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ELECTRIC CURRENT Whenever there is a net movement of electric charge through a material, an electric current exists. Current = rate at which charge moves I = q/t = charge passing through a given area time interval The unit for current is the ampere (A) One ampere = one coulomb one second The moving charges that make up a current can be positive or negative. However, conventional current is defined as the direction of flow of positive charge. The individual charge carriers actually move fairly slowly through a wire (on the order of centimeters per second.) However, the electric field moves at close to the speed of electromagnetic radiation (3 x 108 m/s). Direct current (DC) flows in only one direction, while alternating current (AC) is continuously alternating direction. Still, at any instant the charges are moving in only one direction. What is the source of these charges? They are located within the wire. When a potential difference is applied to a circuit, the battery supplies the energy. But the charges are already in the wire.