Question

A thin ring of radius `R` metre has charge `q` coulomb uniformly spread on it. The ring rotates about its axis with a constant frequency of `f` revolution/s. The value of magnetic induction in `Wb m^(-2)` at the centre of the ring is
A. `(mu_(0) q f)/(2 R)`
B. `(mu_(0) q)/(2 f R)`
C. `(mu_(0) q)/(2 pi f R)`
D. `(mu_(0) q f)/(2 pi f R)`

Answer 1

Correct Answer - A
We know a revolving ring is equivalnet to a current loop, so electric current corresponds to the revolution of electron is `l = qf`
The magnetic field `(B)` at the centre of circular current carrying coil of radius `R` and current `I`.
`B = (mu_(0) i)/(2R)`
`implies B = (mu_(0) q f)/(2R)`