Transconductance Transconductance Transconductance (for transfer conductance), also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device. Conductance is the reciprocal of resistance. Transadmittance (or transfer admittance) is the AC equivalent of transconductance. Transconductance is very often denoted as a conductance, "g", with a subscript, m, for "mutual". It is defined as follows: For small signal alternating current, the definition is simpler: The SI unit, the siemens, with the symbol, S; 1 siemens = 1 ampere per volt replaced the old unit of conductance, having
Current density law (one of Maxwell's equations), which relates current density to magnetic field. In special relativity theory, charge and current are combined into a 4-vector. Charge carriers which are free to move constitute a free current density, which are given by expressions such as those in this section. Electric current is a coarse, average quantity that tells what is happening in an entire wire. At position r at time "t", the "distribution" of charge flowing is described by the current density: where J(r, "t") is the current density vector, v(r, "t") is the particles' average drift velocity (SI unit: m∙s), and