Which device has two input coils and one output coil?

Which device has two input coils and one output coil?

• A. Control transformer
• B. Relay
• C. Inductor
• D. Capacitor

Answer: (A)

Transformers transfer AC power through windings around a magnetic core, and they can be arranged to match different input voltages while providing a separate, lower-voltage output. A control transformer is built with two primary windings (two input coils) that can be wired to suit the available mains voltage—often in parallel for 120 V or in series for 240 V—and a single secondary winding (one output coil) that delivers the low-voltage control power. This setup lets control circuits run safely off the same supply while keeping electrical isolation between the high-voltage side and the control side. The other devices don’t fit this description: a relay has a coil that activates contacts but doesn’t have two primaries and a single secondary; an inductor typically has a single winding used for storing energy or filtering; a capacitor uses two plates to store electrical energy, not windings.

Transformers transfer AC power through windings around a magnetic core, and they can be arranged to match different input voltages while providing a separate, lower-voltage output. A control transformer is built with two primary windings (two input coils) that can be wired to suit the available mains voltage—often in parallel for 120 V or in series for 240 V—and a single secondary winding (one output coil) that delivers the low-voltage control power. This setup lets control circuits run safely off the same supply while keeping electrical isolation between the high-voltage side and the control side.

The other devices don’t fit this description: a relay has a coil that activates contacts but doesn’t have two primaries and a single secondary; an inductor typically has a single winding used for storing energy or filtering; a capacitor uses two plates to store electrical energy, not windings.