The Electrical Circuit

Materials used in electrical and electronic engineering can be classified in many ways, one of which is their ability to conduct electricity. Broadly speaking, most materials can be described as being conductors, or semiconductors, or insulators. Conductors are materials which readily allow current flow to occur when an e.m.f. is applied, whereas the current flow in insulators is very small (ideally, it is zero). Semiconductors are materials whose resistance to flow of current lies between that of conductors and that of insulators. A constant or parameter often used to describe the ability of a material to resist the flow of current is its resistivity (see section 1.10 for a full discussion). Using resistivity as a means of defining the above categories of material, conductors have a resistivity in the range from zero to 10−4 ?m, semiconductors have a resistivity in the range 10−4 to 103 ?m, while the resistivity of insulators is above 103 ?m.