An inductor is connected to a direct voltage source through a switch. Then:
1. | a very large emf is induced in inductor when the switch is closed. |
2. | a large emf is induced when the switch is opened. |
3. | a large emf is induced whether the switch is closed or opened. |
4. | no emf is induced whether the switch is closed or opened. |
A long solenoid has self-inductance L. If its length is doubled keeping total number of turns constant, then its new self-inductance will be:
1.
2. 2L
3. L
4.
With the decrease of current in the primary coil from 2 A to zero in 0.01 s, the e.m.f. generated in the secondary coil is \(1000~\mathrm{V}\). The mutual inductance of the two coils is:
1. 1.25 H
2. 2.50 H
3. 5.00 H
4. 10.00 H
Two coaxial coils are very close to each other and their mutual inductance is 5 mH. If a current 50 sin 500t is passed in one of the coils, then the peak value of induced e.m.f. in the secondary coil will be:
1. | 5000 V | 2. | 500 V |
3. | 150 V | 4. | 125 V |
Two identical conductors \(P\) and \(Q\) are placed on two frictionless (conducting) rails \(R\) and \(S\) in a uniform magnetic field directed into the plane. If \(P\) is moved in the direction as shown in the figure with a constant speed, then rod \(Q\):
1. | will be attracted toward \(P\) |
2. | will be repelled away from \(P\) |
3. | will remain stationary |
4. | maybe repelled or attracted towards \(P\) |
1. | From \(a\) to \(b\) and from \(c\) to \(d\) |
2. | From \(a\) to \(b\) and from \(f\) to \(e\) |
3. | From \(b\) to \(a\) and from \(d\) to \(c\) |
4. | From \(b\) to \(a\) and from \(e\) to \(f\) |
The magnetic energy stored in a long solenoid of an area of cross-section A in a small region of length L is:
1.
2.
3.
4.
Eddy currents are induced when:
1. A metal block is kept in a changing magnetic field.
2. A metal block is kept in a uniform magnetic field.
3. A coil is kept in a uniform magnetic field.
4. Current is passed in a coil.
When a conducting wire \(XY\) is moved towards the right, a current flows in the anti-clockwise direction. Direction of magnetic field at point \(O\) is:
1. | parallel to the motion of wire. |
2. | along with \(XY\). |
3. | perpendicular outside the paper. |
4. | perpendicular inside the paper. |
A bar magnet is made to fall through a long surface copper tube. The speed \((v)\) of the magnet as a function of time \((t)\) is best represented by:
1. | \(a\) | 2. | \(b\) |
3. | \(c\) | 4. | \(d\) |