Materials which allow an electric current to flow easily are known as conductors and those which prevent the flow of an appreciable current are known as insulators. Conductors and insulators are used in electrical circuits to provide paths for and to control the flow of, electric current. Practically all normal materials are either good conductors or good insulators. There are, however, a few materials which fall between these two categories and these are called semiconductors. Semiconductors will be studied in detail when we begin the electronics phase of the course.
The best electrical conductor is silver, but for most purposes its high cost is prohibitive so copper is the standard conductor material. Aluminium is an alternative, but it is not such a good conductor. Brass, which is harder than copper, is commonly used for terminals, switches etc. Tungsten and nickel are used in the construction of lamps and thermionic valves.