Q. A solid conducting sphere of radius R and total charge q rotates about its diametric axis with constant angular speed ω . The magnetic moment of the sphere is

(a) $ \displaystyle \frac{1}{3} q R^2 \omega $

(b) $ \displaystyle \frac{2}{3} q R^2 \omega $

(c) $ \displaystyle \frac{1}{5} q R^2 \omega $

(d) $ \displaystyle \frac{2}{5} q R^2 \omega $

Ans: (c)

Sol:

$ \displaystyle \frac{M}{L} = \frac{q}{2m}$