# Electricity

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Electricity, phenomenon of charged subatomic particles at rest or in motion. Electricity provides a highly versatile form of energy. Electric charge is an inherent property of matter. Electrons carry a negative charge and protons carry a positive charge. For each electron in the atom, there is normally 1 proton. When this balance is disturbed, a net charge is left on an object; the study of such isolated charges is called electrostatics. Like charges repel and unlike charges attract each other with a force proportional to the 2 charges and inversely proportional to the square of the distance between them (the inverse-square law). This force is normally interpreted in terms of an electric field produced by one charge with which the other interacts. Pairs of equal but opposite charges separated by a small distance are called dipoles; the product of charge and separation is called the dipole moment. The amount of work done in moving a unit charge from one point to another against the electric field is called the electric potential difference, or voltage, between the points; it is measured in volts. The ratio of a charge added to a body to the voltage produced is called the capacitance of the body. The presence of an electric field in a conductor produces a steady flow of charge in the direction of the field; such a flow constitutes an electric current, measured in amperes. Electric sources such as batteries and generators convert chemical, mechanical, or other energy into electrical energy and pump charge through conductors much as a water pump circulates water in a radiator heating system. Batteries create a constant voltage, producing a steady, or direct, current (DC). Many generators, on the other hand, provide a voltage that changes in direction many times a second and so produces an alternating current (AC), in which the charges move to and fro instead of continuously in one direction. The latter system has advantages in generation, transmission, and application and is now used almost universally for domestic and industrial purposes. Static electricity was known to the ancient Greeks. The 18th century saw the initiation of many experiments with conduction and other aspects of electricity. The inverse square law was hinted at by J. Priestley in 1767 and later confirmed by H. Cavendish and C.A. Coulomb. G.S. Ohm formulated his law of conduction in 1826, although its essentials were known before then. The common nature of all the “types” of electricity then known was demonstrated in 1826 by M. Faraday, who also originated the concept of electric field lines.

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