What does a relay do in an electrical circuit?

A relay functions primarily as an electromechanical switch that can open or close circuits. It utilizes an electromagnetic coil to control the movement of a set of contacts, allowing it to complete or interrupt the flow of electric current in a circuit. This capability is essential for controlling larger power loads with a lower power signal, making relays invaluable in automation, control systems, and safety shutdown procedures.

For instance, when a small voltage is applied to the relay's coil, it generates a magnetic field that pulls the contacts together, closing the circuit and allowing current to pass through. Conversely, when the voltage is removed, the magnetic field dissipates, and the contacts open the circuit, stopping the current flow. Thus, the ability of a relay to switch circuits on or off is its defining feature and primary function within electrical systems.

Other options, such as amplifying current, transforming voltage levels, or measuring resistance, refer to different functions performed by other electrical components like transistors, transformers, or ohmmeters, and are not relevant to the operation of a relay.