A vertical ring of radius r and resistance 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 top horizontal of the rail section is

• A. 0
• B. \[\frac{2Brv}{R}\]
• C. \[\frac{4Brv}{R}\]
• D. \[\frac{8Brv}{R}\]