A thin semicircular conducting ring (PQR) of radius ‘r’

A thin semicircular conducting ring (PQR) of radius ‘r’ is falling with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across the ring when its speed is v, is :

1. Zero
2. Bvπr² /2 and P is at higher potnetial
3. πrBv and R is at higher potnetial
4. 2rBv and R is at higher potential

Rate of decreasing of area of semicircular ring

=	dA	= (2r)V
	dt

From Faraday’s law of electromagnetic induction

e = -	dθ	= - B	dA	= -B(2rV)
	dt		dt

As induced current in ring produces magnetic field in upward direction hence R is at higher potential.