Electrical current

An electrical current describes the flow of charges through a wire. The units of current are Ampere = Coulombs/second. A charge $Q$ can be stored on a capacitor. If a current $I$ flows onto the capacitor, the charge changes according to,

The current density $\vec{J}(\vec{r})$ is a vector field with units of A/m². The vector points in the direction that the charges are moving. The current density tell us how many Coulombs per second pass the plane perpendicular to the vector $\vec{J}$ per meter squared.

Whenever charge moves, it creates a magnetic field. This is discussed in the next section on magnetism.