A solenoid is device that uses the principle of an electromagnet to convert electrical current into mechanical movement. Most typically it is a coil of insulted wire, which, when electric current flows through the wire, has an induced magnetic field inside the coil. This field is used to magnetize a metallic armature or plunger inside the coil--an electromagnet.

Hans Christian Oersted's (1775-1851) discovery in 1820 that an electric current in a wire produced a magnetic field set off a flurry of activity among scientists. In the forefront was André Ampère (1775-1836), whose experiments with electricity and magnetism showed that two parallel wires with electric currents flowing in the same direction attracted each other. When the current flowed in opposite directions, the wires repelled one other. He also experimented with magnetic fields that were created by current flowing in a circular wire and theorized that a helix...