Drift Current Density and Conductivity:
Consider a conductor of length / meters and cross sectional area a square meters, as shown in Fig. Let the number of free electrons available per m3 of the conductor material i.e., electron density be n and E be the applied electric field. Due to the applied electric field, let axial drift velocity of the electrons be v meters / second. The number of electrons crossing any plane P of cross sectional area a in one second = n x (v x a). If e be the charge of each electron, then the total charge carried by electrons in one second = e. n. v. a. The electric current I, defined as the charge flowing per second across any normal plane of the conductor, is given as. Equation is well known as Ohm's law relating conduction current density and applied electric field or applied voltage.