A vertical ring of radius `r` and resistance on `R` falls vertically. It is in contact with two vertical rails which are joined at the top. The rails are without friction and resistance. There is a horizontal uniform, magnetic field of magnitude `B` perpendicular to the plane of the ring and the rails. When the speed of the ring is `v` , the current in the section `PQ` is

Options

A. zero
B. `(2Bv)/(R)`
C. `(4Brv)/(R)`
D. `(8Brv)/(R)`

Answer

D

Explanation

`i=(e)/(R//4)=(4e)/(R)=(4.Bv.2r)/(R)=(8Bvr)/(R)` .