 communi- cations. Analogies to assist in the understanding of a concept are used where appropriate. We cannot see electricity. We can feel its effects such as electrical shock, the generation of heat, and the buildup and decay of magnetic and electrical fields. For example, a compass will indicate the presence of a magnetic field. It is assumed that the reader has had at least three years of high school mathematics including algebra, trigonometry, and logarithms. For those who feel that their background in mathematics is insufficient, Appendix B gives an overview of those basic essentials. A.2 WHAT IS ELECTRICITY? We define electricity as the movement of electrons through a conductor. 1 Certain sub- stances are good conductors and other substances are poor conductors. Poor conductors are called insulators. The various materials or substances we have here on earth run the gamut, from superb conductors such as platinum, gold, silver, and copper to extremely good insulators such as glass, mica, polystyrene, and rubber. The movement of electrons through a conductor is measured in amperes. 2 In fact ampere is the flow of 6.24 X 1018 electrons per second past a given point in a conductor. 1 Encyclopedia Brittanica defines electricity as "The phenomenon associated with positively and negatively charged particles of matter at rest and in motion, individually or in great numbers." 2 An ampere is a unit of electrical measurement. All units of electrical measurement are named for scientists credited with discovering the particular phenomenon, and often providing a mathematical analysis of that electrical phenomenon. Ampere is one example. Fundamentals of Telecommunications, Second Edition, by Roger L. Freeman ISBN 0-471-71045-8 Copyright © 2005 by Roger L. Freeman REVIEW OF FUNDAMENTALS OF ELECTRICITY WITH TELECOMMUNICATION APPLICATIONS Where the flow of electrons is continuous in one direction is called direct current (dc). The currents of electrons may also periodically reverse their flow. This is called alternating curr