绝对温度（absolutetemperature）概念
热力学温度又称开尔文温度T,或称绝对温度,度量符号为K.
绝对零度时的温度定义为0K.冰水混合物的温度为摄氏0度,定义为273.15K.
水在标准大气压下结冰的温度,即摄氏温度0℃,或华氏温度32℉,相当于热力学温度273.16K
绝对温度的原理
一定质量的气体等压膨胀时,在常温下其V－t图线为一条不过坐标原点的直线（盖－吕萨克定律）.若实验测得这条图线,加以外推,出图线与t轴的交点处的摄氏温度值,它就是使理想气体体积变为零的最低温度,即热力学温度（绝对温度）的零度.
绝对零度是一个「理论值」,而非一个实际已经观测到或达到的温度,也就是说,它是一个科学家根据实验所间接「推论」出来的数值；而到目前为止,以人类的科学技术,还达不到这样的低温.
物质的分子无时无刻不在剧烈地运动,也正是因为分子运动的结果,而使得温度上升,因此被称
之为「热运动」；相对地,如果把温度不断地降低,就会使得分子的热运动愈来愈慢、愈来愈慢；那究竟要到什么时候,物质分子才会完全静止不动呢?
绝对零度（也就是大约摄-273.15℃）正是科学家们推导出来的答案；它代表著在此温度之下,物质分子不再具有任何能量来进行热运动,也就是一切的分子都会停止活动.但后来的科学家发现,即使在绝对零度的低温下,分子运动却可能不会完全静止,不过,这已是量子力学的艰深范畴了!
冷冻后的原子温度到底是多少度,方法之一是先把雷射关掉.在朱棣文最初的实验里,原子冷冻后会在这个状态下维持约0.1毫秒(1ms =10-3 s),随后原子就在无动力的情况下离开观测区继续飞行.测量这个只受重力下飞行一段固定距离所需的时间,可以大约估计原子的温度.朱棣文量得的温度大约是 240μK,这大约等于钠原子速度为 30 cm/s的温度,跟理论上计算的多普勒极限差不多,用多普勒冷冻最低就只能达到这个温度了.
The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero kelvin (0 K). The Kelvin scale a
nd the kelvin are named after the British physicist and engineer William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the need for an "absolute thermometric scale". Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to as a "degree", nor is it typeset with a degree symbol; that is, it is written K and not °K.
Contents [hide]
1 History
2 Usage conventions
2.1 Use in conjunction with Celsius
3 Color temperature
4 Kelvin as a measure of noise
5 See also
6 References
7 External links
[edit] History
absolute relativeSee also: thermodynamic temperature#History
1848
Lord Kelvin (William Thomson), wrote in his paper, On an Absolute Thermometric Scale, of the need for a scale whereby "infinite cold" (absolute zero) was the scale’s null point, and which used the degree Celsius for its unit increment. Thomson calculated that absolute zero was equivalent to ?273 °C on the air thermometers of the time.[1] This absolute scale is known today as the Kelvin thermodynamic temperature scale. It’s noteworthy that Thomson’s value of "?273" was actually derived from 0.00366, which was the accepted expansion coefficient of gas per degree Celsius relative to the ice point. The inverse of ?0.00366 expressed to five significant digits is ?273.22 °C which is remarkably close to the true value of ?273.15 °C.
1954
Resolution 3 of the 10th CGPM gave the Kelvin scale its modern definition by designating the triple point of water as its second defining point and assigned its temperature to exactly "273.16 degrees Kelvin."[2]
1967/1968
Resolution 3 of the 13th CGPM renamed the unit increment of thermodynamic temperature "kelvin", symbol K, replacing "degree absolute", symbol °K.[3] Furthermore, feeling it useful to more explicitly define the magnitude of the unit increment, the 13th CGPM also held in Resolution 4 that "The kelvin, unit of thermodynamic temperature, is equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water."[4]
2005
The Comité International des Poids et Mesures (CIPM), a committee of the CGPM, affirm
ed that for the purposes of delineating the temperature of the triple point of water, the definition of the Kelvin thermodynamic temperature scale would refer to water having an isotopic composition specified as VSMOW.[5]
[edit] Usage conventions
When reference is made to the unit kelvin (either a specific temperature or a temperature interval), kelvin is always spelled with a lowercase k unless it is the first word in a sentence.[6] When reference is made to the "Kelvin scale", the word "kelvin"—which is normally a noun—functions adjectivally to modify the noun "scale" and is capitalized.
Until the 13th General Conference on Weights and Measures (CGPM) in 1967–1968, the unit kelvin was called a "degree", the same as with the other temperature scales at the time. It was distinguished from the other scales with either the adjective suffix "Kelvin" ("degree Kelvin") or with "absolute" ("degree absolute") and its symbol was °K. The latter (degree absolute), which was the unit’s official name from 1948 until 1954, was rather ambiguous since it could also be interpreted as referring to the Rankine scale. Before the
13th CGPM, the plural form was "degrees absolute". The 13th CGPM changed the name to simply "kelvin" (symbol K).[7] The omission of "degree" indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales, but rather an absolute unit of measure which can be manipulated algebraically (e.g., multiplied by two to indicate twice the amount of "mean energy" available among elementary degrees of freedom of the system).
This SI unit is named after William Thomson, 1st Baron Kelvin. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is uppercase (K). When an SI unit is spelled out in English, it should always begin with a lowercase letter (kelvin), 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.
The kelvin symbol is always a roman, non-italic capital K. In the SI naming convention, all
symbols named after a person are capitalized; in the case of the kelvin, capitalizing also distinguishes the symbol from the SI prefix "kilo", which has the lowercase k as its symbol. The admonition against italicizing the symbol K applies to all SI unit symbols; only symbols for variables and constants (e.g., P = pressure, and c = 299,792,458 m/s) are italicized in scientific and engineering papers. As with most other SI unit symbols (angle symbols, e.g. 45° 3′ 4〃, are the exception) there is a space between the numeric value and the kelvin symbol (e.g. "99.987 K").[8][9]

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