The unit is named afterErnst Werner von Siemens. In English, the same wordsiemens is used both for the singular and plural.[3] Like other SI units named after people, the name of the unit (siemens) is not capitalized. Its symbol (S), however,is capitalized to distinguish it from thesecond, whose symbol (s) is lower case.
The related property,electrical conductivity, is measured in units of siemens per metre (S/m).
For a device with a conductance of one siemens, the electric current through the device will increase by one ampere for every increase of one volt of electric potential difference across the device.
The conductance of a resistor with a resistance of five ohms, for example, is (5 Ω)−1, which is equal to a conductance of 200 mS.
A historical equivalent for thesiemens is themho (/ˈmoʊ/). The name is derived from the wordohm spelled backwards as the reciprocal of one ohm, at the suggestion ofSir William Thomson (Lord Kelvin) in 1883.[4] Its symbol is an upside-down capitalGreek letteromega.
NIST'sGuide for the Use of the International System of Units (SI) refers to the mho as an "unaccepted special name for an SI unit", and indicates that it should be strictly avoided.[5][clarification needed]
The SI termsiemens is used universally in science and often in electrical applications, whilemho is still used in some electronic contexts.[6][7]
The upside-down capital omega symbol (℧), while not an official SI abbreviation, is less likely to be confused with a variable than the letter "S" when writing the symbol by hand. The usual typographical distinctions (such as italic for variables and roman for units) are difficult to maintain. Likewise, it is difficult to distinguish the symbol "S" (siemens) from the lower-case "s" (seconds), potentially causing confusion.[8] So, for example, apentode’stransconductance of2.2 mS might alternatively be written as2.2 m℧ or2200 μ℧ (most common in the 1930s) or2.2 mA/V.
Theohm had officially replaced theold "siemens unit", a unit ofresistance, at an international conference in 1881.[9]
^Thomson, William (1884)."Electrical Units of Measurement".The Practical Applications of Electricity. Institution of Civil Engineers. pp. 149–174 at p 171 (Lecture given 3 May 1883). Available online. Thomson helpfully added that the proper pronunciation of "mho" could be obtained by taking a phonograph and turning it backwards.
^"Chapter 5: Units Outside the SI". NIST Guide to the SI (Report). National Institute of Standards and Technology. 2008. Retrieved2017-12-22.
^Al Dahaan, S., Al-Ansari, N., & Knutsson, S. (2016). Influence of groundwater hypothetical salts on electrical conductivity total dissolved solids. Engineering, 8(11), 823-830.
^SINGH, S., GAUTAM, P. K., KUMAR, P., BISWAS, A., & SARKAR, T. (2021). Delineating the characteristics of saline water intrusion in the coastal aquifers of Tamil Nadu, India by analysing the Dar-Zarrouk parameters. Contributions to Geophysics & Geodesy, 51(2).
^Weiner, Eugene R. (2013).Applications of Environmental Aquatic Chemistry: A practical guide. CRC Press. p. 109.ISBN978-1439853320.
