How does a relay function in a circuit?

A relay functions in a circuit by relying on a magnetic field to switch contacts. When an electrical current flows through the coil of the relay, it generates a magnetic field that attracts a movable armature. This armature then closes or opens the contacts connected to the circuit, allowing or interrupting the flow of electricity in a different part of the circuit.

This mechanism is fundamental in controlling larger loads or multiple circuits safely and efficiently, as it allows a low-power signal to control a high-power circuit. The design of relays enables them to isolate different parts of a circuit and provides a way to control high-voltage devices with lower-voltage signals.

In contrast, the other options do not accurately describe the functioning of a relay. For instance, relays do not generate power independently; they control the flow of power based on the magnetic field generated by the current in their coil. Additionally, relays are not always in an 'on' state; they toggle between on and off states based on the current flowing through their coil. Finally, relays can operate at various voltage levels, not exclusively at high voltages, since they can be designed to work with low voltage signals, enabling them to control high voltage circuits safely.