A thin semicircular ring of radius 'a' is falling with its plane vertical to a horizontal magnetic field induction $\overrightarrow {B}$ .At the given position PQR the speed of ring is 'v' , the potential difference developed across the ring.

Question

$(a)\;\text{zero} \\(b)\;\text{P will be with higher potential 2aBv} \\ (c)\;\text{R will be with higher potential 2aBv}\\ (d)\;\text{R will be with higher potential $\pi Bv $} $