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# ee 4 - EE 4770 Lecture Notes Generated from file lsli07.dvi...

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EE 4770 Lecture Notes Generated from file lsli07.dvi. This page was generated using an imperfect translator. Text may be poorly positioned and mathematics will be barely readable. Illustrations will not show at all. If possible, view the PostScript or PDF versions of these notes. 07-1 Temperature 07* *-1 Definition: The translational (e.g., wiggling around) energy : : : : : :of particles in a system. No practical way to measure : : : : : :velocity of every particle : : : : : :in most systems of interest. Instead, temperature scales are defined. There are two types: - The thermodynamic temperature scale. "Really" measures temperature. - Practical temperature scales. Approximations of thermodynamic scale. Much easier to measure temperature on a practical scale. For temperatures of interest, differences are very small. 07-1 EE 4770 Lecture Transparency. Formatted 8:22, 27 January 1999 from lsli07. * * 07-1 07-2 07* *-2 Kelvin's Thermodynamic_________ Temperature Scale

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Due to William Thomson, a.k.a., Lord Kelvin (1824-1907). Start with a precise temperature that can easily be reproduced. The triple point of water, Ttr, is used. Ttr is temperature at which : : : : : :water can simultaneously be in : : : : : :the solid, liquid, and gas states: 0:01 ffiC. - Confine an ideal gas in a container of fixed volume, S. - Bring the gas to temperature Ttr. Call the pressure of this gas Ptr. By_definition___ (of the Kelvin scale) this temperature is Ttr , 273:16 K. The ideal gas law: P S = n< = ___PtrS____273:16.K - Bring the same system to another temperature, T . Call the pressure at this temperature, P . Solving for T in the gas law: T = P_S_n<. Substituting for n< using the quantity obtained above yields T = P S 273:16_K___P= 273:16 K P___: trS Ptr 07-2 EE 4770 Lecture Transparency. Formatted 8:22, 27 January 1999 from lsli07. * * 07-2 07-3 07* *-3 Practical Temperature Scales_ Designed to be easy (relatively) to measure.
Scales are revised every few decades. Latest revision in 1990, called ITS-90. (International Temperature Scale.) Older scale (1968), IPTS-68. (International Practical Temperature Scale) Difference between ITS-90 and IPTS-68 : : : : : :is as large as 0:4 ffiCat 800 ffiC. At human-tolerable temperatures, : : : : : :difference is in hundreths of a degree. All practical scales are identical at the triple point of water. How a practical temperature scale is defined: A set of fixed points is established, : : : : : :for example the triple point of water. A temperature is assigned to each fixed point, : : : : : :based on the thermodynamic scale. Accurate thermometers (transducers) are chosen. Functions are defined mapping : : : : : :the thermometers' output to temperature : : : : : :so that they pass through the fixed points. ) Temperatures defined in terms of fixed points and special transducers. 07-3 EE 4770 Lecture Transparency. Formatted 8:22, 27 January 1999 from lsli07. * * 07-3 07-4 07* *-4 For ITS-90: - (:65 K; 5:0 K) Vapor-pressure relation between two isotopes of helium.

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- (3:0 K; 24:5561 K) Helium fixed-volume thermometer.
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