Magnetic field due to currentHard
Question
A ring of mass m and radius R is set into pure rolling on horizontal rough surface, in a uniform magnetic field of strength B as shown in the figure. A point charge q of negligible mass is attached to rolling ring. Friction is sufficient so that it does not slip at any point of its motion. (θ is measured in clockwise from positive y-axis) :-
Options
A.Ring will continue to move with constant velocity
B.The value of friction acting on ring is Bqv cos θ
C.The value of friction acting on ring is Bqv sin θ
D.Ring will lose contact with ground if v is greater than 
Solution
F = qv′ Bsin 
= q[2v cos ]B sin = Bqv sin θ
N = mg - 2Bqv ⇒ To loose contact, N = 0
⇒ v =
= q[2v cos ]B sin = Bqv sin θN = mg - 2Bqv ⇒ To loose contact, N = 0
⇒ v =
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