Physics 121 April 10 2008 Temperature Heat Frank L H Wolfs Department of Physics and Astronomy University of Rochester Physics 121 April 10 2008 Course Information Topics to be discussed today Temperature Frank L H Wolfs Department of Physics and Astronomy University of Rochester Physics 121 April 10 2008 Homework set 8 is due on Saturday morning April 12 at 8 30 am Homework set 9 is now available and will be due on Saturday morning April 19 at 8 30 am This assignment only contains WeBWorK problems Requests for regarding part of Exam 1 and 2 need to be given to me by April 17 You need to write down what I should look at and give me your written request and your blue exam booklet s Frank L H Wolfs Department of Physics and Astronomy University of Rochester Physics 121 April 10 2008 At this point we have finished our discussion of the material that will be covered on Exam 3 Chapters 10 11 12 and 14 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 find your 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 to what the Physics 121 staff can do we can not meet 4 hours a week with each of you individually Frank L H Wolfs Department of Physics and Astronomy University of Rochester Physics 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 Rochester Thermodynamics The materials we encounter in our daily life can be considered to be made up out of atoms In principle we can describe the macroscopic properties of these materials such as temperature and volume in terms of the microscopic properties of the individual atoms such as velocity and inter atomic forces In practice this is very difficult Thermodynamics is the field of physics that studies the description of the state of matter in terms of its macroscopic properties Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Temperature An important thermodynamic variable is temperature Properties of many bodies change as their thermal environment is altered For example thermal expansion contraction pressure changes etc We can use these changes in properties to develop a tool that allows us to measure temperature the thermometer Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Measuring temperature In order to measure the temperature of a system we need to bring the thermometer in contact with the system We must wait long enough to ensure that the thermometer and the system are in thermal equilibrium have the same temperature This approach relies on the zeroth law of thermodynamics Temperature is a property of a body and two bodies are in thermal equilibrium if their temperatures are equal If the thermometer initially has a different temperature than the system energy will flow to provide thermal equilibrium and the temperature of both systems will change Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Measuring temperature In order to measure temperature we must Agree on a standard reference point to which we assign a certain temperature Agree on a unit Agree on a standard thermometer against which all other thermometers can be calibrated The unit of temperature will be the Kelvin K The standard reference point is the triple point of water T 273 16 K http www fluke fr common prod pages pages hart products tpw htm Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Measuring temperature The standard thermometer is the constant volume gas thermometer The bulb of the thermometer which is filled with gas is put in thermal contact with the system to be studied If nothing else would change the change in pressure would change the mercury level The reservoir on the right is now adjusted to change the mercury level so that the gas volume remains unchanged Frank L H Wolfs Reservoir h T Department of Physics and Astronomy University of Rochester Thermodynamic variables Measuring temperature Fixed The difference in height between the levels h is measured The difference in height can be used to determine the pressure of the gas Reservoir h p p0 gh T where p0 is the atmospheric pressure and is the density of the mercury The temperature of the body is defined in terms of the pressure p T Cp Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Measuring temperature The definition of the temperature of the body in terms of the pressure p T Cp requires us to determine one parameter C The device can thus be fully calibrated by bringing it in contact with a triple point of water cell Fixed Reservoir h T T3 273 16 K Cp3 or C 273 16 p3 Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Measuring temperature In general we can thus find the temperature of the body by comparing the measured pressure with the triple point pressure T T3 p p3 273 16 p p3 The method described here depends slightly on the amount and the type of gas in the bulb However this dependence is reduced when we use smaller and smaller amounts of gas Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Temperature scales The Kelvin is not frequently used in our daily life More common temperature scales are the Celsius scale 0 is defined as the freezing point of water 100 is defined as the boiling point of water and the Fahrenheit scale 32 is defined as the freezing point of water 212 is defined as the boiling point of water Frank L H Wolfs Department of Physics and Astronomy University of Rochester Thermodynamic variables Thermometers Thermometers exist in many different forms The design of a thermometer depends on how they are going to be used and the range of temperatures to be measured All thermometers rely on using macroscopic