ThermodynamicsPhysics 207, Lecture 25, Nov. 29TemperatureHeatZeroth Law of ThermodynamicsWhat to do with heat and how do we assess it?Temperature scalesModern Definition of Kelvin ScaleSome interesting factsThermometers: Devices to measure temperatureThermal expansionSHM and quadratic potentialsLecture 25, Exercise 1 Thermal expansionLecture 25, Example 2 Thermal expansionLecture 25, Example 3 Thermal expansionLecture 25, Exercise 4 Thermal ExpansionSlide 17Slide 18Thermal Expansion and TeethSlide 20Slide 21Applications of Thermal Expansion – Bimetallic StripSpecial system: WaterLecture 25, Exercise 5Ideal gas: Macroscopic descriptionBoltzmann’s constantThe Ideal Gas LawExampleLecture 25, RecapPhysics 207: Lecture 25, Pg 1ThermodynamicsThermodynamicsA practical science initially concerned with economics, industry, real life problems. DYNAMICS -- Concerned with the concepts of energy transfers between a system and its environment and the resulting temperature variationsConcerns itself with the physical and chemical transformations of matter in all of its forms: solid, liquid, and gasConcerns the processes that “violate” conservation of mechanical energy -- friction -- via the conversion between thermal and mechanical energy.Physics 207: Lecture 25, Pg 2Physics 207, Physics 207, Lecture 25, Nov. 29Lecture 25, Nov. 29 Agenda: Chapter 19, TemperatureAgenda: Chapter 19, Temperature Heat Thermal Expansion Temperature and Zeroth Law of Thermodynamics Temperature scales Kinetic Theory of Gases (Ch. 22)Kinetic Theory of Gases (Ch. 22)Question: What has more internal energy, a 10 kg bar Question: What has more internal energy, a 10 kg bar of glowing red hot iron (at ~800 C) or a 100 kg person of glowing red hot iron (at ~800 C) or a 100 kg person (at 37 C)? Which can effect a larger heat transfer?(at 37 C)? Which can effect a larger heat transfer?Assignments:Assignments:Problem Set 9 due Tuesday, Dec. 5, 11:59 PMProblem Set 9 due Tuesday, Dec. 5, 11:59 PMMonday, Chapter 20 (Heat & the First Law of Thermodynamics)Monday, Chapter 20 (Heat & the First Law of Thermodynamics)Physics 207: Lecture 25, Pg 3TemperatureTemperatureTemperature: A standardized measure of the motion of the individual atoms and molecules in a gas, liquid, or solid. related to average kinetic energy of constituentsHigh temperature: The constituents are moving around energetically In a gas at high temperature the individual gas molecules are moving about independently at high speeds. In a solid at high temperature the individual atoms of the solid are vibrating energetically in place.The converse is true for a "cold" object. In a gas at low temperature the individual gas molecules are moving about sluggishly. There is an absolute zero temperature at which the classical motions of atoms and molecules practically stop. Quantum zero point energy cannot be removed (Planck’s constant is not zero.)Physics 207: Lecture 25, Pg 4HeatHeatSolids, liquids or gases have internal energy Kinetic energy from random motion of molecules translation, rotation, vibration At equilibrium, it is related to temperatureHeat: Transfer of energy from one object to another as a result of their different temperaturesThermal contact: energy can flow between objectsT1T2U1U2>Physics 207: Lecture 25, Pg 5Zeroth Law of ThermodynamicsZeroth Law of ThermodynamicsThermal equilibrium is established when objects in thermal contact cease heat transfer They are said to be at the same temperatureT1T2U1U2=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.ACBPhysics 207: Lecture 25, Pg 6What to do with heat and how do we assess it?What to do with heat and how do we assess it?Conversion of energy from one form to another often involves heat. Example: A power plant burns coal (chemical energy) and “heat” is used to produces steam (boiling water at high pressure) which turns a steam turbine generator. This provides point electricity which must be transferred to its use location. There is also waste heat. In a best case scenario only about 35-40% of the original chemical energy is utilized.Temperature allows to discern the direction of energy transferPhysics 207: Lecture 25, Pg 7Temperature scalesTemperature scalesThree main scales212Farenheit100Celcius32 0 273.15373.15KelvinWater boilsWater freezes0-273.15-459.67Absolute ZeroTF95TC 32oFTC59TF 32oF TCT 273.15KT TC 273.15 KPhysics 207: Lecture 25, Pg 8Modern Definition of Kelvin ScaleModern Definition of Kelvin ScaleThe temperature of the triple point on the Kelvin scale is 273.16 KTherefore, the current definition of the Kelvin is defined as 1/273.16 of the temperature of the triple point of waterThe triple point of water occurs at 0.01o C and 4.58 mm (0.06 atm)of HgPhysics 207: Lecture 25, Pg 9Some interesting factsSome interesting factsIn 1724, Gabriel Fahrenheit made thermometers using mercury. The zero point of his scale is attained by mixing equal parts of water, ice, and salt. A second point was obtained when pure water froze (originally set at 30oF), and a third (set at 96°F) “when placing the thermometer in the mouth of a healthy man”. On that scale, water boiled at 212. Later, Fahrenheit moved the freezing point of water to 32 (so that the scale had 180 increments).In 1745, Carolus Linnaeus of Upsula, Sweden, described a scale in which the freezing point of water was zero, and the boiling point 100, making it a centigrade (one hundred steps) scale. Anders Celsius (1701-1744) used the reverse scale in which 100 represented the freezing point and zero the boiling point of water, still, of course, with 100 degrees between the two defining points.T (K)1081071061051041031001010.1Hydrogen bombSun’s interiorSolar coronaSun’s surfaceCopper meltsWater freezesLiquid nitrogenLiquid hydrogenLiquid heliumLowest T~ 10-9KPhysics 207: Lecture 25, Pg 10Thermometers: Devices to measure temperatureThermometers: Devices to measure temperatureMake use of physical properties that change with temperatureMany physical properties can be usedvolume of a liquidlength of a solidpressure of a gas held at constant volumevolume of a gas held at constant pressureelectric resistance of a conductorcolor of a very hot
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