What is motional E.M.F? Derive expression for it. Share with your friends Share 11 Neha Gupta answered this Motional emf: When an conducting loop or rod moves in the in an uniform magnetic field, so that flux through the loop changes, due to the change in the flux through the loop, an emf is induced it the loop, which is called motional emf. Lorentz force on the conducting loop is given by:F = qvB sin θlet magnetic field and velocity of the charge are perpendicular to each other.θ = 90F = qvBthis force must be equal to the electrioc force on the charge.qvB = qEE = vBpotential across the rod or conductor whose length is L id given by:V = electric field×length of the conductorV = ELV = BLvWhere V is the motional emf. 26 View Full Answer