Question

A metal sheet is placed in front of a strong magnetic pole. A force is needed to
Neglect any paramagnetism, diamagnetism and gravity.
(A) hold the steel there if the metal is magnetic
(B) hold the steel there if the metal is nonmagnetic
(C) move the sheet away from the pole with uniform velocity if the metal is magnetic
(D) move the sheet away from the pole with uniform velocity if the metal is nonmagnetic

Answer 1

Hint
The force will be required in case of magnetic metal as they will be attracted by the magnet. And in case of moving the metal sheet away from the pole, current will be induced in it due to change in flux which will oppose the change.

Complete step by step answer
In the question it is said that a metal sheet is placed in front of a strong magnetic pole. Now due to the properties of the metal if it is magnetic it will be magnetised, and an opposite pole will be induced. Due to this the metal will be pulled by the magnet towards itself. So a force will be required to keep the magnet in place.
If the metal is non-magnetic, there will be no effect on the metal due to the magnet and hence no force will be required to hold the metal in place.
Now whether the metal sheet is magnetic or non magnetic, if it is moved towards or away from the magnetic pole, then from the laws of electromagnetic induction, there will be a change in flux associated with the metal sheet due to the magnetic pole. Now as a result of this magnetic flux, there will be a current induced in the metal sheet. According to Lenz's law, the direction of the current will be such that the magnetic field formed due to that current will oppose the change in flux. So a force will be required.
Therefore, the options (A), (C) and (D) are correct but option (B) is incorrect.

Note
The law of electromagnetic induction or the Faraday’s laws state that whenever there is a change in flux linked with a conductor, there will be a voltage that is induced in the conductor. The magnitude of this voltage will be equal to the rate of change of flux.