A flexible wire bent in the form of a circle is placed in a uniform magnetic field perpendicular to the plane of the coil. The radius of the coil changes as shown in figure. The graph of induced emf in the coil is represented by

In the r - t graph, it is clear that, from a to b, there is no change in radius and hence no change in area and magnetic flux. Same is the situation from c to d. Now, |e|=dϕdt|e|=Bddtπr2|e|=2πrBdrdt From 0-1, r is constant, ∴drdt=0, hence, |e|=0 From 1-2, r=αt, ∴drdt=α, hence, |e|∝r or |e|∝t From 2-3, again r is constant, ∴drdt=0, hence, |e|=0