Which of the following is a function of a relay in an electrical circuit?

• A. To convert AC to DC
• B. To act as a switch controlled by electrical signals
• C. To regulate current flow based on temperature
• D. To measure electrical resistance

Answer: (B)

A relay serves a fundamental role in an electrical circuit by acting as a switch controlled by electrical signals. This allows it to enable or interrupt the flow of electricity in a circuit without requiring direct manual operation. When an incoming electrical signal is applied to the relay's control circuit, it activates an electromagnetic coil that causes the relay to either close or open contacts in the circuit. This function is particularly useful in remote switching applications, automation systems, and protecting components by controlling high-voltage or high-current loads with low-voltage signals.

In contrast, converting AC to DC refers to the function of a rectifier rather than a relay. Regulating current flow based on temperature is typically the domain of temperature sensors or controllers, not relays. Measuring electrical resistance involves using devices like ohmmeters or multimeters, which again are specialized tools separate from the functionality of a relay. Thus, the ability of a relay to act as a switch controlled by electrical signals makes it an essential component in many electrical systems.