11/09/2012PHY 113 A Fall Lecture 281 PHY 113 A General Physics I 9-9:50 AM MWF Olin 101 Plan for Lecture 28: Chapter 19: The notion of temperature 1.Comments on Exam 3 2.Temperature equilibrium 3.Temperature scales 4.Temperature in ideal gases

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11/09/2012PHY 113 A Fall Lecture 283 Dictionary definition: temperature – a measure of the the warmth or coldness of an object or substance with reference to some standard value. The temperature of two systems is the same when the systems are in thermal equilibrium. “Zeroth” law of thermodynamics: If objects A and B are separately in thermal equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other. T 1 T2T2 T3T3 Not equilibrium: Equilibrium:

11/09/2012PHY 113 A Fall Lecture 284 Constant temperature “bath” T T At equilibrium:

11/09/2012PHY 113 A Fall Lecture 285 Temperature scales T F =9/5 T C + 32 Kelvin scale: T = T C o T 

11/09/2012PHY 113 A Fall Lecture 286 iclicker question: Suppose you find yourself in a hotel in Europe or Canada. Which Celsius temperature would you set the thermostat for comfort? A.-20 o C B.+20 o C C.+40 o C D.+60 o C E.+80 o C

11/09/2012PHY 113 A Fall Lecture 287 There is a lowest temperature: T 0 = o C = 0 K Kelvin (“absolute temperature”) scale T C = T K Example – Room temperature = 68 o F = 20 o C = K

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11/09/2012PHY 113 A Fall Lecture 289 Effects of temperature on matter Solids and liquids L i (equilibrium bond length at T i ) Model of a solid composed of atoms and bonds LL Thermal exansion:  L =  L i  T

11/09/2012PHY 113 A Fall Lecture 2810 Typical expansion coefficients at T C = 20 o C: Linear expansion:  L =  L i  T Steel:  = 11 x / o C Concrete:  = 12 x / o C Volume expansion: V=L 3   V = 3  V i  T =  V i  T Alcohol:  = 1.12 x / o C Air:  = 3.41 x / o C

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11/09/2012PHY 113 A Fall Lecture 2812 Brass Steel

11/09/2012PHY 113 A Fall Lecture 2813 Switch in thermostat Modern thermostats use electrical circuits to detect temperature

11/09/2012PHY 113 A Fall Lecture 2814 Effects of temperature on materials – continued strange case of water:

11/09/2012PHY 113 A Fall Lecture 2815 Effects of temperature on materials – continued -- ideal gas “law” (thanks to Robert Boyle ( ), Jacques Charles ( ), and Gay- Lussac ( ) pressure in Pascals volume in m 3 # of moles temperature in K J/(mol K) 1 mole corresponds to x molecules

11/09/2012PHY 113 A Fall Lecture 2816 P 0 =12.6 atm T 0 =27.5 o C n 0 P=? T=81.0 o C n=n 0 /3

11/09/2012PHY 113 A Fall Lecture 2817 Comments about Exam 3 iclicker question: Possible review of Exam 3 material A.I would like to attend a review class session to go over the exam B.I would like to meet individually or in a small group to go over the exam C.I would like to forget the exam and take my chances that it is possible to live a full life without knowing about rotations, equilibrium, simple harmonic motion, and gravity

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