出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/11/18 22:32:45」(JST)
| この項目では、温度の単位について記述しています。名前の由来となった人物（ケルヴィン卿）については「ウィリアム・トムソン」をご覧ください。 |
| ケルビン 英 kelvin |
|
|---|---|
| 記号 | K |
| 系 | 国際単位系 (SI) |
| 種類 | 基本単位 |
| 量 | 温度 |
| 定義 | 水の三重点の熱力学温度の273.16分の1 |
| 由来 | 水の標準大気圧下での融点と沸点の温度差の100分の1 |
| 語源 | ケルヴィン卿 |
| テンプレートを表示 | |
ケルビン（kelvin、記号 K）は、熱力学温度（絶対温度）を表す単位。国際単位系の基本単位の一つ。
ケルビンは、古典力学において全ての分子の運動が停止する絶対零度を 0 ケルビン(K)とし、1 ケルビンを水の三重点の熱力学温度（0.01℃）の 1/273.16 倍としている。これは、元々はセルシウス度の値から273.15を減じた（絶対零度を0とした）温度目盛りとして定義されたものであったが、現在では逆にセルシウス度がケルビンを元に定義されている。2005年の国際度量衡委員会(CIPM)の会議において、以下のように補足された。
ケルビンの名はイギリスの物理学者 、ウィリアム・トムソン（後に男爵、ケルヴィン卿となった）にちなんで付けられた。研究生活を送ったグラスゴーにあるケルビン川から取られている。
ケルビンは国際単位系の単位であり、単位記号は大文字の「K」で書き出すのが正しい。「度」や「°」を付けることは無い。「度」は測定の尺度であり、「ケルビン」は測定の単位であることを表している。ただし、1967年の第13回国際度量衡総会まではケルビン度 (°K) が使用されていた。
また、ケルビンは色温度の単位としても用いられる。
セルシウス度（摂氏） t[℃] とケルビン T[K] の関係
華氏 とケルビン K の関係
電子ボルト eV とケルビンの関係
| ケルビン | セルシウス度 | ファーレンハイト度 | ランキン度 | ドリール度 | ニュートン度 | レオミュール度 | レーマー度 | ||
|---|---|---|---|---|---|---|---|---|---|
| 絶対零度 | 0 | −273.15 | −459.67 | 0 | 559.725 | −90.14 | −218.52 | −135.90 | |
| 地球表面の最低気温（※1） | 184 | −89 | −128.2 | 331.47 | 283.5 | −29.37 | −71.2 | −39.225 | |
| ファーレンハイトの寒剤 | 255.37 | −17.78 | 0 | 459.67 | 176.67 | −5.87 | −14.22 | −1.83 | |
| 水の融点（標準状態下） | 273.15 | 0 | 32 | 491.67 | 150 | 0 | 0 | 7.5 | |
| 地球表面の平均気温 | 288 | 15 | 59 | 518.67 | 127.5 | 4.95 | 12 | 15.375 | |
| 人間の平均体温 | 309.95 | 36.8 | 98.24 | 557.91 | 94.8 | 12.144 | 29.44 | 26.82 | |
| 地球表面の最高気温 | （※2） （※3） |
331.95 331 |
58.8 58 |
137.8 136.4 |
597.47 596.07 |
61.8 63 |
19.404 19.14 |
47.04 46.4 |
38.37 37.95 |
| 水の沸点（標準状態下） | 373.15 | 100 | 212 | 671.67 | 0 | 33 | 80 | 60 | |
| チタンの融点 | 1941 | 1668 | 3034 | 3494 | −2352 | 550 | 1334 | 883 | |
| 太陽の表面温度 | 5800 | 5526 | 9980 | 10440 | −8140 | 1823 | 4421 | 2909 | |
|
||||||||||||||||||||
| from Kelvin | to Kelvin | |
|---|---|---|
| Celsius | [°C] = [K] − 273.15 | [K] = [°C] + 273.15 |
| Fahrenheit | [°F] = [K] × 9⁄5 − 459.67 | [K] = ([°F] + 459.67) × 5⁄9 |
| Rankine | [°R] = [K] × 9⁄5 | [K] = [°R] × 5⁄9 |
| For temperature intervals rather than specific temperatures, 1 K = 1 °C = 9⁄5 °F = 9⁄5 °R |
||
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units (SI) and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F).[1]
The Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist 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 or typeset as a degree. The kelvin is the primary unit of measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude. Subtracting 273.16 K from the temperature of the triple point of water (0.01 °C) makes absolute zero (0 K) equivalent to −273.15 °C (−460 °F).
Contents
|
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.
Before 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 unit 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 (although for some reason, the Rankine scale continued to use "degree Rankine"), 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 International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (K). However, when an SI unit is spelled out in English, it should always begin with a lower case letter (kelvin), except in a situation where any word in that position 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. When spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm (e.g., "the triple point of water is exactly 273.16 kelvins" [8]).
The SI unit symbol for the kelvin 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 quantities 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").[9][10]
Unicode provides a compatibility character for the kelvin at U+212A (decimal 8490), for compatibility with CJK encodings that provide such a character (as such, in most fonts the width is the same as for fullwidth characters).
In science and in engineering, degrees Celsius and kelvins are often used simultaneously in the same article (e.g., "...its measured value was 0.01028 °C with an uncertainty of 60 µK..."). This practice is permissible because the degree Celsius is a special name for the kelvin for use in expressing Celsius temperatures and the magnitude of the degree Celsius is exactly equal to that of the kelvin.[11] Notwithstanding that the official endorsement provided by Resolution 3 of the 13th CGPM states, "a temperature interval may also be expressed in degrees Celsius", the practice of simultaneously using both "°C" and "K" remains widespread throughout the scientific world as the use of SI prefixed forms of the degree Celsius (such as "µ°C" or "microdegrees Celsius") to express a temperature interval has not been widely adopted.[4]
In 2005 the CIPM embarked on a program to redefine, amongst others, the kelvin using a more rigorous basis than was in use. The current (2010) definition is unsatisfactory for temperatures below 20 K and above 1300 K.[12] It is anticipated that the program will be completed in time for its adoption by the CGPM at its 2011 meeting. The committee proposes defining the kelvin as the temperature scale for which Boltzmann's constant is 1.3806505×10−23 J/K exactly.[13]
From a scientific point of view, this will link temperature to the rest of SI and result in a stable definition that is independent of any particular substance. From a practical point of view, the redefinition will pass unnoticed; water will still freeze at 0 °C (32 °F, 273.15 K).[14]
The kelvin is often used in the measure of the colour temperature of light sources. Colour temperature is based upon the principle that a black body radiator emits light whose colour depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish. Colour temperature is important in the fields of image projection and photography where a colour temperature of approximately 5600 K is required to match "daylight" film emulsions. In astronomy, the stellar classification of stars and their place on the Hertzsprung–Russell diagram are based, in part, upon their surface temperature, known as effective temperature. The photosphere of the Sun, for instance, has an effective temperature of 5778 K.
In electronics, the kelvin is used as an indicator of how noisy a circuit is in relation to an ultimate noise floor, i.e. the noise temperature. The so-called Johnson–Nyquist noise of discrete resistors and capacitors is a type of thermal noise derived from the Boltzmann constant and can be used to determine the noise temperature of a circuit using the Friis formulas for noise.
| Look up kelvin in Wiktionary, the free dictionary. |
|
||||||||
|
||||||||||||||||||||
全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.
| リンク元 | 「ケルビン」 |
| 関連記事 | 「kelvin」 |