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  Electricity (from Greek electron, ‘amber’; the rubbing of which causes electrostatic phenomena: see below) is the generic term used to describe the science of electrical conduction, attraction and repulsion, electromagnetics and other electrical phenomena. Although electrical sparks were being studied as early as the 1700s, electricity as a major science has only been under way for just over a century. In this relatively short time electricity utilization has spread epidemically.

The earliest known reference to an electrical phenomenon was to that of electrical attraction by the ancient Greeks, who noted that a piece of amber when rubbed would attract light objects such as leaves or straw. The Greeks believed that amber contained some magical power by which it attracted objects and it was not until the 17th century that a more scientific explanation was produced. In 1600, William Gilbert published a paper giving details about magnetism and electrical attraction. Later, in 1670, a German, Otto Van Guericke, charged a sulphur ball causing electrical sparks to be produced and verifying that opposite charges attract. In 1729, Stephen Gray discovered that the charge could be transferred from one body to another by connecting it with a conductor, usually metallic, but could not be transferred when using an insulated connection, usually non-metallic. Thus electric conduction was discovered.

Up to this time, the only source of electricity was the friction generator, where a body was rubbed to produce an electrical charge on it. However, in 1800 Alessandro Volta invented the battery, a source of electricity that did not require more rubbing to recharge. The battery produced electricity by chemical action between two metals and a liquid. Volta also noted that by stacking the batteries he could produce enough electric charge to cause sparks. The battery also enabled a continuous electric current to flow, compared with the momentary currents produced when friction generators discharged. An electric current was determined to be the movement of charge analogous to the flow of water in a pipe, and electric voltage was considered the ‘pressure’ required to cause the current to flow.

The advent of continuous current sources enabled measurement of electric current and voltage, and led to the circuit theory of today. The first step was Ohm\'s Law which related the current and voltage to the resistance of the conductor. In 1820, Hans Oersted discovered that an electric current produced a magnetic field and in 1831, Michael Faraday showed that a magnetic field can produce an electric current. This was the beginning of electromagnetism, which united the previously separate theories of electrical and magnetic phenomena.

Practical applications for electricity soon began. The incandescent light bulb had been produced by Thomas Edison and the beginnings of an electric power network to supply the new electric street lamps was under way by the 1880s. Electric telegraphy was started around the 1840s and the following introduction of the telephone in the late 1870s heralded the start of the modern communications era.

The theory of electricity progressed rapidly during the 19th century and culminated with James Maxwell\'s electromagnetic theory. This theory, among other ideas, predicted that electricity could be transmitted without the use of wires. This so called ‘wireless electricity’ was shown to exist by Heinrich Hertz in Germany, and is now known as radio.

However advanced the theory had become by this time, there were still several observable electrical effects that the theories could neither explain nor predict. This was to alter following the discovery of the electron by J.J. Thomson in 1897, and the classification of the electron as a fundamental charged particle. The electron was shown to be negatively charged and an electric current was subsequently thought of as being electrons in motion through a conductor. After this discovery, electronic devices which used the properties of the electron appeared in rapid succession, such as the diode and a later derivative the triode.

The discovery of the electron produced great changes in the way human beings studied the materials and interactions of the materials they knew of. The realization that quantum theory provided an explanation of those phenomena where classical theory failed, hastened the age of quantum mechanics and with it the semiconductor age (see semiconductor device theory). Semiconducting materials were shown to have unique electrical properties and in particular allowed the manufacture of reliable electronic devices, such as the transistor.

Transistors and other electronic devices marked the beginning of the computer age, as digital logic circuits were made which could perform arithmetic functions or make simple decisions. The first electronic calculators were produced around the time of World War II, and following the invention of integrated circuit techniques, producing silicon ‘chips’, the first microcomputer was produced in the mid-1970s. AC



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