The Kelvin scale is an absolute thermodynamic temperature scale that uses its absolute zero absolute zero, the temperature at which all thermal motions cease in the classical description of thermodynamics. The kelvin (symbol: K) is the basic unit of temperature in the International Unit System (SI). Kelvin is defined as the fraction 1 / 273.16 from the thermodynamic temperature of the water triple point (precisely 0.01 Â ° C or 32.018 Ã, Â ° F). In other words, it is defined in such a way that the water triple point is exactly 273.16Ã, K.
The Kelvin scale is named after the Belfast-born engineer and physicist William Thomson, 1st Baron Kelvin (1824-1907), who wrote of the need for an "absolute thermometry scale". Unlike the degrees Fahrenheit and degrees Celcius, kelvin is not called or written as a degree. Kelvin is the main unit of temperature measurement in physics, but is often used in conjunction with degrees Celsius, which has the same magnitude. This definition implies that absolute zero (0 K) is equivalent to -273.15 Â ° C (-459.67 Â ° F).
To state the temperature difference or interval, using kelvin instead of degrees Celsius helps to avoid situations when people mistakenly calculate the amount for Celsius temperature. Kelvin is the right temperature unit for use in derivative units, such as W/(mÃ, Â · K) or has a prefix, such as milli in mK.
Video Kelvin
Histori
In 1848, William Thomson, later made Lord Kelvin, wrote in his paper, On the Absolute Thermometric Scale, the need for a scale in which "infinite cold" (absolute zero) is the zero point scale, and which using degrees Celsius to increase its unit. Kelvin calculated that absolute zero was equivalent to -273 ° C at the air thermometer at the time. This absolute scale is known today as Kelvin's thermodynamic temperature scale. The Kelvin value of "-273" is the negative inverse 0.00366 - the coefficient of gas expansion received per degree Celsius relative to the point of ice, providing exceptional consistency to the currently accepted value.
In 1954, Resolution 3 of the 10th General Conference on Weight and Size (CGPM) gave Kelvin his modern definition by pointing to the point of triple water as the second defining point and setting the temperature to exactly 273.16 kelvins.
In 1967/1968 Resolution 3 of the 13th CGPM renamed the thermodynamic thermodynamics rise unit, the K symbol, replaced the "degrees Kelvin", the Ã, Â ° K symbol. Furthermore, it was useful to more explicitly define the magnitude of the increase unit, the 13th CGPM is also held in Resolution 4 that "Kelvin, the thermodynamic temperature unit, is equal to the 1 / 273.16 fraction of the thermodynamic temperature point triple water. "
In 2005 The ComitÃÆ'Â © International des Poids et Mesures (CIPM), a CGPM committee, asserted that for the purpose of triple water point temperature depiction, the Kelvin thermodynamic scale temperature scale definition would refer to water having an isotope composition determined as VSMOW.
Maps Kelvin
Use convention
When spelled or spoken, the unit is mapped using the same grammar rules as for other SI units such as volts or ohms (eg "The precise water triple point is 273.16 kelvin.) When reference is made to" Kelvin scale ", the word" kelvin "- usually a noun - functions by adjectives to modify" scale "nouns and capitalized.like most other SI unit symbols (angular symbols, eg 45 Â ° 3? 4?, are exceptions) exist the space between the numeric value and the kelvin symbol (eg "99.987 K").
Prior to the 13th CGPM in 1967-1968, kelvin units were called "degrees", similar to other temperature scales at the time. It is distinguished from other scales by the adjective adjective "Kelvin" ("degrees Kelvin") or by "absolute" (the "absolute title") and the symbol is Ã, Â ° K. The last term (absolute degree), which is the unit's official name from 1948 to 1954, is ambiguous because it can also be interpreted as referring to the Rankine scale. Prior to the 13th CGPM, the plural was "absolute degree". The 13th CGPM changed the name of the unit to "kelvin" (symbol: K). The "degree" neglect indicates that it is not relative to arbitrary reference points such as the Celsius and Fahrenheit scales (although the Rankine scale continues to use "Rankine degrees"), but an absolute size unit that can be algebraically manipulated (eg multiplied by two to show two times the amount of "average energy" available among the basic levels of system freedom).
Use concurrent with degrees Celsius
In science and engineering, degrees Celsius and kelvin are often used simultaneously in the same article, where absolute temperature is given in degrees Celsius, but temperature intervals are given in kelvin. For example. "The measured value is 0.010 28 Ã, Â ° C with uncertainty 60 Ã,ÂμK."
This practice is permissible because Celcius degree is a special name for kelvin to be used in expressing relative temperatures, and the degree of Celsius is exactly the same as that of kelvin. Although the official support provided by Resolution 3 of the 13th CGPM states "the temperature interval can also be expressed in degrees Celsius", the practice of simultaneously using " ° C" and "K" is widespread throughout the scientific world. The use of SI begins with forms of degrees Celsius (such as "Ã,μÃ,  ° C" or "microdegree Celsius") to express the temperature interval has not been widely adopted.
Proposed redefinition
In 2005 CIPM started a program to redefine kelvin (along with other SI units) using a more rigorous experimental methodology. The current definition in 2016 is not satisfactory for temperatures below 20 K and above 1300Ã, K . In particular, the committee proposes redefining the kelvin in such a way that Boltzmann constantly takes the exact value 1,380 6505 ÃÆ' - 10 -23 J/K . The Committee hopes that the program will be completed on time for adoption by CGPM at its 2011 meeting, but at the 2011 meeting the decision was postponed to a 2014 meeting when it will be considered part of a larger program.
Redefinition was further delayed in 2014, awaiting more accurate measurements of the Boltzmann constant in the current definition, but is expected to be adopted at the 26th CGPM by the end of 2018.
From a scientific point of view, this will connect the temperature to the rest of the SI and produce a stable definition that does not depend on a particular substance. From a practical point of view, redefinition will pass unnoticed; water will still freeze at 273.15 K (0 Â ° C).
Practical use
Color temperature
Kelvin is often used in light source color temperature. The color temperature is based on the principle that the radiator of the black body emits a light whose color depends on the temperature of the radiator. Black body with temperature below about 4000Ã, K looks red, while above about 7500Ã, K looks bluish. The color temperature is important in the area of ​​image projection and photography, where the color temperature around 5600Ã, K is required to match the "daylight" film emulsion. In astronomy, the classification of stellar stars and their place on the Hertzsprung-Russell diagram is based, in part, on their surface temperature, known as the effective temperature. The photosphere of the Sun, for example, has an effective temperature of 5778Ã, K .
Digital cameras and photography software often use the color temperature in K in the edit menu and settings. The simple guide is the higher the color temperature, the more white or blue the image is. Reduced color temperature will produce images that are more dominated by reddish "warm" colors.
Kelvin as a noise measure
In electronics, kelvin is used as an indicator of how noisy a circuit is in relation to an ultimate noise floor, ie the noise temperature. The so-called Johnson-Nyquist noise resistors and discrete capacitors are a type of thermal noise derived from the Boltzmann constant and can be used to determine the disturbance temperature of the circuit using the Friis formula for noise.
Unicode characters
The symbol is encoded in Unicode on codepoint U 212A K kelvin sign . However, this is the compatibility character provided for compatibility with the old coding. The Unicode standard recommends the use of U 004B K Latin capital letters k instead; that is, the normal capital K. "Three letter-shaped symbols have been given canonical equations to ordinary letters: U 2126 ? ohm mark , U 212A K kelvin sign , and U 212B ÃÆ'â € | angstrom sign In the three examples, regular mail should be used. "
See also
Notes and references
External links
Source of the article : Wikipedia
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