Question

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

• A. $\frac{\mu_{0} q\,f}{2R}$
• B. $\frac{\mu_{0} q}{2fR}$
• C. $\frac{\mu_{0} q}{2\pi f R}$
• D. $\frac{\mu_{0} q\,f}{2 \pi R}$

Answer 1

Answer: (A)

We know magnetic field
$\beta = \frac{\mu_{0}i}{2R} $
$q =$ it
$ \Rightarrow i = \frac{q}{t} = q\,\,f $
$ \therefore \beta = \frac{\mu_{0} q\,f}{2R}$