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  Electricity - Conductors and Insulators Teacher's Notes  
  When you study high-school chemistry, you'll learn that some types of molecules feel more strongly about their electrons than do other types of molecules. This is a very useful characteristic for electricity and electronics.
Some materials are willing to let a few electrons move from molecule to molecule. Materials that let electrons move through them are called "conductors".
Although some are better than others, most metals are good conductors of electricity. Silver, Gold, and Platinum are good conductors but are expensive, so they are only used when price is not important compared to function. Copper and Aluminum are also good conductors and are fairly inexpensive. Thus the wiring in our houses is copper, and the high voltage electric lines that we see crossing the country use aluminum cables.
Other substances keep their electrons under very tight control. Materials that do not let electrons move through them are called "insulators".
Glass is an example of a type of material that keeps its electrons tightly controlled. Glass is made of silicon molecules, organized very tightly in to crystaline structures. Glass is an extremely good insulator. Many plastics are good insulators too. Plastics are cheap, flexible, and durable. That is why the wiring in our houses is covered with a layer of plastic.

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