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/c_cgs ampere^{[Note 1]} ≈ 3.33564×10⁻¹⁰ ampere in the SI system of units.

statampere
Unit system	CGS-ESU and Gaussian[1]:278
Unit of	electric current[1]:278
Symbol	statA[1]:278
Named after	A.-M. Ampère
In CGS base units	g1/2⋅cm3/2⋅s−2 [2]:26
Conversions
1 statA in ...	... corresponds to ...
SI base units	10/ccgs ampere ≈ 3.33564×10−10 ampere[Note 1][3]:16[2]:26
CGS-EMU	1/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 "electromagnetic cgs units"), Gaussian units, and Heaviside–Lorentz units. In the cgs-emu system, the unit of electric current is the abampere. The unit of current in the Heaviside–Lorentz 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 c_cgs = 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]