Which device converts electrical energy into mechanical motion using an electromagnet?

• A. Ultrasonic sensor
• B. Capacitor proximity sensor
• C. Electromechanical relay
• D. Reed switch

Answer: (C)

Actuation with an electromagnet is what an electromechanical relay does. When the coil is energized with electrical energy, it creates a magnetic field that pulls an armature and moves contacts or a mechanical load. That direct conversion of electrical energy into physical motion is the defining behavior of a relay, which is exactly why it fits this description.

Ultrasonic sensors rely on emitting and receiving sound waves, not on electromagnetically driven motion. Capacitor proximity sensors detect changes in capacitance caused by nearby objects rather than driving a mechanical action with a coil. Reed switches respond to an external magnetic field to close or open contacts, but they don’t convert electrical energy into motion themselves—they simply change state in response to magnetism.