Electromagnet

Electromagnet, device consisting of a solenoid (usually a cylindrical coil of insulated wire) in which an iron core is placed. An electric current passed through the coil induces a strong magnetic field along the axis of the helix. When the iron core is placed in this field, microscopic domains that can be considered small permanent magnets in the iron align themselves in the direction of the field, thus increasing greatly the strength of the magnetic field produced by the solenoid. The magnetization of the core reaches saturation once all the domains are completely aligned, and an increase of the current in the solenoid has little further effect. When the current is switched off, the core retains only a weak residual magnetism.

Widely used in technology, electromagnets are the essential components of relays and circuit-breakers. Electromagnets are also used in electromagnetic clutches and brakes. In some trams, electromagnetic brakes grip directly on to the rails. Very large electromagnets having cores several metres in diameter are used in cyclotrons (see Particle Accelerators), and high-power electromagnets are used to lift iron parts or scrap.