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![[image of flower]](../../ima/flowXS_03.gif)
Electromagnetism and Electricity |
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Chronology
Electromagnetism (EM) is the total of the effects of the electromagnetic field, which is composed of an electric field and a magnetic field. Each looks like a sine wave in a plane that is 90° apart from the other. The electric field is caused by stationary electric charges (ions, electrons) that, in turn, produces an electric force that causes other charges to flow, i.e, produces electricity. The magnetic field is produced by the movement (motion) of electric charges (electricity) that produces a magnetic force. Therefore, every moving charge, i.e., electricity, has both an electric field and a magnetic field, each of which produces forces in directions different from each other. Together, these forces are known as the electromotive force, one of the four fundamental forces of the universe. Wiki n.p. (Gravity is the force that attracts one body to another; the strong nuclear force holds the positive charges in an atomic nucleus together; the weak nuclear force causes some atoms to radiate electromagnetic fields, e.g., gamma rays and X-rays.) The everyday gross forces that we encounter, e.g., muscle force used to strike a nail with a hammer are combinations of electromagnetic forces made in the body.) The electromagnetic field consists of an infinite number of waves, each having a particular
frequency and wave length. In total, these waves are
known as the electromagnetic spectrum and (electromagnetic spectrum)
Wiki n.p. where The energies and forces of the electromagnetic spectrum are extremely important to technology and living standards, because they enable us to use batteries, generators, motors, transformers, X-ray photographs, spectroscopes, etc. There are some offsetting disadvantages, however. High-energy EM radiation damages living cells, which can harm and even kill organisms, and they can persist in the environment for a long time at harmful energy levels. Some of the more significant EM waves are discussed below: Gamma Rays have more energy and therefore are more penetrating than either alpha rays or beta rays, although they are less ionizing. Gamma rays are distinguished from X-rays by their origin: Gamma rays are produced by nuclear transitions, i.e., atoms of one element converting into atoms of another element. X-rays are produced by energy transitions of electrons moving from one energy level (orbital) to another energy level within one atom. Because some electron transitions are associated with higher energy than nuclear transitions, there is an overlap between low energy gamma rays and high energy X-rays. Since gamma rays destroy cells, they are dangerous and must be shielded with thick metalic and/or concrete housings. Wiki n.p. Gamma rays are very useful. They are used to kill bacteria and other microorganisms, sterilize medical devices, and change the molecular structure of plastics to modify their properties, e.g., to improve their resistance to heat and abrasion X-rays are similar to gamma rays, the difference being mainly between their sources, and their energies overlap. Both are dangerous to organisms and must be heavily shielded. X-rays are very useful. In medicine, X-ray machines photograph internal organs of a body for diagnoses. The principle of electromagnetic induction links electromagnetic waves to electrical current flowing in a conductor. Whenever EM waves change, they exert a force on electrons in a conductor that causes them to flow. This fact is used to generate electricity in power stations through an electrical generators. Conversely, changing strength of electricity in a conductor causes EM radiation. This fact is used to produce EM radiation used in radios and television. Radio waves are generated by an alternating current generators on which are superimposed information that is fed to a transmitting radio antenna. The antenna creates an electrical field that is picked up by a receiver antenna that in turn produces an electrical current containing the same information. A history of electromagnetism discoveries is given below. To 1790 Static electric charge was known and studied since ancient times, but it had no practical use. The ancients knew that rubbing materials together produced attractive forces, e.g., when amber is rubbed, it attracts several materials. In 1660, the German physicist, Otto von Guericke (who also invented the air pump) made a globe of sulfur that was rotated on a crankshaft. When it was stroked by the hand, it accumulated static electric charge. Sparks could be produced with this globe. In 1706, the English physicist, Francis Hauksbeem used a glass sphere on a crankshaft, which built up a much larger static electric charge than the sulfur globe. This experiment stimulated other scientists to study electricity. In 1729, Stephen Gray, an Englishman, produced an electric charge along a glass tube, which charged two corks placed at its ends. This indicated that the charge traveled from the tube to the corks. Experimenting with different substances, he found that the electric charge traveled in some substances, but not in others. This led to the division of substances between conductors and nonconductors (insulators). This flowing charge was then called an electric fluid, what was later called electrical conductance, electric current, or simply electricity. Asimov 172,203 In 1733, the French physicist, Charles-François de Cisternay du Fay found that two pieces of cork charged by the same material repelled each other, while if one cork was charged by a glass rod and the other by a charged resin rod, the two corks attracted each other. Du Fray decided, erroneously, that there must be two electrical fluids, vitreous (glass) electricity and resinous electricity. Asimov 213 The glass sphere (see above) was replaced by the smaller and more practical Leyden jar as an electrical charge storage device in 1746. It was named after Leyden, Netherlands, where its inventor, Pieter van Musschenbroek, worked as a physicist at the Univ. of Leiden. It was also called a "condenser" because scientists at the time thought that electricity was something that could be condensed. Today, it is called a capacitor. There are many types of Leyden jars (they are popular science demonstration projects), but the original one consisted of a container partially filled with water and electrically insulated from its surroundings by suspending it from insulating silk cords. A thick wire is placed through an insulating cork covering the container opening near, but not into, the water. The wire is charged with a friction device brought in contact with it. When the charge reaches becomes too great for the insulating air between the wire and water, it discharges as an electric current (a "spark"); that is, electricity. The German physicist, Ewald Georg von Kleist, invented the same device in 1745, but he did not popularize whatever experiments he made with it. Sometime later, William Watson, an English physician and scientist, constructed a more efficient Leyden jar by coating the inside and outside of the container with metal foil to improve its capacity to store charge. The charge discharged when a metal rod was brought in contact with the outside of the container and near the protruding rod at the top. In 1747, he transmitted a spark from his jar through a wire strung across the ThamesRiver. In 1747, Benjamin Franklin, who also experimented with the Leyden jar and rejected du Fay's theory of two kinds of electricity, vitreous and resinous. He suggested one kind of electricity, which would be in excess, which he called positive electricity, and deficit, which he called negative electricity. The Leyden Jar was similar to the lightning stroke, which also emitted a spark and sound when electricity was discharged. This led to his famous (but extremely dangerous, so don't try it) kite-flying experiment in Bucks County, PA, in 1751, which confirmed that a lightning bolt was also electricity. Later, he charged the Leyden jar with a lightning bolt to further confirm that both electricities were the same. These experiments led to Franklin's invention of the lightning rod in 1752, which eventually was adopted throughout Europe and America. Asimov 226 This invention was the first practical application of natural electricity, a lightning bolt, but there were no applications of machine-created electricity that could be used until 1800, when Alessandro Volta invented the battery. Electromagnetic induction was discovered in 1831 by Michael Faraday and Joseph Henry independently. This principle would later result in the invention of electrical generators, motors, transformers, radios, televisions, computers in the Age of Electricity. |
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