Faraday Disk Dynamo

The Faraday disk dynamo is a direct current generator that works on the principle of induction.

It consists of a conducting disk rotating with a constant angular velocity via a conducting shaft, which is placed in a uniform magnetic field perpendicular to the plane of the disk. The rotation of the disk induces a motional emf in it.

Consider a small segment of the disk with a velocity vector tangential to it. The magnetic force on this segment is radially outward. This accumulates free positive charges toward the rim and free negative charges toward the center, resulting in emf.

Integrating the equation of emf within the limits of the segment length and substituting the magnitude of the velocity vector gives the magnitude of the motional emf.

This disk can be connected to the circuit via two stationary brushes, which conduct the current across the closed loop.

According to Lenz's law, the induced current opposes the constant angular velocity of the disk. So, work must be done to keep the disk rotating at constant angular velocity.