Current is a flow of electric charge carriers, usually electrons or electron-deficient atoms. The common symbol for current is the capital letter I. The standard unit is the ampere, symbolized by A. Current is the flow of electric charge carriers such as electrons, which move from negative to positive points.
The SI unit for measuring electric current is the ampere (A). A current ampere is defined as a coulomb of electrical charge that passes through a single point in a second. Electric current is widely used in household and industrial appliances. Electric current, any movement of electric charge carriers, such as subatomically charged particles (for example, electrical current in a cable, where the charge carriers are electrons) is a measure of the amount of charge that passes through any point in the cable per unit of time. In alternating current, the movement of electrical charges is periodically reversed; in direct current it is not.
In many contexts, the direction of current in electrical circuits is taken as the direction of positive charge flow, which is opposite to the actual electron drift. When so defined, the current is referred to as a conventional current. The current in gases and liquids generally consists of a flow of positive ions in one direction together with a flow of negative ions in the opposite direction. To deal with the overall effect of current, its direction is generally considered to be that of the positive charge carrier. A negative charge current moving in the opposite direction equals a positive charge of the same magnitude as moving in the conventional direction and should be included as a contribution to the total current. The current in semiconductors consists of the movement of holes in the conventional direction and electrons in the opposite direction.
There are many other types of currents, such as proton, positron, or charged pion and muon beams in particle accelerators. The electric current generates an accompanying magnetic field, as in electromagnets. When an electric current flows in an external magnetic field, it experiences a magnetic force, as in electric motors. The loss of heat, or energy dissipated, by electrical current in a conductor is proportional to the square of the current. A common unit of electric current is the ampere, which is defined as a flow of one coulomb of charge per second, or 6.2 × 1018 electrons per second.
The centimeter-gram-second current units are the unit of electrostatic charge (esu) per second. One ampere equals 3 × 109 ESU per second.
