electric and magnetic units

electric and magnetic units,

units used to express the magnitudes of various quantities in electricity and magnetism. Three systems of such units, all based on the metric systemmetric system,
system of weights and measures planned in France and adopted there in 1799; it has since been adopted by most of the technologically developed countries of the world.
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, are commonly used. One of these, the mksa-practical system, is defined in terms of the units of the mks systemmks system,
system of units of measurement based on the metric system and having the meter of length, the kilogram of mass, and the second of time as its fundamental units. Other mks units include the newton of force, the joule of work or energy, and the watt of power.
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 and has the ampereampere
, abbr. amp or A, basic unit of electric current. It is the fundamental electrical unit used with the mks system of units of the metric system. The ampere is officially defined as the current in a pair of equally long, parallel, straight wires 1 meter apart that produces
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 of electric current as its basic unit. The units of this system—the volt, ohm, watt, and farad—are those commonly used by scientists and engineers to make practical measurements. The two other systems are both based on the cgs systemcgs system,
system of units of measurement based on the metric system and having the centimeter of length, the gram of mass, and the second of time as its fundamental units. Other cgs units are the dyne of force and the erg of work or energy.
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. Electrostatic units (cgs-esu) are defined in a way that simplifies the description of interactions between static electric charges; there are no corresponding magnetic units in this system. Electromagnetic units (cgs-emu), on the other hand, are defined especially for the description of phenomena associated with moving electric charges, i.e., electric currents and magnetic poles. The two cgs systems have been widely used in the past and are still found in many texts and papers. The official body for maintaining such units in the United States is the National Institute of Standards and Technology.
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