BASIC TERMS AND DEFINITIONS
ATOMS AND ELECTRICITY Our understanding of electricity starts with the ancient Greeks, who used the words “electric force” in describing the mysterious attraction and repulsion exhibited by amber when rubbed with a cloth. The word “electric” is actually from the Greek word for amber. Additional knowledge of the physical structure of matter has allowed modern people to develop today’s electrical and electronic devices. We can best describe the electrical nature of matter by reviewing the structure of elements. An element is a substance that cannot be decomposed to form simpler sub- stances by any chemical means. The smallest portion into which an element can be subdivided without losing its physical and chemical properties is called an atom. The most straightforward concept of the atom is based on a model described by the Danish physicist Niels Bohr (1885-1962) in 1913. This model describes the atom as spherical in shape with a small core or nucleus in the center surrounded by a number of spherical concentric shells. The nucleus contains positively charged particles, protons, and electrically uncharged masses, neutrons. The electrons, negatively charged masses, are distributed in the shells of the atom. The number of electrons and protons are equal, thereby producing overall neutrality. The diameter of a typical metallic atom’s nucleus such as silver is approximately 10,000 times smaller than the whole atom, a point at the center for all practical purposes. Fig. 1.1 shows models of the helium and lithium atoms. The electrons in the outer shell farthest from the nucleus, called the valence electrons, experience a comparatively weak attraction to it. It is the valence electrons that control the electrical and chemical properties of the atom. The valence electrons may wander into outer shells of nearby atoms. Random wandering of outer electrons from one atom to another does not produce any permanent change. If no outside influence disturbs the balance,
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ATOMS AND ELECTRICITY Our understanding of electricity starts with the ancient Greeks, who used the words “electric force” in describing the mysterious attraction and repulsion exhibited by amber when rubbed with a cloth. The word “electric” is actually from the Greek word for amber. Additional knowledge of the physical structure of matter has allowed modern people to develop today’s electrical and electronic devices. We can best describe the electrical nature of matter by reviewing the structure of elements. An element is a substance that cannot be decomposed to form simpler sub- stances by any chemical means. The smallest portion into which an element can be subdivided without losing its physical and chemical properties is called an atom. The most straightforward concept of the atom is based on a model described by the Danish physicist Niels Bohr (1885-1962) in 1913. This model describes the atom as spherical in shape with a small core or nucleus in the center surrounded by a number of spherical concentric shells. The nucleus contains positively charged particles, protons, and electrically uncharged masses, neutrons. The electrons, negatively charged masses, are distributed in the shells of the atom. The number of electrons and protons are equal, thereby producing overall neutrality. The diameter of a typical metallic atom’s nucleus such as silver is approximately 10,000 times smaller than the whole atom, a point at the center for all practical purposes. Fig. 1.1 shows models of the helium and lithium atoms. The electrons in the outer shell farthest from the nucleus, called the valence electrons, experience a comparatively weak attraction to it. It is the valence electrons that control the electrical and chemical properties of the atom. The valence electrons may wander into outer shells of nearby atoms. Random wandering of outer electrons from one atom to another does not produce any permanent change. If no outside influence disturbs the balance,
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