# Torque of charged rotating disc in uniform magnetic field

1. Nov 29, 2015

### charlief

Hi, I'm having an issue with finding a starting point for the following problem. I've looked through my magnetism and electrodynamic notes but was unable to find a starting point. Could someone please help direct me on the correct path? Thank you.
1. The problem statement, all variables and given/known data
A thin circular disc of radius $R$ rotates with angular speed $\omega$ about an axis through
the centre of the disc and perpendicular to the plane of the disc. A uniform magnetic field
$\mathbf{B}$ acts parallel to the plane of the disc. If the disc is uniformly charged with a surface
density $\sigma$, derive an expression for the magnitude of the torque on the disc, in terms of
$|\mathbf{B}|$, $R$, $\omega$ and $\sigma$.

2. Dec 4, 2015