It used to be thought that when an electric current flowed through a circuit, it was the positive charges which were moving. Now, we realize this is incorrect, and that the negative charges flow through a circuit. They flow from the negative terminal to the positive terminal of the energy force. The electric current from an electric cell flows in one direction. This is called direct current (DC). DC is used in battery-operated devices, such as watches. Alternating current (AC) is used in wall outlets. Alternating current occurs when the electrons periodically reverse direction. In a North American AC unit, the current reverses direction 60 times per second.

An ammeter measures the amount of electric current at a point in a circuit. It is connected in series with the circuit. A multimeter also measures current, among other things.