Solenoid

Solenoid, in electricity, is a coil of insulated wire, usually hollow and cylindrical; its length is generally several times its diameter. A solenoid is the coils of which a current flows acts in most ways like an electro-magnet. An iron core introduced into such a coil is sucked in, and tends to move until the centres of coil and core coincide, and the pull exerted by a solenoid on its core is used for actuating the mechanism of arc lamps and other apparatus, in which a greater range of motion is required than can easily be obtained with an electro~magnet.