How does a relay function in an electrical system?

A relay functions in an electrical system primarily by using an electromagnet to control a switch. When an electrical current flows through the coil of the electromagnet, it generates a magnetic field that attracts a movable armature. This movement of the armature opens or closes contacts in the relay, thereby allowing or interrupting the flow of current to another circuit. This operation enables the relay to control high voltage or high current loads using a lower power signal, making it an essential component for controlling circuit operation without needing direct electrical contact.

This method of operation differentiates relays from other components. For instance, the option stating direct connections with a switch does not account for the isolation and control capabilities provided by a relay. Similarly, the conversion of AC to DC is the function of rectifiers, while voltage levels are typically managed by transformers, not relays. Therefore, the unique function of using an electromagnet to activate a switch is what makes option B the correct answer.