The point of this week's reading is to get a grip on this whole idea of equivalent circuits. As I recall from my own experience with this course (just slightly after the begining of the universe) this idea of equivalent circuits was one of the more frustrating. This is especially irritating since when you finally start to make sense of it you will wonder why it bothered you so much. Perhaps this will help -- we learn how to determine equivalent resistances (and later capacitances and inductances) so that we had reduce complex sets of resistors to simpler and more easily understood systems. Equivalent circuits are seeking to ask how can I reduce a complex circuit consisting of potentially many power supplies and resistors to a very simple representation that will behave identically. There are two general forms of this -- Norton and Thevenin. Check it out!
What distinguishes a Norton equivalent circuit from a Thevenin equivalent circuit?
Where is the source resistance in each case?
What is the mathematical relationship between the Norton and Thevenin cases and the source resistance?
What are the special circumstances that apply in each case?