Thevenin's theorem

Thevenin’s theorem: Any two-terminal bilateral linear DC circuits can be replaced by an equivalent circuit consisting of a voltage source and a series resistor. 

It is applicable to both active and passive elements.

• Thevenin's theorem fails to simplify a complicated series and parallel linear two - terminal network.
• Thevenin's theorem states that a two - terminal electrical circuit (linear) can be replaced by an equivalent circuit consisting of a voltage source Vth in to series with a resistor known as equivalent resistance of entire network.
• For finding Thevenin equivalent impedance Zth, make the voltage source as a short circuit and the current source as an open circuit (i.e. voltage source and current source is replaced by their respective internal resistances).
• Thevenin's theorem is applicable to linear networks only.