“ELECTROMAGNETICS” IS at the heart of everything that is done with electricity. It concerns itself with the forces that charge particles exert upon each other. Electromagnetics is a word that was coined in the late 1800s to denote a newly discovered phenomenon that was the combination of what previously had been thought to be completely separate phenomena: electricity and magnetism.
The effects of electric charge have been known since 600 B.C. History records that the ancient Greeks discovered that Amber, a hard, translucent resin, attracted bits of material after it was rubbed with fur. Nearly 2,000 years passed before William Gilbert realized in the early 1600s that this same effect could be observed when rubbing a variety of substances together. It was he who coined the term “electric” using the Greek word for Amber, “elecktron”. In 1660, Otto Von Guericke invented a machine that produced static electricity and Robert Boyle discovered in 1675 that electric force could be transmitted through vacuum and observed attraction and repulsion. The first indication that electricity can move from one place to another came from experiments conducted by Stephen Gray in 1729. He found that when two objects were connected by a tube, both could be electrified when only one was rubbed. In 1733, Charles Francois du Fay discovered that electricity comes into two forms, which he called resinous (-) and vitreous (+). Benjamin Franklin and Ebenezer Kinnersley later renamed the two forms as positive and negative. This discovery (of Stephen Gray) led J.T. Desaguliers in 1739 to the discovery of a class of materials called “Conductors” that pass electricity easily. In 1745, a Dutch physicist, Pieter Van Muschenbroek invented the “Leyden Jar” the first electrical capacitor used to store static electricity and in 1747 William Watson discharged it through a circuit that began the comprehension of current and circuit.
In 1750, John Michel theorized that permanent magnet has north and south poles that attract or repel each other according to an inverse-square law that is similar to Coulomb’s law of force. In 1752, Ben Franklin conducted his famous kite experiment. He invented lighting rods and sold them throughout colonial America. The first quantitative theories of magnetism were advanced in the 18th century. In the year 1800, Volta developed the first chemical battery, which consisted of strips of dissimilar metals immersed in a weak electrolyte. The first evidence that electric and magnet phenomena are related came from Hans Christian Orested, who, in 1819, discovered that a steady current could move a compass needle, just as a permanent magnet can. This was closely followed by Andre-Marie Ampere’s discovery that electric currents exert attractive and repulsive forces on each other. In 1820, D.F. Arago invented the electromagnet. One of the most important series of experiments was performed by George Simon Ohm in 1826; he showed that when a constant voltage is applied to a conductor, the resulting current is proportional to the conductor’s cross-sectional area and inversely proportional to its length. Another important experimental connection between electric and magnetic effects was discovered by Michael Faraday in 1831. He conducted an experiment whereby two insulated wires were wrapped around an iron core and found that when the current in one winding was switched, a voltage was induced in the other and finally developed Transformer. In 1837, Samuel Morse invented the telegraph and in 1858, transoceanic telegraph cable was laid.
With the discovery of Faraday’s law, the stage was setfor the development of a complete theory of Electromagnetism. This was accomplished by James Clerk Maxwell, a professor of experimental physics at Cambridge University. In 1873 he published “A Treatise on Electricity and Magnetism”. In this work, he proposed that just as time-varying magnetic fields can produce electric fields, the opposite is also true. Adding this conjecture to what was already known about electricity and magnetism, Maxwell produced his now-famous system of equations called Maxwell’s equations. In 1876, Alexander Graham Bell invented the telephone and in 1879, Thomas Alva Edison invented the light bulb. Edison directed the operation of the first central commercial incandescent electric generating station in the country. In 1882, it provided electricity to one square mile in New York City. The definitive experimental verification of Maxwell’s theory came in 1886 through a series of experiments conducted by Heinrich Hertz. He discovered Electromagnetic wave in 1888.
The most dramatic application of the new Electromagnetic theory came in 1901 when Guglielmo Marconi sent the first wireless telegraph signals across the Atlantic Ocean. The next two decades saw a host of developments in antennas, amplifying devices, and modulation techniques, culminating in the first commercial radio broadcasting in the early 1920s. Television soon followed in the early 1930s, followed by the radar in the late 1930s. Wireless communication is probably the most conspicuous application of Electromagnetics, since it involves the propagation of Electromagnetic waves through air or space. Nevertheless, Maxwell’s Electromagnetic theory has been equally important in the development of a host of other engineering applications. Other devices and systems in whose development electromagnetic theory played an important part include the vacuum tube (1906), the magnetron (1940), the transistor (1950), the laser (1960), and fiber-optic systems (late 1970s). Starting with the operation of TAT-8 in 1988 (8th transatlantic telephone cable), there is widespread adoption of systems based on Fiber optics from 1990. In fact, it is safe to say that Electromagnetic theory has been an essential ingredient in the development of every electrical device or system that we now take for granted.
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