Which device is commonly used to open or close circuits remotely by energizing a coil?

Which device is commonly used to open or close circuits remotely by energizing a coil?

• A. Fuse
• B. Switch
• C. Relay
• D. Transistor

Answer: (C)

Relays are devices that use a coil to electrically energize and move a magnetic armature, which opens or closes contacts to switch a circuit remotely. This lets a small control current operate a larger load circuit from a distance, while keeping the control and load sides electrically isolated for safety and noise immunity. Relays can be configured as normally open or normally closed and can handle multiple contact sets, making them versatile for aircraft electrical systems. In contrast, fuses simply protect against overcurrent, switches are usually manual, and transistors are solid‑state switches that don’t rely on a moving contact driven by a coil in the same way a relay does.

Relays are devices that use a coil to electrically energize and move a magnetic armature, which opens or closes contacts to switch a circuit remotely. This lets a small control current operate a larger load circuit from a distance, while keeping the control and load sides electrically isolated for safety and noise immunity. Relays can be configured as normally open or normally closed and can handle multiple contact sets, making them versatile for aircraft electrical systems. In contrast, fuses simply protect against overcurrent, switches are usually manual, and transistors are solid‑state switches that don’t rely on a moving contact driven by a coil in the same way a relay does.