In a conductive fluid, such as a plasma, there is a similar effect. Consider a fluid moving with the velocity v in a magnetic field B . The relative motion induces an electric field E which exerts electric force on the charged particles giving rise to an electric current J . The equation of motion for the electron gas, with a number density n e , is written as m e n e d v e d t = − − n e e E + n e m e ν ν ( v i − − v e ) − − e n e v e × × B ,