What is a relay primarily used for in an electrical circuit?

A relay is primarily used in electrical circuits to open and close contacts, which allows it to control other devices. When a small control signal is applied to the relay's coil, it creates a magnetic field that either opens or closes the contacts within the relay. This operation facilitates the control of high-power devices or circuits with low-power signals, making relays essential in applications where direct control of high voltage or high current devices is not feasible.

The mechanics of how a relay works allows for isolation between the low-power control circuitry and the high-power system being controlled, ensuring safety and preventing damage. Furthermore, relays are versatile and used in various logic circuits, switching applications, and automation systems to manage electrical loads effectively.

In contrast, while controlling devices manually, activating lights based on proximity, and directly supplying power to components are functions that might operate within an electrical circuit, they do not accurately define the primary function of a relay. The relay's main purpose is indeed the control of contacts to manage the operation of other devices, positioning it as a critical component in electrical control systems.