lsli07.4up

lsli07.4up - 07-1 07-1 07-2 07-2 Temperature Denition: The...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
07-1 07-1 Temperature 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 13:25, 23 December 1997 from lsli07. 07-1 07-2 07-2 Kelvin’s Thermodynamic Temperature Scale 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, T tr ,isused . T tr is temperature at which water can simultaneously be in the solid, liquid, and gas states: 0 . 01 C. Confine an ideal gas in a container of fixed volume, S . Bring the gas to temperature T tr . Call the pressure of this gas P tr . By definition (of the Kelvin scale) this temperature is T tr , 273 . 16 K. The ideal gas law: PS = n < T . Substituting, P tr S = n < 273 . 16 K. Then n < = P tr S 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 = n < . Substituting for n < using the quantity obtained above yields T = 273 . 16 K P tr S = 273 . 16 K P P tr . 07-2 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 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 Cat800 C. 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 13:25, 23 December 1997 from lsli07. 07-3 07-4 07-4 For ITS-90: ( . 65 K , 5 . 0K) Vapor-pressure relation between two isotopes of helium. (3 . 0K , 24 . 5561 K) Helium fixed-volume thermometer. (Like thermometer used in thermodynamic scale, except helium replaces the ideal gas.) (13 . 8033 K , 1234 . 93 K) Resistance of platinum. > 1234 . 93 K: Based on radiated light. 07-4 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 from lsli07.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/28/2011 for the course EE 4770 taught by Professor Staff during the Fall '99 term at LSU.

Page1 / 10

lsli07.4up - 07-1 07-1 07-2 07-2 Temperature Denition: The...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online