A thin semicircular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure.
The potential difference developed across the ring when its speed , is
Motional emf induced in the semicircular ring PQR is equivalent to the motional emf induced in the imaginary conductor PR.
(l= PR = 2r)
Therefore, potential difference developed across the ring is 2rBv with R is at highe rpotential.