Statampere

The statampere (statA) is the derived electromagnetic unit of electric current in the CGS-ESU (electrostatic cgs) and Gaussian systems of units.[1]:278 One statampere corresponds to 10/ccgs ampere[Note 1] ≈ 3.33564×10−10 ampere in the SI system of units.

statampere
Unit systemCGS-ESU and Gaussian[1]:278
Unit ofelectric current[1]:278
SymbolstatA[1]:278
Named afterA.-M. Ampère
In CGS base unitsg1/2⋅cm3/2⋅s−2 [2]:26
Conversions
1 statA in ...... corresponds to ...
SI base units10/ccgs ampere ≈ 3.33564×10−10 ampere[Note 1][3]:16[2]:26
CGS-EMU1/ccgs abampere ≈3.33564×10−11 abampere[3]:16

The name statampere is a shortening of abstatampere, where the idea was that the prefix abstat should stand for absolute electrostatic and mean ‘belonging to the CGS-ESU (electrostatic cgs) absolute system of units’.[Note 2]

The esu-cgs (or "electrostatic cgs") units are one of several systems of electromagnetic units within the centimetre–gram–second system of units; others include CGS-EMU (or "electrostatic cgs units"), Gaussian units, and Lorentz–Heaviside units. In the cgs-emu system, the unit of electric current is the abampere. The unit of current in the Lorentz–Heaviside system doesn't have a special name.

The other units in the cgs-esu and Gaussian systems related to the statampere are:

  • statcoulomb – the charge that passes in one second through any cross-section of a conductor carrying a steady current of one statampere
  • statvolt – the electrostatic potential difference such that moving a charge of one statcoulomb through it at constant speed requires one erg of work to be done.
  • statohm – the resistance of a conductor that, with a constant current of one statampere through it, maintains between its terminals a potential difference of one statvolt

Notes
  1. The dimensionless constant ccgs = 2.99792458×1010 is numerically equal to the magnitude of the speed of light when the latter is expressed in cm/s.
  2. For quite a long time, the ESU and EMU units didn't have special names; one would just say, e.g. the ESU unit of resistance. It was apparently only in 1903 that A. E. Kennelly suggested that the names of the EMU units be obtained by prefixing the name of the corresponding ‘practical unit' by ‘ab-’ (short for ‘absolute’, giving the ‘abohm’, ‘abvolt’, the ‘abampere’, etc.), and that the names of the ESU units be analogously obtained by using the prefix ‘abstat-’, which was later shortened to ‘stat-’ (giving the ‘statohm’, ‘statvolt’, ‘statampere’, etc.).[4]:534–5 This naming system was widely used in the U.S., but, apparently, not in Europe.[5]

References
  1. Fenna, Donald (2002). A Dictionary of Weights, Measures, and Units. Oxford University Press. ISBN 978-0-19-107898-9.
  2. Gyllenbok, Jan (2018). Encyclopaedia of Historical Metrology, Weights, and Measures: Volume 1. Birkhäuser. ISBN 978-3-319-57598-8.
  3. Cook, James L. (1991). Conversion Factors. Oxford University Press. ISBN 978-0-19-856349-5.
  4. Kennelly, A. E. (July 1903). "Magnetic Units and Other Subjects that Might Occupy Attention at the Next International Electrical Congress". Transactions of the American Institute of Electrical Engineers. XXII: 529–536. doi:10.1109/T-AIEE.1903.4764390. [p. 534] The expedient suggests itself of attaching the prefix ab or abs to a practical or Q. E. S. unit, in order to express the absolute or corresponding C. G. S. magnetic unit. … [p. 535] In a comprehensive system of electromagnetic terminology, the electric C. G. S. units should also be christened. They are sometimes referred to in electrical papers, but always in an apologetic, symbolical fashion, owing to the absence of names to cover their nakedness. They might be denoted by the prefix abstat.
  5. Silsbee, Francis (April–June 1962). "Systems of Electrical Units". Journal of Research of the National Bureau of Standards Section C. 66C (2): 137–183. doi:10.6028/jres.066C.014.
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