Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121, April 10, 2008.Temperature/Heat.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.April 10, 2008.• Course Information• Topics to be discussed today:• TemperatureFrank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.April 10, 2008.• Homework set # 8 is due on Saturday morning, April 12, at8.30 am.• Homework set # 9 is now available and will be due onSaturday morning, April 19, at 8.30 am. This assignmentonly contains WeBWorK problems.• Requests for regarding part of Exam # 1 and # 2 need to begiven to me by April 17. You need to write down what Ishould look at and give me your written request and yourblue exam booklet(s).Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.April 10, 2008.• At this point we have finished our discussion of the materialthat will be covered on Exam # 3 (Chapters 10, 11, 12, and14).• A few suggestions on how to prepare for the exam:• Look at the results of exams 1 and 2 and see where you went wrong.• Review the solutions to the homework assignments. Did you findyour solution using the easiest approach?• Complete the practice exam (without using the book as a reference)as a way to judge how well prepared you are for the exam.• Use the study guide (quizzes, worked out problems, etc.).• Practice problem recognition using the end-of-the-chapter problems.• Seek help when you need help, but realize that there are limits towhat the Physics 121 staff can do (we can not meet 4 hours a weekwith each of you individually).Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.April 10, 2008.• Material included on Exam # 3:• Chapter 10: all Sections except Section 10-10.• Chapter 11: all Sections except Sections 11-8 and 11-9.• Chapter 12: all Sections except Section 12-6.• Chapter 14: all Sections.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamics.• The materials we encounter in our dailylife can be considered to be made up outof atoms.• In principle we can describe themacroscopic properties of these materials(such as temperature and volume) interms of the microscopic properties ofthe individual atoms (such as velocityand inter-atomic forces).• In practice this is very difficult.• Thermodynamics is the field of physicsthat studies the description of the state ofmatter in terms of its macroscopicproperties.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Temperature.• An important thermodynamicvariable is temperature.• Properties of many bodies changeas their thermal environment isaltered. For example, thermalexpansion/contraction, pressurechanges, etc.• We can use these changes inproperties to develop a tool thatallows us to measuretemperature: the thermometer.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Measuring temperature.• In order to measure the temperature of a system, we need tobring the thermometer in contact with the system.• We must wait long enough to ensure that the thermometerand the system are in thermal equilibrium (have the sametemperature).• This approach relies on the zeroth law of thermodynamics:Temperature is a property of a body, and two bodies are in thermalequilibrium if their temperatures are equal.• If the thermometer initially has a different temperature thanthe system, energy will flow to provide thermal equilibriumand the temperature of both systems will change!Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Measuring temperature.• In order to measure temperaturewe must:• Agree on a standard referencepoint to which we assign a certaintemperature.• Agree on a unit.• Agree on a standard thermometeragainst which all otherthermometers can be calibrated.• The unit of temperature will bethe Kelvin (K).• The standard reference point isthe triple point of water (T =273.16 K).http://www.fluke.fr/common/prod_pages/pages/hart/products/tpw.htmFrank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Measuring temperature.• The standard thermometer is theconstant volume gasthermometer.• The bulb of the thermometer,which is filled with gas, is put inthermal contact with the systemto be studied.• If nothing else would change, thechange in pressure would changethe mercury level.• The reservoir on the right is nowadjusted to change the mercurylevel so that the gas volumeremains unchanged.hTReservoirFrank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Measuring temperature.• The difference in height between thelevels (h) is measured.• The difference in height can be usedto determine the pressure of the gas:p = p0 + ρghwhere p0 is the atmosphericpressure and ρ is the density of themercury.• The temperature of the body isdefined in terms of the pressure p:T = CphTReservoirFixedFrank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Measuring temperature.• The definition of the temperature ofthe body in terms of the pressure p(T = Cp) requires us to determineone parameter (C).• The device can thus be fullycalibrated by bringing it in contactwith a triple-point of water cell:T3 = 273.16 K = Cp3orC = 273.16/p3hTReservoirFixedFrank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Measuring temperature.• In general we can thus find thetemperature of the body bycomparing the measured pressurewith the triple-point pressure:T = T3 (p/p3) = 273.16 (p/p3)• The method described heredepends slightly on the amountand the type of gas in the bulb.However, this dependence isreduced when we use smaller andsmaller amounts of gas.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterThermodynamic variables.Temperature scales.• The Kelvin is not frequently usedin our