Final answer:
A brush may be used to supply current to the rotor field windings in an electric generator.
Step-by-step explanation:
In an electric generator, a brush may be used to supply current to the rotor field windings.
The rotor field windings are responsible for producing the magnetic field required for the generation of electricity in the generator.
By supplying current to the rotor field windings using a brush, the generator can maintain a constant magnetic field and continue to produce electricity.