Conductors and Insulators

Conductors and Insulators

Metals are good conductors (poor insulators). Electrons in the outer layers of metal atoms are free to move from atom to atom. So if one end of a piece of metal is made positive, the electrons will be attracted towards it and because they are free, they can move towards it.

Static charge only builds up on insulators. These are materials that will not allow the flow of charged particles (nearly always electrons) through them. Insulators are materials made from atoms that hold onto their electrons very strongly. The voltage across an insulator has to be extremely high before an electron is given enough energy to free itself and move through the material.

Static charge won't build up on conductors unless they are isolated because as soon as you put too many electrons in one place, they repel each other and spread out, reducing or eliminating the effect. On insulators, the charge can't spread out - so you get a noticeable effect.

You can give metal objects static charge as long as the whole object is insulated from the rest of the world so that charge cannot escape from it (even though the charge is spread evenly throughout the whole metal object).

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Good examples are the metal dome on a Van de Graaff generator and the annoying shocks that you get from cars.

Semi-conductors have far fewer free electrons than metals so do not conduct as well. However, if they are given energy electrons are able to free themselves from their atom and flow, which increases their ability to conduct. Some semi-conductors are light sensitive, as the light energy is able to free the electrons. There are about 5 naturally occurring semi-conductors.

Although in circuits we deal with electrons carrying charge, in liquids and gases other particles are also able to carry charge, such as ions in the process of electrolysis.