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The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. It is defined as the fraction 1/273.16 of the thermodynamic (absolute) temperature of the triple point of water.
A temperature given in kelvins, without further qualification, is measured with respect to absolute zero, where molecular motion stops (except for the residual quantum mechanical zero-point energy). It is also common to give a temperature relative to the Celsius temperature scale, with a reference temperature of 0 °C = 273.15 K, approximately the melting point of water under ordinary conditions.
The kelvin is named after the British physicist and engineer William Thomson, 1st Baron Kelvin; his barony was in turn named after the River Kelvin, which runs through the grounds of the University of Glasgow.
Typographical conventions
The word "kelvin" as an SI unit is correctly written with a lowercase k (unless at the beginning of a sentence), and is never preceded by the words degree or degrees, or the symbol °, unlike degrees Fahrenheit, or degrees Celsius. This is because the latter are adjectives, whereas kelvin is a noun. It takes the normal plural form by adding an s in English: kelvins. When the kelvin was introduced in 1954 (10th General Conference on Weights and Measures (CGPM), Resolution 3, CR 79), it was the "degree Kelvin", and written °K; the "degree" and the uppercase K was dropped in 1967 (13th CGPM, Resolution 3, CR 104). Of course, the temperature scale is the Kelvin (adjective) scale.
Note that the symbol (not abbreviation) for the unit kelvin is always a capital K and never italicised. There is a space between the number and the K, as with all other SI units.
Unicode includes the "kelvin sign" at U+212A (in your browser it looks like K). However, the "kelvin sign" is canonically decomposed into U+004B, thereby seen as a (preexisting) encoding mistake, and it is better to use U+004B (K) directly.
Conversion factors
Kelvins and Celsius
The Celsius temperature scale is now defined in terms of the kelvin, with 0 °C corresponding to 273.15 kelvins.
- kelvins to degrees Celsius
- C = K − 273.15
Kelvins and electronvolts
In some fields, plasma physics in particular, the electronvolt (eV) is used as a unit of 'temperature'. The conversion makes use of k, the Boltzmann constant.
SI multiples
| Multiple |
Name |
Symbol |
|
Multiple |
Name |
Symbol |
| 100 |
kelvin |
K |
|
|
|
|
| 101 |
decakelvin |
daK |
|
10–1 |
decikelvin |
dK |
| 102 |
hectokelvin |
hK |
|
10–2 |
centikelvin |
cK |
| 103 |
kilokelvin |
kK |
|
10–3 |
millikelvin |
mK |
| 106 |
megakelvin |
MK |
|
10–6 |
microkelvin |
µK |
| 109 |
gigakelvin |
GK |
|
10–9 |
nanokelvin |
nK |
| 1012 |
terakelvin |
TK |
|
10–12 |
picokelvin |
pK |
| 1015 |
petakelvin |
PK |
|
10–15 |
femtokelvin |
fK |
| 1018 |
exakelvin |
EK |
|
10–18 |
attokelvin |
aK |
| 1021 |
zettakelvin |
ZK |
|
10–21 |
zeptokelvin |
zK |
| 1024 |
yottakelvin |
YK |
|
10–24 |
yoctokelvin |
yK |
|
|
This SI unit is named after William Thomson, 1st Baron Kelvin. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (K). But when an SI unit is spelled out, it should always be written in lowercase (kelvin), unless it begins a sentence or is the name "degree Celsius".
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See also
- ITS-90 International Temperature Scale
References
The content of this page is retrieved from http://en.wikipedia.org/wiki/Kelvin under GFDL
