Question

What is motional emf? State any two factors on which it depends.

Answer 1

Hint: Electromotive force is generated when there is a change of flux present between a coil and the magnets which occurs due to the relative motion of either the coil or the magnet. The electromotive force is generated due to electromagnetic induction given by the Faraday’s law of electromagnetic induction.

Complete answer:
Motional emf stands for motional electromotive force. Emotional emf is the emf induced when a conducting rod moves in a region of magnetic field. The motional emf is produced when a conducting rod is near a coil which is in motion. When there is a moving coil and a magnet, then there occurs a change in flux and as there is relative motion between the coil and the magnets, the flux across the coil changes which produces the emf and hence electromagnetic induction takes place. There has to be non-zero relative motion between the coil and the magnets. This induced Motional emf is calculated from the following:
$$E=vBI$$
Here B is the magnetic field and l is the length of the rod while v is the velocity of rod perpendicular to the length of the rod.
Motional emf depends on the following quantities:
1. The magnitude of length of rod and
2. Velocity of rod
3. Magnetic field.

Note:If the coil and the magnets move simultaneously in the same direction with the same velocity, then the relative motion would be zero and hence there won’t be any current produced and thus there won’t be motional emf as well. Relative motion is needed, even if one of the coils or magnets is stationary, the other one should move.