Norton's Theorem:

Like Thevenin's theorem, Norton's theorem is also often utilized in electronic circuits. As discussed earlier Thevenin's theorem is utilized to simplify a network into a constant voltage source and a series resistance, Norton's theorem may be utilized to simplify a network into a constant current source and a parallel resistance.

In circuit analysis interchange of voltage sources and current sources by use of Thevenin's and Norton's theorem is sometimes extremely useful.

Statement

This theorem states that any two terminal linear network having energy sources and resistors and can be replaced by an equivalent network consisting of a single current source (I_sc or I_N) and a equivalent parallel resistor (R_N).

Where I_N or I_sc is the short circuit current among the two terminals while these terminals are short circuited and R_N is the equivalent resistance as seen from the terminals.