A disc of mass m, radius r and carrying charge q, is rotating with angular speed `omega` about an axis passing through its centre and perpendicular to its plane. Calculate its magnetic moment

Explanation

In the example considered earlier ratio of magnetic moment to angular momentum of electron came equal to `(e)/(2m)`
In general, for a body of mass m carrying charge q uniformly distributed on it `(M)/(L) = (q)/(2m)` Thus for the disc,
`M = (qL)/(2m) = (ql omega)/(2m) = (q (mr^(2))/(2) omega)/(2m) = (q omega r^(2))/(4)`