An electric current is an electric charge flow. In electric circuits, this charge is usually carried by electrons in motion on a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons as in an ionized gas (plasma). The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one Colombian per second. The electric current is measured using a device called an ammeter.
Electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators. Charged charged particles in an electric current are called charge carriers. In metals, one or more electrons of each atom are freely bonded to the atom, and can move freely within the metal. These conduction electrons are the charge carriers in the metal conductors.
The conventional symbol of current is I, which originates from the French phrase intensité de courant (current intensity). The current intensity is often simply referred to as current. The I symbol was used by André-Marie Ampère, after the electric current unit was named, in the formulation of Ampère's strength law (1820). The notation travelled from France to Britain, where it became standard, although at least one magazine did not change from C to I until 1896.