A conductor is a material that will permit a ready flow of free electrons through its atomic structure. A good conductor is one that will pass large numbers of free electrons; in other words, one that has a low resistance to the flow of electricity.

There is no such thing as a non-conductive material. All materials conduct electricity; it is more a question of degree and how much electrical force is needed to move electrons through a material.

Silver is the best conducting material, yet copper is the most widely used conductor. Reason for this is that silver is an expensive precious metal whereas copper is more cost effective with conductive properties almost as good as silver.

An insulator is one that has few free electrons to provide high resistance to the flow of electricity. Some common insulators are rubber, plastic, glass, and porcelain.

Glass is a better insulator than rubber but it is brittle whereas rubber is flexible, can be formed into flexible shapes and be used to sheath copper wire.

Semiconductors combine the characteristics of both insulators and conductors, depending on the direction of electron flow.

A conductor will carry a flow of free electrons in any direction. An insulator will resist the flow of electrons in any direction. A semiconductor will let electrons flow in one direction, resisting flow in the opposite direction.

Insulators are as important as conductors in electrical engineering. Together they direct the flow of electricity to where it is needed and prevent it from getting to where it is not needed. Working with electricity can be dangerous; good insulators are very important to safety of life that would otherwise be killed by a lethal flow of electrons.

Conductors and Insulators Combined

Example of effective combination of conductors and insulators is the household light bulb. Its components are:

• Glass Envelope
• Filament
• Wire Conductors
• Supporting Base

Glass Envelope

A glass envelope provides an enclosed low pressure environment for the filament. It is transparent to permit the light to shine forth. It is an insulator to prevent the escape of electricity. The glass envelope provides a means by which the bulb can be gripped during installation and removal.

Filament

The filament is supported at each end by a pair of wires. When electricity flows through the filament it glows bright to produce visible light. Protecting the hot, brittle filament from oxidation and mechanical damage is the glass envelope.

Wire Conductors

A pair of wires support the filament, supplying it with electricity from contacts in the supporting base housing.

Supporting Base

Base of the light bulb provides mechanical support for the bulb assembly and the place through which electricity flows in, via the wires to the filament. Household light bulb bases can be of either screw or bayonet type. Bayonet fittings are common in the United Kingdom while screw fittings are common in the United States of America and other parts of the world.