A loop `abcd` is moved across the pole pieces of a magnet as shown in fig. with a constant speed `v`. When the edge `ab` of the loop enters the pole pieces at time `t=0` sec. which one of the following graphs represents correctly the induced e.m.f. in the coil if magnetic field lines pass through the loop if it is in between two magnets?

Options

A.
B.
C.
D.

Answer

D

Explanation

When loop enters in field between the pole pieces, flux linked with the coil first increase (constantly)so a constant emf induces, when coil entered completely within the field, no flux change so `e=0`. When coil exit out, flux linked with the coil decreases, hence again emf induces, but in opposite direction.