Electrical current resulting from the motion of free charges under the influence of an electric field. The density of conduction current J at a point in an isotropic medium is , where is the conductivity and E is the electric field. Conduction currents usually are more important than displacement currents in electromagnetic prospecting, depending on the frequency range. Since in general J and E are vectors, the conductivity is a symmetric tensor given in Cartesian coordinates by
If one of the coordinates is in the direction of maximum conductivity and one in the direction of minimum conductivity, nondiagonal elements vanish. In isotropic materials .