A solenoid is an electrical device composed of two electrical conductors wound into a tightly packed helical shape. When a current is applied to the two conductors, a magnetic field is created. This magnetic field creates a force between the two conductors that causes them to move relative to each other, generating a linear motion. This motion can be used to create mechanical energy, such as in an actuator. Solenoids are often used to convert electrical energy into linear motion (actuators) or linear motion into electrical energy (sensors).