Question

A metal sheet is placed in from of a strong magnetic pole. A force is needed to
Neglect any effect of paramagnetism, diamagnetism and gravity.

• A. hold the steel there if the metal is magnetic
• B. hold the sheet there if the metal is nonmagnetic
• C. move the sheet away from the pole with uniform velocity if the metal is mangetic
• D. move the sheet away from the pole with uniform velocity if the metal is nonmagnetic.

Answer 1

Answer: (A), (C), (D)

The correct options are
A hold the steel there if the metal is magnetic
C move the sheet away from the pole with uniform velocity if the metal is nonmagnetic.
D move the sheet away from the pole with uniform velocity if the metal is mangetic

If the the sheet is magnetic. There will be force between the already present magnetic field and the field of the magnetic sheet. Therefore to hold the sheet still, a counter force will be required that cancels the force between the two fields.
If the sheet is either moved away of towards the pole , regardless of whether it is magnetic or non magnetic, the flux will change. By Lenz's Law a current will be induced that induces a magnetic field, which interacts with the already present field to oppose the change in flux that occurs. Therefore a force will be required to move the sheet. If the velocity is uniform, rate of change of flux be uniform.