Date: 04/16/2002 at 22:31:02 From: Milan Subject: Degrees Kelvin Why is it considered to be wrong when you write, for example, 0 degrees Kelvin? I have been told by my math teacher to write 0 Kelvin instead, without the degrees. I find this quite awkward as I am used to writing the 'degrees'. I was wondering if you could explain to me why. Thank you.
Date: 04/17/2002 at 09:06:28 From: Doctor Peterson Subject: Re: Degrees Kelvin Hi, Milan. I can't say I understand why either, but this is the decree of the International Bureau of Weights and Measures, the organization that defines the SI metric system: How Many? A Dictionary of Units of Measurement - Russ Rowlett http://www.unc.edu/~rowlett/units/dictD.html degree Kelvin an obsolete name for the kelvin. In the International System, temperatures on the absolute temperature scale are stated in kelvins, not in degrees Kelvin. For more detail, see: NIST Reference on Constants, Units, and Uncertainty http://physics.nist.gov/cuu/Units/kelvin.html The definition of the unit of thermodynamic temperature was given in substance by the 10th CGPM (1954) which selected the triple point of water as the fundamental fixed point and assigned to it the temperature 273.16 K, so defining the unit. The 13th CGPM (1967) adopted the name kelvin (symbol K) instead of "degree Kelvin" (symbol °K) and defined the unit of thermodynamic temperature as follows: The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. ... The unit of Celsius temperature is the degree Celsius, symbol °C, which is by definition equal in magnitude to the kelvin. A difference or interval of temperature may be expressed in kelvins or in degrees Celsius (13th CGPM, 1967). I have never found an actual explanation of the reason for this change. My guess is that they want it to look like any other SI unit. The various kinds of degrees are labeled as "degrees" (the unit itself) followed by "Celsius" or whatever (identifying the system whose degree and 0 point are being used). Since the kelvin is the standard in SI, I suppose they feel there should be no need for such a two-level name, which suggests that there might actually be rivals to the SI! - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/
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