A non-conducting ring having q uniformly distributed over its circumference is placed on a rough horizontal surface. A vertical time varying magnetic field `B = 4t^(2)` is switched on at time t = 0. Mass of the ring is m and radius is R. The ring starts rotating after 2 s, the coefficient of friction between the ring and the table isA. `(4qmR)/g`B. `(2qmR)/g`C. `(8qR)/(mg)`D. `(qR)/(2mg)`

A non-conducting ring having q uniformly distributed over its circumfe

1.	A non-conducting ring having q uniformly distributed over its circumference is placed on a rough horizontal surface. A vertical time varying magnetic field `B = 4t^(2)` is switched on at time t = 0. Mass of the ring is m and radius is R. The ring starts rotating after 2 s, the coefficient of friction between the ring and the table isA. `(4qmR)/g`B. `(2qmR)/g`C. `(8qR)/(mg)`D. `(qR)/(2mg)`
Answer» Correct Answer - C `ointE.dl=-(d phi)/(dt) rArr Exx2piR=piR^(2)(dB)/(dt) rArr E=R/2xx8t=R8 rArr (qE)R=(mumg)R rArr mu=(8qR)/(mg)`

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