Answer to Question #56033 in Electricity and Magnetism for Misha Jain

Question

A magnet is moved towards a conducting coil along its axis between two fixed positions (i) Quickly and (ii) Slowly, then the work done is and why?
(1) Larger in case (i)
(2) Larger in case (ii)
(3) Equal in both the cases.
(4) None

Answer 1

The emf in the coil produced by the changing magnetic flux is proportional to the time derivative of magnetic flux. This emf produces the current in the coil, which in turn produces the magnetic field of the opposite direction to the magnetic field of the magnet. When you move magnet quickly you must apply greater force (magnetic field of the coil is greater, since the time derivative of magnetic flux is greater) then in the when you move it slowly. Therefore the work is larger in case (i).
Answer: (1)