A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20 A in 0.5 s, what is the change of flux linkage with the other coil?
1. 35 Wb
2. 25 Wb
3. 30 Wb
4. 20 Wb
In which of the following devices, the eddy current effect is not used?
1. Electric heater
2. Induction furnace
3. Magnetic braking in train
4. Electromagnet
What is the dimensional formula of magnetic flux?
1.
2.
3.
4.
A cylindrical magnet is kept along the axis of a circular coil. On rotating the magnet about its axis, the coil will have induced in it:
1. | No current |
2. | A current |
3. | Only an e.m.f. |
4. | Both an e.m.f. and a current |
The magnetic flux through a coil varies with time t as shown in the diagram. Which graph best represents the variation of the e.m.f. E induced in the coil with time t?
1. | 2. | ||
3. | 4. |
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 |
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. |
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.
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.
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. |