Moving Charges and Magnetism - Result Question 38
39. Charge $q$ is uniformly spread on a thin ring of radius $R$. The ring rotates about its axis with a uniform frequency $f Hz$. The magnitude of magnetic induction at the centre of the ring is
[2011M, 2010]
(a) $\frac{\mu_0 q f}{2 R}$
(b) $\frac{\mu_0 q}{2 f R}$
(c) $\frac{\mu_0 q}{2 \pi f R}$
(d) $\frac{\mu_0 q f}{2 \pi R}$
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Answer:
Correct Answer: 39. (a)
Solution:
- (a) When the ring rotates about its axis with a uniform frequency $f Hz$, the current flowing in the ring is
$I=\frac{q}{T}=q f$
Magnetic field at the centre of the ring is
$B=\frac{\mu_0 I}{2 R}=\frac{\mu_0 q f}{2 R}$
