Which device is used to control a larger circuit with a smaller control signal?

Which device is used to control a larger circuit with a smaller control signal?

• A. A transformer.
• B. A switch.
• C. A relay.
• D. A fuse.

Answer: (C)

When you want to turn on or off a large circuit using a small control signal, you use a device that acts as an intermediary switch with isolation. A relay fits this role by having a low-power coil on the control side and a set of switch contacts on the load side. Energizing the coil creates a magnetic field that moves the contacts, closing or opening the high-current path. This lets a tiny control signal drive a much larger current or voltage safely, while keeping the control circuit electrically isolated from the load for protection. A transformer changes voltage or current levels but doesn’t switch the load on or off. A switch is a manual device that requires direct action to change state and isn’t typically driven by a separate small control signal. A fuse protects by interrupting current if it gets too high, not for controlling a circuit’s operation.

When you want to turn on or off a large circuit using a small control signal, you use a device that acts as an intermediary switch with isolation. A relay fits this role by having a low-power coil on the control side and a set of switch contacts on the load side. Energizing the coil creates a magnetic field that moves the contacts, closing or opening the high-current path. This lets a tiny control signal drive a much larger current or voltage safely, while keeping the control circuit electrically isolated from the load for protection.

A transformer changes voltage or current levels but doesn’t switch the load on or off. A switch is a manual device that requires direct action to change state and isn’t typically driven by a separate small control signal. A fuse protects by interrupting current if it gets too high, not for controlling a circuit’s operation.