Question

A thin semicircular conducting ring, of radius R, in falling with its plane vertical in a uniform horizontal magnetic field of strength B. At the position MNQ the speed of the ring is V. The potential difference, developed across the ring, would than be

(1) 1/2 BVπR² with M at higher potential

(2) πRBV , with Q at higher potential

(3) 2RBV, with Q at higher potential

(4) 2R²BV, with M at higher potential

Answer 1

(3) 2RBV, with Q at higher potential

Rate of decrease of area, of the semicircular ring, in the magnetic field, for the position MNQ, will be

As per Lenz’s law, the induced current in the ring must produce magnetic field directed ‘outwards’. Thus Q must be at a higher potential (so as to send the required anticlockwise (induced) current in the ring).