Consider a non conducting plate of radius `a` and mass `m` which has a charge `q` distributed uniformly over it, The plate is rotated about its own axis with a angular speed `omega`. Show that the magnetic moment `M` and the angular momentum `L` of the plate are related as `(M)/(L)=(q)/(2m)`.

Explanation

Considering the strip of with dx at a dist x from center
`da = 4 pi xx dx`
`I = (dq)/(dt) = (qw)/(2 pi)`
`mu = (qw)/(2 pi ) 4 pi int xdx`
`= q . Wr^(2) = (q)/(m) l`