ABSTRACT
This chapter discusses the basic facts about voltage (e.m.f.), current, power and resistance in D.C. circuits. It begins by providing an overview on resistance and goes on to non-linear resistance and the concept of internal resistance of an e.m.f. source. The chapter describes some useful methods of circuit analysis. The magnitude of the current flowing in a circuit depends on the magnitude of the e.m.f. source, and on the device or devices through which the current is flowing. Conductors are made from the materials in which a small potential difference can cause a large current flow. They therefore have very low resistance and high conductance. Copper is the most commonly encountered conducting material; other examples of good electrical conductors are aluminium, silver, gold and platinum. An ideal current source is a source whose current remains unchanged, whatever the load may be.
