《大学物理》英文课件18 Temperature, Heat, and The First Law of Thermodynamics(示)

1、? ?大学物理大学物理? ?英文课件英文课件18 18 Temperature, Heat, Temperature, Heat, and The First Law of and The First Law of Thermodynamics(Thermodynamics(示示) )Favr , , ,Mechanics Newtons 3 Laws Thermodynamics: The study of internal energy (thermal energy) Thermodynamic LawsKey concept: Temperature TThermodynamicsKe

2、lvin scale;Has lower limit = absolute zero = 10-; no upper limitTemperatureProperties change with temperatureThermoscope ThermometerThe Zeroth Law of Thermodynamics The Zeroth Law of Thermodynamics: If bodies A and B are each in thermal equilibrium with a third body T, then A and B are in thermal eq

3、uilibrium with each other. Every body has a property called temperature. When two bodies are in thermal equilibrium, their temperatures are equal. A useful definition of temperature.Measuring Temperature 1. Set up a temperature scale 2. Standard fixed-point temperature sizeKelvin scale Triple point

4、of water T3= 273.16 Kelvin (K) for liquid water, solid ice, and water vapor1/ 273.16 K = the size of the Kelvin of the difference between the triple-point temperature of water and absolute zero.IceTriple point cellConstant-Volume Gas ThermometerCpT 33CpT 333K)16.273(ppppTT30gaslimK)16.273(ppTMeasuri

5、ng Temperature Calibrate a metal rod to a thermometerMedical thermometerThe Celsius and Fahrenheit ScalesCelsius scale triple point 0.01 oCSame size as Kelvino15.273 TTCo5932CFTTFahrenheit scale F98.6 C37.0 K 15.310ooF 212C100 K 15.373ooThe Celsius and Fahrenheit ScalesTemperatureCFBoiling point of

6、water 100 212Normal body temperature 37.098.6Accepted comfort level 2068Freezing point of water 032Zero of Fahrenheit scale 180Scales coincide 4040Thermal ExpansionVolume Expansion:TLLTVV3Linear Expansion: coefficient of linear expansion, with unit of /oC: coefficient of volume expansion, with unit

7、of /oCCoefficient of linear expansionSubstance (106/C)Substance (106/C)Ice (at 0C)51Steel11Lead29Glass (ordinary)9Aluminum23Glass (Pyrex)3.2Brass19Diamond1.2Copper17Invar（不胀钢）（不胀钢）0.7Concrete12Fused quartz0.5Thermal ExpansionThermal ExpansionThe wonderful behavior of water at 4 0CTemperature and Hea

8、tAbsorbed Q 0 Q = 0 Released Q 0: system to outsideW 0, release Q 0, work to the system W 0The law of conservation of energy:“The total energy of an isolated system cannot change. The first law of thermodynamics is an extension of the law of conservation of energy.The First Law of Thermodynamics Som

9、e Special Cases of the First Law of Thermodynamics 1 : Adiabatic (绝热绝热 processWEintWEQint0QWEint2： Constant-volume process0dVWEQintQEint0pdVWQEintSome Special Cases of the First Law of Thermodynamics 3： Cyclical循环的循环的 processes0intEWEQintQW Heat Engine Some Special Cases of the First Law of Thermody

10、namics 4： Free expansion Some Special Cases of the First Law of Thermodynamics 0intE0WQnot in thermal equilibrium Sample ProblemMJ 169. 0ifVVVVVVpdVppdVWfifiMJ 260. 2kJ/kg2256mLQLVVMJ 09. 2intWQEWQ Problem: 5-3 m3 as a liquid to 1.671 m3 as steam. (a) How much work is done by the system during this

11、process? (b) How much energy is transferred as heat during the process?(c) What is the change in the systems internal energy during the process?Solution: (a)(b)(c)Heat Transfer Mechanisms - Conduction传导传导 - Convection (对流对流 - Radiation辐射辐射Heat Transfer Mechanisms Thermal conductionThermal conduction

12、: (take the poker as an example) The vibration amplitudes of the atoms and electrons of the metal at the fire end of the poker become relatively large because of the high temperature of their environment. These increased vibrational amplitudes, and thus the associated energy, are passed along the po

13、ker, from atom to atom, during collisions between adjacent atoms. In this way, a region of rising temperature extends itself along the poker to the handle atoms vibration. LTTkAtQPCHcondConduction rate:k : thermal conductivityA: face areaL: thicknessThermal ConductivitySubstancek (W/m.K)MetalsStainl

14、ess steel14Lead35Iron67Brass109Aluminum235Copper401Silver428GasesAir(dry)0.026Helium0.15Hydrogen0.18Building materialPolyurethane foam (聚氨酯)0.024Rock wool0.043Fiberglass0.048White pine0.11Window glass1.0Thermal Resistance to Conduction (R-Value)kLR R-value:Application: Something that has a high R-va

15、lue is a good thermal insulator.Thermal Conduction Through a Composite SlabS t e a d y - s t a t e p ro c e s s : t h e temperature T everywhere in the slab and the rates of energy transfer Pcond do not change with time.kLTTAkLkLTTAPLkLkTLkTLkTLTTAkLTTAkPCHCHcondHCXCXXHcond2211122112211122Convection: play an important role in our lifeHeat Transfer Mechanisms Thermal convectionConvection: play an important role in our lifeHeat Transfer Mechanisms Thermal RadiationThermal radiation: via electromagnetic waves.)