Consider metallic frame MSRN placed in a uniform constant magnetic field. Let the magnetic field be perpendicular to the plane of the coil. Let a metal rod PQ of length l placed on it be moving towards left with a velocity towards left as shown in the figure. Let the distance of PQ from SR be x.
The magnetic flux linked with the area SPQR is:
As the rod PQ is moving towards left with a velocity , x is changing and
This emf is induced in the rod because of the motion of the rod in the magnetic field. Therefore this emf is called motional emf.
