A theorem that is used to simplify the analysis of resistive linear networks. The theorem states that if two terminals (A, B) emerge from a network in order to connect to an external circuit, then as far as the external circuit is concerned the network behaves as a voltage generator. The e.m.f. of the voltage generator is equal to VA,B, where VA,B is measured under open-circuit conditions, and it has an internal resistance given by
where IA,B is the short-circuit current.
Norton’s theorem is an equivalent theorem to Thévenin’s theorem and states that the network, under similar circumstances, can also be represented by a current generator shunted by an internal conductance. Proofs of both these theorems depend upon Ohm’s law. Both theorems can also be applied to alternating-current linear networks but the resistance and conductance must be replaced by the complex impedance ZA,B or admittance YA,B, respectively.