Two identical conducing ring A and B of radius R are in pure rolling over a horizontal conducing plane with same speed (of center of mass) v but in opposite direction. A constant magnetic field B is present pointing inside the plane of paper. Then the potential difference between the highest points of the two rings, is:

Options

A. Zero
B. 2BvR
C. 4BvR
D. None of these

Answer

C

Explanation

Considering a projected length 2R on the ring in verticle plan. This length will move at a speed v perpendicular to the field.
This results in an induced emf:
In Ring "A" : `e_(A)`= BV(2R)
In Ring "B" : `e_(B)` = B(V)(2R) ltBrgt `therefore` potential difference between upper polints
=BV(2R) + BV(2R)=4BVR