In this section we will look at several circuit theorems, which are effectively strategies for solving different types of circuit problems. There is no new basic electrical theory introduced in this section, each theorem simply involves the application of:

- Ohm's law.
- Khirchhoff's voltage and current laws.
- Adding combinations of series and parallel resistors.

The Theorems we will look at are:

- Thevenin and Norton's theorem, which show how to produce simple equivalent circuits, for more complicated circuits. These equivalent circuits can then be used, to more easily predict some basic characteristics of the original complex circuits.
- The superposition theorem, which shows how to find currents and voltages, in circuits that contain two or more branches and more than one e.m.f .
- The application of Khirchhoff's laws to form simultaneous equations, as an alternative to the superposition theorem.

*If you find it difficult to follow the calculations in this section, you should revise the basic circuit problems
covered earlier*.