What is the primary function of a relay in electrical circuits?

A relay primarily serves to control a high-power circuit using a lower-power signal. This is achieved through its design, which consists of an electromagnet and a set of contacts. When a low-power signal energizes the electromagnet, it activates the relay, causing the contacts to either close or open, thereby allowing or interrupting the flow of a high-power circuit without the low-power signal having to handle the high current directly.

This functionality is critical in applications where it’s necessary to control large loads or higher voltages from a safe, low-voltage circuit. For example, in automotive applications, a small switch can activate a relay to turn on headlights, which require more power than the switch can handle alone. The ability to isolate the low-power control circuit from the high-power load enhances safety and efficiency in various electrical systems.

The other options address different concepts. For instance, increasing voltage is typically achieved using transformers, while measuring electrical resistance involves ohmmeters, and converting AC to DC is a function of rectifiers. These roles are distinct from the primary purpose of a relay in electrical circuits.