Which device changes electrical energy into mechanical motion?

The device that changes electrical energy into mechanical motion is a solenoid. A solenoid works by utilizing the principle of electromagnetism; when electrical current passes through a coil of wire, it generates a magnetic field. This magnetic field can then exert a force on a movable metal core (often referred to as the armature) inside the solenoid, causing it to move.

This conversion of electrical energy into mechanical motion is critical in applications such as electric locks, valves, and in various types of automated machinery where precise motion is required in response to electrical signals. Solenoids are widely used in these contexts because they are efficient and can be quickly activated or deactivated.

Other devices listed serve different functions: a relay is primarily used for switching applications rather than direct motion, a power meter measures electrical consumption, and a capacitor stores electrical energy but does not directly convert it into mechanical motion. Understanding the unique function of a solenoid in translating electrical signals into physical movement is essential for grasping the broader concepts of electrical devices and their applications.