materia : all matter in made up atoms. atoms have nucleus with electrons in motion around it. the nucleus is composed of protons and neutrons (not shown). electrons have negative charge (-) protons have a positive charge (+). Neutrons are neutral. in the normal state of an atom, the number of electrons is equal to the number of protons and the negative charge of the electrons is balanced by the positive charge of the protons. electrons move about the nucleus at the different distances. The closer to the nucleus, the more tightly bound the electrons are to the atom. electrons in the outer band can be easily force out of the atom by the application of some external force such as a magnetic field, friction, or chemical action. electrons forced from atoms are sometimes called free electrons. A free electron leaves a viod which can be filled by an eletron force out of another atom. an electric current is produced when free electrons move from atom to atom in a material. materials that permit many electrons to move freely are called conductors.copper, silver, gold, aluminum, zinc, brass, and iron are considered good conductors. Of these materials, copper and aluminum are most commonly used as conductors. materials that allow few free electrons are called insulators. Materials such as plastic, rubber, glass, mica, and ceramic are good insulators. an electric cable is oneexample of how conductors and insulators are used. Electrons flow along a copper or aluminum conductor to provide energy to an electric divece such as a radio, lamp, or a motor. An insulator around the outside of the copper conductor is provided to keep electrons in the conductor Semiconductor materials, such as silicon, can be used to manufacture diveces that have characteristics of both conductors and
Posted on: Tue, 27 Aug 2013 21:53:36 +0000
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