
2 Resistors
2.1 Introduction
Metals offer very little resistance to the flow of current. Copper is a
good example and is referred to as a conductor. Other materials
such as quartz, polythene and procelain offer very high resistance to
the flow of current and are called insulators.
Intermediate between conductors and insulators are semi-
conductors, the most important being silicon and germanium used
in the manufacture of transistors. Materials made into rods, films
and wire form electronic components which are called resistors.
2.2 Units
The unit of resistance, R, is the ohm, which has the symbol O
(Greek letter omega). The main units are: