复旦大学《大学物理》课件（英文）-第21章 Temperature(1).pdf

Chapter 21 Temperature21-1 Temperature and thermal equilibrium1.Thermal equilibrium(a)Adiabatic(绝热)(thermally insulating)Fig 21-1 shows two systems A and B,they are isolatedfrom one another and fromtheir environment,by whichwe mean that neitherenergy nor matter can enter or leave either system.Fig 21-1 ABATBTFor example,the systems may be surrounded by wall made of thick slabs of styrofoam(泡沫聚苯乙烯).(b)Diathermic(热透性),means thermally conducting(c)Thermal equilibriumWhen the two system are placed in contact through a diathermic wall,the passage of heat energy through the wall causes the properties of two system to change.The changes goes to until finally all measured properties of each system approach constant values.When this occurs,we say that the two systems are in thermal equilibriumwith each other.2.Zeroth law of thermodynamics“If system A and B are each in thermal equilibrium with a third system C,then A and B are in thermal equilibrium with each other”The zeroth law underlies the concept of temperature.3.TemperatureWhen two system are in thermal equilibrium we say that they have the same temperature.21-2 Temperature Scales（温标）1.Kelvin scales(T)The definition:The triple point(三相点)of water was set to be(in 1954):It is one of the seven base units of SI Units.Although there is no apparent limit to how high the temperature of a system can be,there is a limit to how low it can be.T 0 KK16.273=trTThree temperature scales are defined:Kelvin scale,Celsius scale,and Fahrenheit scale2.Celsius and Fahrenheit scales(a)Celsius scale(the centigrade scale):The normal freezing point of water is defined to be ;The normal boiling point of water is defined to be .The triple point of water is found to be (273.16K).(21-2)(b)Fahrenheit scale(21-3)c0c1003259+=CFTT15.273=TTCc01.0TC=25 TF=77 cFTC=38 TF=100 cF21-3 Measuring temperaturesBased on Kelvin scale.1.Any property of a substance that varies with temperature of the system can form the basis for a thermometer(温度表).T usually is some function of x,thermometric property.T*=f(x)The simplest way is to choose linear relationshipbetween T andx:,*axT=(21-5)where a is a constant.The constant a can be obtained by measuring xat the triple point of water.If it is at 273.16K,we have We express temperature in Eq(21-5)by T*rather than T because the temperature so measured will be“a device sensitive temperature”,not a universal one.trxtrxxKxT16.273)(*=trxxTa16.273*=(21-6)Sample problem 21-1The resistance of a certain coil of platinum wire increases by a factor of 1.392 between the triple point of water and the boiling point of water at atmospheric pressure.What temperature for the normal boiling point of water is measured by this thermometer?Solution:KRRTRTtrboiltrboil2.380)392.1)(16.273()(*=This value gives“platinum resistance temperature”of boiling water.Other thermometers will give different values.2.The constantvolume gas thermometerBulbcapillaryhmercury reservoirLevel markermano-meterFig 21-4trP2H2N2O0200400 600800T(K)Fig 21-5N2GasWe define an“ideal gas temperature scale”:(21-7)VtconstrPPPLimKTtr=tan0)16.273(In this context,we define an ideal gas to be a gas that would read the same temperature T at all pressure,with no need for extrapolation.21-4 Thermal expansionThe change in any linear dimension of the solid,such as its length,width,or thickness,is called“a linear expansion”(21-8)is the change in length;L is the length;is the change in temperature;is called the coefficient of linear expansion.TLTLL=1.Linear expansion2.We define the coefficient of volume expansion as(21-12)where V is the volume of a solid(or liquid),is the change in volume.TVV=VThe rail distorted due to the thermal expansion.21-5 The ideal gas1.Ideal gas that is a gas whose properties represent the limiting behavior of real gases at sufficiently low densities.2.For ideal gas,it has following property,to a good approximation:PV=NKT(21-13)Here N is the number of molecules contained in the volume V;K is a Boltzmann constant.trP2H2N2O0200400 600800T(K)Fig 21-5KJK/1038.123=T is expressed in KelvinsIt is often more useful to write Eq(21-13)in a slightly different:ANNn/=MolmoleculesNA/1002.623=nRTPV=(21-17)Eqs(21-13)and(21-17)are completely equivalent forms of the“ideal gas Law”.,the number of molesAKNR=,the moles gas constantKMolJR=/31.8Now,enjoy some cartoons!Students in lectureare apt to suffer from cognitive overloadMr Osborne,may I be excused?My brain is full.Often I think I teach just to ensure that my pupils get thebest exam grades so that my school meets its target.也是应试教育！No Sir,I meant why are we here on a Saturday?Very interesting,Jason,but Im pretty sure its been done.