ABSTRACT
This chapter develops some of the basic electrical and electronic principles. It begins by explaining a number of useful circuit theorems including those developed by Thevenin and Norton. The notion of internal resistance is fundamental to understanding the behaviour of electrical and electronic circuits and it is worth exploring this idea a little further before the reader takes a look at circuit theorems in some detail. The chapter shows how series, parallel and series/parallel combinations of resistors can be reduced to a single equivalent resistance. Thevenin's theorem reduces a two-terminal network to an equivalent circuit consisting of a constant voltage source and a series resistance, whilst Norton's theorem reduces the same circuit to a constant current source and a parallel resistance. The superposition theorem provides us with a further tool that can be used to solve complex circuits where several sources may be present.
