# PHYS345 Class 5

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Source Substitution

Review of Mesh and Nodal Analysis
Mixed Source Example solved by Mesh Analysis and by Nodal Analysis

Thévenin's Theorem

 Any two-terminal linear circuit can be replaced with a voltage source in series with a resistance which will produce the same effects at the terminals. VTh is the open-circuit voltage Voc between the two terminals of the circuit that the Thevenin generator is replacing. RTh is the ratio of Voc to the short-circuit current Isc. In linear circuits, this is equivalent to "killing" the sources and evaluating the resistance between the terminals. Voltage sources are killed by shorting them; current sources are killed by opening them.

Concept Check: Thévenin's Theorem

Norton's Theorem

 Any two-terminal linear circuit can be replaced with a current source in parallel with a resistance which will produce the same effects at the terminals. IN is the short-circuit current Isc of the circuit that the Norton generator is replacing. Again, RN is the ratio of Voc to the short-circuit current Isc. Note that for a given circuit, RN = RTh.

Concept Check: Norton's Theorem