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Siemens (unit)
 
 
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The siemens (symbol: S) is the SI
Si

Si, si, or SI may refer to :...
 derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of electric conductance. It is equal to inverse ohm
Ohm

The ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Ohm....
. It is named after the German
Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium, and the Netherlands....
 inventor and industrialist Ernst Werner von Siemens
Ernst Werner von Siemens

Ernst Werner von Siemens was a German inventor and industrialist. Siemens' name has been adopted as the SI unit of electrical conductance, the siemens ....
, and was previously called the mho. In English, the term siemens is used both for the singular and plural. The 14th General Conference on Weights and Measures
General Conference on Weights and Measures

The General Conference on Weights and Measures is the English name of the Conf?rence g?n?rale des poids et mesures . It is one of the three organizations established to maintain the International System of Units under the terms of the Convention du M?tre of 1875....
 approved the addition of the siemens as an SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 in 1971.
a physical object, typically an electronic device, with electrical resistance
Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
 R, the conductance
Electrical conductance

Electrical conductance is a measure of how easily electricity flows along a certain path through an electrical element. The SI derived unit of conductance is the Siemens ....
 G is defined as

where I is the electric current through the object and V is the voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 (electrical potential difference) across the object.

The unit siemens for the conductance G is defined by Note that the last term is in SI base unit
SI base unit

The International System of Units defines seven dimensional analysis SI base units. All other physical units can be derived from these base units: these are known as SI derived units....
s where A is the symbol for ampere
Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
, the unit of electric current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
; kg is the symbol for kilogram
Kilogram

The kilogram or kilogrammeThe spelling kilogram is used by the International Committee for Weights and Measures and the U.S....
, the unit of mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
; m is the symbol for metre
Metre

The metre or meter is a Unit of measurement of length. It is the SI base unit of length in the metric system and in the International System of Units , used around the world for general and scientific purposes....
, the unit of length
Length

Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end....
; and s is the symbol for the time
Time

Time is a component of the measurement used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects....
 unit second
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
.






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The siemens (symbol: S) is the SI
Si

Si, si, or SI may refer to :...
 derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of electric conductance. It is equal to inverse ohm
Ohm

The ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Ohm....
. It is named after the German
Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium, and the Netherlands....
 inventor and industrialist Ernst Werner von Siemens
Ernst Werner von Siemens

Ernst Werner von Siemens was a German inventor and industrialist. Siemens' name has been adopted as the SI unit of electrical conductance, the siemens ....
, and was previously called the mho. In English, the term siemens is used both for the singular and plural. The 14th General Conference on Weights and Measures
General Conference on Weights and Measures

The General Conference on Weights and Measures is the English name of the Conf?rence g?n?rale des poids et mesures . It is one of the three organizations established to maintain the International System of Units under the terms of the Convention du M?tre of 1875....
 approved the addition of the siemens as an SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 in 1971.

Definition


For a physical object, typically an electronic device, with electrical resistance
Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
 R, the conductance
Electrical conductance

Electrical conductance is a measure of how easily electricity flows along a certain path through an electrical element. The SI derived unit of conductance is the Siemens ....
 G is defined as

where I is the electric current through the object and V is the voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 (electrical potential difference) across the object.

The unit siemens for the conductance G is defined by Note that the last term is in SI base unit
SI base unit

The International System of Units defines seven dimensional analysis SI base units. All other physical units can be derived from these base units: these are known as SI derived units....
s where A is the symbol for ampere
Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
, the unit of electric current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
; kg is the symbol for kilogram
Kilogram

The kilogram or kilogrammeThe spelling kilogram is used by the International Committee for Weights and Measures and the U.S....
, the unit of mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
; m is the symbol for metre
Metre

The metre or meter is a Unit of measurement of length. It is the SI base unit of length in the metric system and in the International System of Units , used around the world for general and scientific purposes....
, the unit of length
Length

Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end....
; and s is the symbol for the time
Time

Time is a component of the measurement used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects....
 unit second
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
. C is the symbol for the SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of electric charge
Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields....
, the coulomb; V is the symbol for the SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
, the volt
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
; and O is the symbol for the SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of electrical resistance
Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
, the ohm.

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
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
 of electric potential difference across the device.

Example: The conductance of a resistor with resistance six ohm
Ohm

The ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Ohm....
s is G = 1/(6 O) 0.167 S.

Historical/Deprecated


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 1 mm squared 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
World War II

World War II, or the Second World War , was a global military conflict which involved a Participants in World War II, including all of the great powers, organised into two opposing military alliances: the Allies of World War II and the Axis powers....
.

Mho


The siemens was previously referred to by the term mho, which was derived from spelling ohm backwards and written with an upside-down capital Greek
Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
 letter Omega: , Unicode symbol U+2127 . 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 inverted Omega, 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.

Not to be confused with Mohs scale of mineral hardness
Mohs scale of mineral hardness

Not to be confused with Siemens_#Mho, a unit of electric conductance.The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material....
.