A young caller wanted to know why rubber is an insulator. According to Wattenburg, most metals are conductors of electricity, and materials that have a metal-like structure are usually conductive.
The main property shared by conductors is that the atoms that make up the material have some loose electrons on the outside (called conduction bands); where the electrons can move from one atom to the next. Electrical current is the movement of electrons in a conductor. If a material lacks these free electrons (also called conducting electrons)—as rubber does—it will not conduct electricity and is called an insulator.
There are also in-between materials, called semi-conductors, which behave as a conductor or insulator, depending on the amount of voltage applied to the material. This enables such materials to behave as switches and other simple electrical components.
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