What is the primary function of an electrical relay?

The primary function of an electrical relay is to control a large current with a smaller current. This is achieved through the use of an electromagnetic switch that opens or closes a circuit depending on the voltage applied to its coil. When a small current flows through the coil, it generates a magnetic field that activates the relay, allowing a larger current to flow through the contacts. This ability makes relays essential in automation and control systems, where they enable low-power control signals to operate high-power devices safely and effectively.

In the context of other options, increasing voltage or converting AC to DC does not accurately represent the function of a relay, as these tasks are typically managed by transformers or rectifiers, respectively. Providing backup power is unrelated to the function of a relay, as this role is filled by devices such as uninterruptible power supplies (UPS) or generators.