Electric Current

The electric current flowing in a conducting medium is defined as

where dQ is the flux of current flowing in time dt. The units of current are Coulomb/sec = Amperes (A).

Conductors have charge carriers (electrons) which drift through the material with an average drift velocity given by

where n is the number of charge carriers per unit volume, A is the cross-sectional area of the conductor, and q is the carrier charge. Since n is typically on the order of Avogadro’s number, the drift velocity for most situations turns out to be fairly low - on the order of a mm/sec.