The Lorentz rotating disk consists of a copper disk mounted on an axle inside a solenoid. When the solenoid carries a current and the axle and disk rotate an EMF is induced between the centre and rim of the disk.
The magnitude of the EMF is given by Faraday's law:
where
is the flux through the disk. We can calculate the flux through the disk with the aid of the following diagram.
The magnetic field inside the solenoid is assumed to be uniform of magnitude
so
If the disk rotates m times per second then
For a solenoid
so