An example of a rheostat is:

• A. Ignition switch
• B. Relay
• C. Instrument panel dimmer switch
• D. Brake light switch

Answer: (C)

A rheostat is a device that varies resistance to control the current in a circuit. In cars, the instrument panel dimmer switch uses this principle to adjust dash-light brightness by increasing or decreasing the resistance in the lighting circuit, which changes how much current reaches the instrument lights. That makes the instrument panel dimmer switch the best example of a rheostat. Other items listed aren’t variable resistors: the ignition switch simply connects power in a selective way, a relay is an electromagnetic switch, and the brake light switch functions as a sensor that turns lights on when the pedal is pressed.