^emf by changing area

Diagram shows a rectangular loop of length L, breadth b, moved towards a region of uniform magnetic field B at a uniform velocity v.

Due to change in magnetic flux with time the emf induced in the loop is, ε = B L v. This causes current  (clockwise) in loop. Due to current magnetic force acts on length. This tends to retard the loop. In order to pull the wire frame with uniform velocity external force is to be applied on the loop. The rate at which the applied force does work to maintain the velocity of the wire frame is . This work done is actually appearing in the form of electric energy in the loop.