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 system, are commonly used. One of these, the mksa-practical
system, is defined in terms of the units of the mks system and has the ampere 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 system. 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.
source: The Columbia Encyclopedia, Sixth Edition. 2001.