The mutual inductance between these coils is
6 mH
4 mH
16 mH
10 mH