17p1物理春季第7次课thermal physics

APPhysics2:Lecture4.HeatandthermalHeatisdefinedasthermalenergythat’stransmittedfromonebodytoanother.heat是过程量thermalenergyAnobjectcancontainthermalenergybutdoesn’tcontainTemperatureisameasureoftheconcentrationofanobject’sinternalthermalenergy摄氏度DegreesCelsius zesat0℃andboilsat100开氏度DegreesKelvinsabsolutetemperaturescale(always zesat273.15Kandboilsat373.15AkelvinisequalinsizetoaCelsiusmechanicalequivalentofheat热功当量(焦耳.Themechanicalequivalentofheatwasaconceptthathadanimportantpartinthedevelopmentandacceptanceoftheconservationof.PhysicalChangeDuetoHeatPhysicalChangeDuetoHeatWhenasubstanceabsorbsorgivesoffheat,oneoftwothingscanhappen:thetemperatureofthesubstancecanchangephasethesubstancecanundergophase相变三角形单词要牢记 QQ=Llatentheatoftransformation相变潜热Q=(J/kgKNamesofLatentThermalCoefficientofLinearLinearcoefficientofexpansionα)Unit:K-1(α=10-4/K代表每升⾼1K,⻓度增⻓β≈β≈VolumetriccoefficientofexpansionβUnit:K-1(β=10-4/K代表每升⾼1K,体积增⼤Heatcanbetransferredfromoneobjecttoanotherbythreedifferentmethods:conduction,convection,andradiation.热传递的三种方式传导对流瓶口软木 隔绝热水与冷空气,减少 双层瓶胆之间的空隙抽成真空，减少 RateofHeatTransferfortherateofheattransfer(H),whichistheenergytransferredtothesystem(Q)perunittime(Δt)measuredinJ/s,orwatts,dependson:temperaturedifferenceacrosstheobjectthethecross-sectionalareaoftheobjectthelengthoftheobjectthethermalconductivityofthematerial TheKineticTheoryofBrownianmovement:thecontinuousrandomstraight-linemotionofgasorliquidmolecules.[动画Thepressureofagasonitscontainerisduetothecollisionsofthegasmoleculeswiththewallsofthecontainer压强单位Pa 常数:1mole气体里的分子数IdealGas P:V体积T: 3.分子之间、分子与器壁之间的碰撞，不造成动能损失(elastic IdealGasLaw(重点不能画PvsV的图必须画Pvs.1/V的图不能只测定⼀个温度下P/V的变化要测定多个温度下P和V的变化关系.例如将T设定在300K/320K/340K/360K,测4个系列的P和V如果4条直线都吻合得很好且斜率与T成正比,则可证明Internal(1)分⼦⽆规则运动动能(kinetic(2)分⼦势能(potential(3)分⼦内部以及原⼦核内部各种形式能量(例如化学键能分⼦平均动能与绝对温度成正比计算时注意使⽤Kevinvrms:thesquarerootoftheaverageofthesquareofv,iscalled 补充知识点Maxwell温度升高曲线变得扁平(thecurveflattens),同时峰值右移(theumshiftstohigherspeeds).0thLawofThermalThermalequilibrium热平衡第零定律IfObjects1and2areeachinthermalequilibriumwithObject3,thenObjects1and2areinthermalequilibriumwitheachother.1stLawof⼀是给它传热(Q),⼆是对它做功WorkdoneONthegasExpansion膨胀Compression压缩 P-V isobaric等压isothermal等温P-V 第1步通过PVnRT分析ΔTΔU正比于第2步通过曲线⽅向判断W的正负通过曲线下围面积分析W的⼤⼩.第3步通过ΔUWQ分析Q除非题目给出,否则Q总是最后才得到).WWQAdiabatic等温膨胀曲线(isothermalexpansioncurve)的下方AnidealgascanmovefromState1toState2viathreedifferentpossiblepaths:PathA,PathB,andPathC.Whichofthefollowingstatementsaretrue?Selecttwoanswers.Changeintemperatureisthesameforallthreepaths.Heatabsorbedisthesameforthree(A)and(D)aretrue,asboththechangeintemperatureandthechangeininternalenergyarepathindependent.Workdonebythegasis(A)and(D)aretrue,asboththechangeintemperatureandthechangeininternalenergyarepathindependent.ChangeininternalenergyissameforallthreeOnemoleofanidealgasundergoesaseriesofchangesinpressureandvolumeasitfollowspathABCAonthePVdiagram.UsingthePVdiagram,findthetemperatureofthegasateachpoint,thenfillintheinformationtablebyfindingthechangeininternalenergy,workdoneon,andheataddedtothegasforeach4majorprocessIn2ndLawofEntropy 程度(disorder)的度量, smaller larger表述一Entropyinanisolatedsystemwillnever 不减少(ΔS≥温度变化与熵的变化:温度增加,温度变化与熵的变化:温度增加,⼤,更加⽆序⾼温物体低温物体系统

系统内能没有改变(EABEA表述二“Heatwillnotflowspontaneouslyfromacolderbodytoawarmerbody.”热不会自发从低温物体传到高温物体.热⾃发从低温传到⾼温,并不违背第⼀定律,表述三:“heatenergycannotbetransformedcomple yintomechanicalwork.”不能将热100%转化为功.100%的热效率,并不违背第⼀定律,即使没有摩擦损耗,热效率也不可能达到Ifnoworkisdoneonasystem,entropyspontaneouslyreachesa HeatHeatHeatengineand热机Aheatenginetransformsheatathightemperatureintomechanicalene