<P> The theorem also applies to frequency domain AC circuits consisting of reactive and resistive impedances . It means the theorem applies for AC in an exactly same way to DC except that resistances are generalized to impedances . </P> <P> The theorem was independently derived in 1853 by the German scientist Hermann von Helmholtz and in 1883 by Léon Charles Thévenin (1857--1926), an electrical engineer with France's national Postes et Télégraphes telecommunications organization . </P> <P> Thévenin's theorem and its dual, Norton's theorem, are widely used to make circuit analysis simpler and to study a circuit's initial - condition and steady - state response . Thévenin's theorem can be used to convert any circuit's sources and impedances to a Thévenin equivalent; use of the theorem may in some cases be more convenient than use of Kirchhoff's circuit laws . </P> <P> The equivalent circuit is a voltage source with voltage V in series with a resistance R . </P>

What is the practical use of thevenin equivalent circuits