Siemens (unit)
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The siemens (symbol: S) is the SI derived unit of electric conductance. It is named after the German inventor and industrialist Ernst Werner von Siemens.
Definition
For a device with electrical resistance R, the conductance G is defined as
<math>G = \frac1R = \frac{I}V, </math>
where
- G is the conductance,
- R is the resistance,
- I is the current through the device and
- V is the voltage "drop" (electrical potential difference) across the device.
The unit Siemens for the conductance G is defined by 1 S = 1 A/V = 1 A2/W = 1 kg−1·m−2·s3·A2 =1 Ω-1.
Example: The conductance of a resistor with resistance 6 Ohm is G = 1/(6 &Omega); = 0.16... S.
SI multiples
| Multiple | Name | Symbol | Multiple | Name | Symbol | |
|---|---|---|---|---|---|---|
| 100 | siemens | S | ||||
| 101 | decasiemens | daS | 10–1 | decisiemens | dS | |
| 102 | hectosiemens | hS | 10–2 | centisiemens | cS | |
| 103 | kilosiemens | kS | 10–3 | millisiemens | mS | |
| 106 | megasiemens | MS | 10–6 | microsiemens | µS | |
| 109 | gigasiemens | GS | 10–9 | nanosiemens | nS | |
| 1012 | terasiemens | TS | 10–12 | picosiemens | pS | |
| 1015 | petasiemens | PS | 10–15 | femtosiemens | fS | |
| 1018 | exasiemens | ES | 10–18 | attosiemens | aS | |
| 1021 | zettasiemens | ZS | 10–21 | zeptosiemens | zS | |
| 1024 | yottasiemens | YS | 10–24 | yoctosiemens | yS |
"Mho" (obsolete!)
The siemens is equivalent to the now obsolete mho unit, which was derived from spelling ohm backwards and written with an upside-down capital Greek letter Omega: <math>\mho</math>. The term siemens, as it is an SI unit, is used universally in science and primarily in electrical applications, while mho is still used primarily in electronic applications. The upside down ohm symbol, while not an official SI unit, 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.bg:Сименс cs:Siemens da:Siemens (ledningsevneenhed) de:Siemens (Einheit) es:Siemens (unidad) fr:Siemens (unité) he:סימנס ja:ジーメンス (単位) nl:Siemens (eenheid) pl:Simens pt:Siemens (unidade) ru:Сименс (единица измерения) sr:Сименс (јединица)
