question_answer

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) \[\frac{8Brv}{R}\]

Correct Answer: D

Solution :

[d] \[I=\frac{2Brv}{R/2}=\frac{4Brv}{R}\] Current in the top horizontal\[=2I=\frac{8Brv}{R}\]