Norton's theorem is a fundamental principle in electrical circuit analysis, often used as an alternative to Thevenin's theorem. Norton's theorem states that any linear electrical network containing voltage and current sources, along with resistances, can be replaced by an equivalent current source in parallel with a single resistor.
More formally, Norton's theorem can be stated as follows:
"In any linear electrical network with multiple voltage and current sources and resistances, the entire network can be replaced by an equivalent current source (I_Norton) connected in parallel with an equivalent resistor (R_Norton). This equivalent current source (I_Norton) has the same magnitude as the total short-circuit current flowing through the original network, while the equivalent resistor (R_Norton) has the same value as the resistance seen between the two terminals of the network when all voltage sources are replaced by short circuits and all current sources are replaced by open circuits."
In essence, Norton's theorem allows us to simplify complex circuits to a more manageable equivalent circuit, which consists of a single current source and a resistor, making calculations and analysis more straightforward.