Arc, Electric, a sustained electric current passing from one solid electrical conductor, or electrode, to another through air or some other gas. The gas in the space between electrodes becomes an electrical conductor because the current ionizes it (gives the atoms of the gas an electric charge). An electric arc produces light and heat.

Furnaces that produce heat by means of an electric arc are used in foundries to melt iron. Another common use of the electric arc is in welding, where the heat of the arc fuses metals. Arc lamps using carbon electrodes create a bright, white light. They are used in some searchlights and were formerly widely used in the motion-picture industry for lighting scenes and in theater projectors.

An electric arc can be produced by several methods. In one common method, current is applied to two electrodes in contact with each other; when they are slowly pulled apart, an arc is formed.