- Siemens (unit)
The siemens (symbol: S) is the SI derived unit of electric conductance and electric admittance. Conductance and admittance are the reciprocals of resistance and impedance respectively, hence one siemens is equal to the reciprocal of one ohm, and is sometimes referred to as the mho. It is named after the German inventor and industrialist Ernst Werner von Siemens. In English, the term siemens is used both for the singular and plural. The 14th General Conference on Weights and Measures approved the addition of the siemens as an SI derived unit in 1971.
This SI unit is named after Ernst Werner von Siemens. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (S). When an SI unit is spelled out in English, it should always begin with a lower case letter (siemens), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units, section 5.2.
where I is the electric current through the object and V is the voltage (electrical potential difference) across the object.
The unit siemens for the conductance G is defined by
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.
Example: The conductance of a resistor with resistance six ohms is G = 1/(6 Ω) ≈ 0.167 S ≈ 167 mS.
Since 1860 to the middle of 20th century, siemens or siemens mercury unit, was the unit of electrical resistance. It was defined as the resistance of a mercury column 1 meter long and uniform 1 mm2 cross sectional area at 0 degrees Celsius. It was equivalent to 0.953 ohm approximately. Officially, it ceased usage after 1881, but was widely used in telegraph and telephone services until World War II.
Mho is an alternate, non-SI unit of conductivity which is equivalent to 1 siemens. Mho is derived from spelling ohm backwards and is written with an upside-down capital Greek letter Omega: , Unicode symbol U+2127 (℧). According to Maver the term mho was suggested by Sir William Thomson. The mho was officially renamed to the siemens, replacing the old meaning of the unit siemens, at a conference in 1881.
The term siemens, as it is an SI unit, is used universally in science and often in electrical applications, while mho is still used primarily in electronic applications. Two reasons are usually given for using mho instead of siemens in electronic applications:
- The inverted Omega and the mho, while not an official SI abbreviation, has the advantage of being less likely to be confused with a variable than the letter S when doing algebraic calculations by hand, where the usual typographical distinctions (such as italic for variables and Roman for unit names) are difficult to maintain. Likewise, it is difficult to distinguish the symbol S from the lower case s where second is meant, potentially causing confusion.
- The term siemens could be confused with the large multinational electronics company Siemens.
- ^ NIST Guide to SI Units - 9 Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology
- ^ Maver, William: American Telegraphy and Encyclopedia of the Telegraph: Systems, Apparatus, Operation. 1903.
- ^ http://www.tech-faq.com/siemens.html
SI units Base units Derived units Accepted for use
See alsoBook:International System of Units · Category:SI base units
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Siemens unit — simensas statusas T sritis automatika atitikmenys: angl. Siemens; Siemens unit vok. Siemens, n rus. сименс, m pranc. siemens, m … Automatikos terminų žodynas
Siemens unit — simensas statusas T sritis fizika atitikmenys: angl. siemens; Siemens unit vok. Siemens, n rus. сименс, m pranc. siemens, m … Fizikos terminų žodynas
Siemens (disambiguation) — Siemens AG is a German electrical and telecommunications companysiemens may refer to *siemens (unit), the SI unit of electrical conductance, equivalent to 1 ampere/voltSiemens may also refer to: *Jake Siemens, a Canadian social entrepreneur and… … Wikipedia
Siemens (unite) — Siemens (unité) Pour les articles homonymes, voir Siemens … Wikipédia en Français
siemens — /see meuhnz/, n. (used with a sing. v.) Elect. the SI unit of electrical conductance, equal to the reciprocal of the ohm and replacing the equivalent MKS unit (mho). Abbr.: S [1930 35; named after Sir W. SIEMENS] * * * (as used in expressions)… … Universalium
Siemens — /see meuhnz/; Ger. /zee meuhns/, n. 1. (Ernst) Werner von /erddnst verdd neuhrdd feuhn/, 1816 92, German inventor and electrical engineer. 2. his brother, Sir William (Karl Wilhelm Siemens), 1823 83, English inventor, born in Germany. * * * (as… … Universalium
Siemens — simensas statusas T sritis automatika atitikmenys: angl. Siemens; Siemens unit vok. Siemens, n rus. сименс, m pranc. siemens, m … Automatikos terminų žodynas
siemens — simensas statusas T sritis automatika atitikmenys: angl. Siemens; Siemens unit vok. Siemens, n rus. сименс, m pranc. siemens, m … Automatikos terminų žodynas
Siemens — simensas statusas T sritis fizika atitikmenys: angl. siemens; Siemens unit vok. Siemens, n rus. сименс, m pranc. siemens, m … Fizikos terminų žodynas
siemens — simensas statusas T sritis fizika atitikmenys: angl. siemens; Siemens unit vok. Siemens, n rus. сименс, m pranc. siemens, m … Fizikos terminų žodynas