An inverted L shaped conductor PRQ is made by joining two perpendicular conducting rods, each of length 1.5 L, at end R. This structure is y moving in x-y plane containing variable magnetic field, B→=-3xk^ with a velocity vi^+vj^. If potential of P is VP and that of Q is VQ, then value of VP-VQ at the instant when P is at origin as shown in figure, will be