Question

Two identical conducting rings P & Q of radius R are in pure rolling over a horizontal conducting plane with same speed (of center of mass) ‘v’ but in opposite direction . A constant magnetic field B is present pointing into the plane of paper. Then the potential between the highest points of two rings, is :

• A. zero
  
• B. 2 Bvr
  
• C. 4 Bvr
  
• D. 8 Bvr-

Answer 1

The correct option is C

4 Bvr

Considering a projected length 2 R on the ring in vertical plane.
This length will move at a speed v perpendicular to the field. This results in an induced emf : e = Bv(2R) in the ring
In Ring P : e = A = B (–v)(2R) ; In Ring Q : e = A = B(v) (2R)
Therefore, potential difference between P & Q = B(v) (2R) – B(–v)(2R) = 4 BvR