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

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

• A. A passive resistor in series.
• B. A protective device that opens when overcurrent.
• C. A device that stores charge.
• D. A coil-operated switch that controls a high-current circuit with a low-current control signal.

Answer: (D)

Relays use an electromagnet to operate a switch. A low-current control signal energizes the coil, and the magnetic field moves the contacts to complete or break a high-current circuit. This lets a small, safe signal control a powerful load such as a pump, motor, or light, while keeping the control side isolated from the higher-current path. It also enables remote or centralized control and reduces the risk to the control circuitry from the high current. The other options describe different components: a passive resistor in series doesn’t switch loads; a protective device like a fuse or circuit breaker opens on overcurrent; a device that stores charge is a capacitor.

Relays use an electromagnet to operate a switch. A low-current control signal energizes the coil, and the magnetic field moves the contacts to complete or break a high-current circuit. This lets a small, safe signal control a powerful load such as a pump, motor, or light, while keeping the control side isolated from the higher-current path. It also enables remote or centralized control and reduces the risk to the control circuitry from the high current.

The other options describe different components: a passive resistor in series doesn’t switch loads; a protective device like a fuse or circuit breaker opens on overcurrent; a device that stores charge is a capacitor.