of electricity exists in a region when a net electric charge
is transported from one point to another in that region. Suppose the charge is moving through a wire
. If a charge q
is transported through a given cross section
of the wire in a time t
, then the current through the wire is:
I = q / t
Here, q is in coulombs, t is in seconds, and I is in amperes (1 A = 1 C/s). By custom the direction of the current is taken to be in the direction of flow of positive charge. Thus, a flow of electrons to the right corresponds to a current to the left.