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

Options

(a) µ₀q f / 2 R
(b) µ₀q / 2 f R
(c) µ₀q / 2π f R
(d) µ₀q f / 2π R

Correct Answer:

µ₀q f / 2 R

Explanation:

When the ring rotates f Hz, the current flowing in the ring is i = q/T = qf
Magnetic field at the centre of the ring is
B = µ₀I / 2 R = µ₀q f / 2 R