A thin semicircular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction B. At the position MNQ, the speed of the ring is V and the potential difference developed across the ring is

Rate of decrease of area of the semicircular ring  −dAdt=(2R) VAccording to Faraday's law of induction induced emf e=−dφdt=− BdAdt=− B (2RV)The induced current in the ring must generate magnetic field in the upward direction. Thus Q is at higher potential.