William Thomson

Thermodynamic and Celsius temperatures in degrees

The Kelvin (unit symbol: K) is the SI base unit of the thermodynamic temperature and at the same time the legal temperature unit; it is also used to indicate temperature differences. In addition, in Germany and Austria the degree Celsius (unit sign : ° C) is the legal unit for the specification of Celsius temperatures and their differences.

Thermodynamic temperatures and Celsius temperatures have the same scaling, so the units Kelvin and degrees Celsius are the same; While the zero point of the Kelvin scale is the absolute zero point , the zero point of the scale is shifted from Celsius temperatures to the freezing point temperature of water under normal conditions (273.15 K). Hence 0 K = −273.15 ° C; 273.15 K = 0 ° C. 274.15 K is 1 ° C etc. A temperature difference of, for example, 10 K is equal to a difference of 10 ° C. The obsolete indication of temperature difference degrees (grd) has been replaced by the Kelvin.Until 1967 the unit name was degrees Kelvin , the unit symbol was ° K. The Kelvin was named after William Thomson, later Lord Kelvin, who introduced the thermodynamic temperature scale at the age of 24.


Definition Kelvin degree

The Kelvin was defined by the CGPM for the first time in 1954 – at that time as the Kelvin degree – and in its current form again in 1968 and defined as the SI base unit: “The Kelvin, the unit of thermodynamic temperature , is the 273.16th part of the thermodynamic temperature of the triple point of water.” (Official translation from English) What is meant is pure water, the isotope composition of which should be based on VSMOW.

The zero point of the Kelvin scale is located at the absolute zero at -273.15  ° C .
However, this temperature cannot be measured and reached according to Nernst’s theorem since particles at 0 K would have no kinetic energy (the remaining energy – zero point energy – is a result of the Heisenberg uncertainty principle ). A temperature difference of one Kelvin is the 273.16th part of the temperature difference between the absolute zero point and the thermodynamic temperature of the triple point of water (0.01 ° C).

William Thomson

Differences between Kelvin scale and Celsius temperatures

The difference to degree symbol Celsius is that the temperatures of the freezing and boiling points of the water at normal pressure (ie an air pressure of 1013.25 hPa ) are used as fixed points on the Celsius temperature scale. The absolute zero point (−273.15 ° C) is used as the 0 K on the Kelvin scale. In contrast, temperature values ​​with negative numbers can also appear in the Celsius temperature scale. Visit to copy degree symbol easily https://degreessymbolsign.com/

Story about degree William Thomson

The divisions of the absolute temperature scale proposed by William Thomson were initially called ° A (for absolute). In the SI was from 1948 to 1968, the ° C (degrees Kelvin to 1954 as “absolute level”) as the temperature unit. In addition, temperature differences – deviating from temperature information – were given in deg (degrees) during the period mentioned. The use of these old units is no longer permitted in Germany today. As early as 1948, the CGPM set an absolute thermodynamic scale with the triple point of water as the only fundamental fixed point, but not yet linked to the temperature.

The steadily reduced uncertainties in the measurement of the temperature of the water triple point made it possible in the 21st century to determine the influence of the isotope composition on the triple point of the water (order of magnitude of approximately 0.1 mK). The necessary definition of the Kelvin definition was made in 2005 at the 94th meeting of the CIPM, according to which purified standard ocean water should be used as a reference point; however, the wording of the Kelvin degrees symbol definition has not been changed.

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