Electric current

Electric current through a cross-section is the net charge crossing it per unit time: I = q/t for a steady current, or I = dq/dt in general.

The SI unit is the ampere (A), a base unit; 1 A corresponds to 1 C of charge passing per second.

By convention the direction of current is the direction in which positive charge would flow, opposite to the motion of electrons in a metal.

Current has a direction along the wire but is a scalar, because currents at a junction add algebraically, not by vector addition.

Examples span a huge range: lightning carries very large currents for a short time, while currents in electronic devices can be of the order of microamperes or less.