What is the function of a relay in a circuit?

A relay is an electromechanical switch that allows one circuit to control another circuit. Its primary function is to use a small input current to open or close a separate circuit, effectively enabling a low-power signal to control a high-power load. This is essential in applications where direct control would be impractical or dangerous, as it can isolate the controlling circuit from the one being controlled.

In a relay, when a current flows through the coil, it generates a magnetic field that moves an armature, either making or breaking a connection in the circuit. This mechanism allows a small control signal to manage larger loads without direct electrical connection, enhancing safety and flexibility in electrical designs.

Other options do not describe the function of a relay accurately. For instance, measuring alternating current requires a different type of device, such as a multimeter or ammeter, and relays do not provide backup power, which is typically the role of batteries or uninterruptible power supplies. While some signal-level changes can be involved in certain relay applications, the conversion of high voltage signals to low voltage is not the main function of a relay; this task is more aligned with transformers or other signal conditioning devices.