Electromechanical device made up of a coil which produces a magnetic field when electric current is passed through it. Such solenoids are used in relaying energy from one device to another, such as from an auto battery to an auto starter. In some applications, the coil surrounds an iron plunger which becomes magnetized and moves in one direction upon application of current. When the flow of current is reversed, the plunger moves in the opposite direction. Such solenoids are used mainly in opening and closing valves.