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Siemens (unit)

Siemens
Unit system SI derived unit
Unit of Electric conductance
Symbol S (= Ω−1) 
Named after Ernst Werner von Siemens
In SI base units: kg−1m−2s3A2

The siemens (SI unit symbol: S) is the unit of electric conductance, electric susceptance and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance, reactance, and impedance respectively; hence one siemens is equal to the reciprocal of one ohm, and is also referred to as the mho. The 14th General Conference on Weights and Measures approved the addition of the siemens as a derived unit in 1971.

The 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); the lower-case "s" is the symbol for the second (unit of time). 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. In English, the same form siemens is used both for the singular and plural.

For a conducting or semiconducting element, electrical resistance R and electrical conductance G are defined as

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

where Ω is the ohm, A is the ampere, and V is the volt.


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