Suppose a uniform magnetic field B perpendicular to the plane of paper point outward is represented in the region ABCD. A rectangular loop PQRS is pulled such that it moves with a velocity V as shown in the diagram.
This way the area of the loop inside the field changes. This induces an e.m.f in the wire. If in a small time , the loop moves a distance , then the decrease in the area of the loop = - lDx.
where
If R is the resistance of the loop,
The direction of the current is given by Fleming's right hand rule. The induced e.m.f. Blv is called motional e.m.f.
The motional e.m.f can be understood by recalling Lorentz force. When the loop moves, the charges inside it moves and so experiences a force = q v b [as the loop is placed in a external magnetic field]. The work done in moving the charge is q v b.l.
Motional e.m.f = B l v
