Q. A ring of radius $R$, made of an insulating material carries a charge $Q$ uniformly distributed on it. If the ring rotates about the axis passing through its centre and normal to plane of the ring with constant angular speed $\omega$, then the magnitude of the magnetic moment of the ring is
A) $Q\omega R^{2}$
B) 1/2 $Q\omega R^{2}$
C) $Q\omega^{2}R$
D) 1/2 $Q\omega^{2}R$
Explanation
(b) $M = iA = i \times \pi R^{2}$ also $i = \frac{Q\omega}{2\pi} \Rightarrow M = \frac{1}{2}Q\omega R^{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.