solenoid

Coil of wire, usually cylindrical, in which a magnetic field is created by passing an electric current through it (see electromagnet). This field can be used to temporarily magnetize, and so move, an iron rod placed on its axis. Mechanical valves attached to the rod can be operated by switching the current on or off, so converting electrical energy into mechanical energy. Solenoids are used to relay energy from the battery of a car to the starter motor by means of the ignition switch.

The solenoid has a magnetic field, one end being the north pole and the other end the south pole. A solenoid behaves like any other electromagnet; by changing the direction of the current the position of the north and south poles can be switched. If a larger current is passed through the coil it becomes a stronger magnet.