Thevenin’s, Norton’s, and Maximum Power Transfer Theorems

This practical scenario shows how Thévenin’s theorem may be used to “model” a complex device as two simple components (voltage source and resistor). Of course, we must make certain assumptions when modeling in this fashion: we assume, for instance, that the arc welder is a linear device, which may or may not be true.

Ask your students what it means for an electrical or electronic component to be considered “linear,” and also what it means to be considered “bilateral.” Can they give examples of components that are nonlinear, and/or unilateral?

I really mean what I say here about looking this up in a textbook. Norton’s Theorem is a very well-covered subject in many books, and so it is perfectly reasonable to expect students will do this research on their own and come back to class with a complete answer.

The follow-up question is very important, because some circuits (especially transistor amplifier circuits) contain both types of sources. Knowing how to consider each one in the process of calculating the Norton equivalent resistance for a circuit is very important. When performing this analysis on transistor amplifiers, the circuit often becomes much simpler than its original form with all the voltage sources shorted and current sources opened!