- Point law: all the current that flows into a node must come out of the node
- Loop law: the sum of the voltage across any closed loop is zero
Any linear circuit can be simplified with a single voltage source and a resistance in series.
The Thevenin voltage is an ideal voltage source equal to the open circuit voltage at the terminals.
The Thevenin resistance r is the resistance measured at terminals AB with all voltage sources replaced by short circuits and all current sources replaced by open circuits.