APPhysics2:Lecture4.HeatandthermalHeatisdefinedasthermalenergythat’stransmittedfromonebodytoanother.heat是過程量thermalenergyAnobjectcancontainthermalenergybutdoesn’tcontainTemperatureisameasureoftheconcentrationofanobject’sinternalthermalenergy攝氏度DegreesCelsius zesat0℃andboilsat100開氏度DegreesKelvinsabsolutetemperaturescale(always zesat273.15Kandboilsat373.15AkelvinisequalinsizetoaCelsiusmechanicalequivalentofheat熱功當(dāng)量(焦耳.Themechanicalequivalentofheatwasaconceptthathadanimportantpartinthedevelopmentandacceptanceoftheconservationof.PhysicalChangeDuetoHeatPhysicalChangeDuetoHeatWhenasubstanceabsorbsorgivesoffheat,oneoftwothingscanhappen:thetemperatureofthesubstancecanchangephasethesubstancecanundergophase相變?nèi)切螁卧~要牢記 QQ=Llatentheatoftransformation相變潛熱Q=(J/kgKNamesofLatentThermalCoefficientofLinearLinearcoefficientofexpansionα)Unit:K-1(α=10-4/K代表每升?1K,?度增?β≈β≈VolumetriccoefficientofexpansionβUnit:K-1(β=10-4/K代表每升?1K,體積增?Heatcanbetransferredfromoneobjecttoanotherbythreedifferentmethods:conduction,convection,andradiation.熱傳遞的三種方式傳導(dǎo)對流瓶口軟木 隔絕熱水與冷空氣,減少 雙層瓶膽之間的空隙抽成真空，減少 RateofHeatTransferfortherateofheattransfer(H),whichistheenergytransferredtothesystem(Q)perunittime(Δt)measuredinJ/s,orwatts,dependson:temperaturedifferenceacrosstheobjectthethecross-sectionalareaoftheobjectthelengthoftheobjectthethermalconductivityofthematerial TheKineticTheoryofBrownianmovement:thecontinuousrandomstraight-linemotionofgasorliquidmolecules.[動(dòng)畫Thepressureofagasonitscontainerisduetothecollisionsofthegasmoleculeswiththewallsofthecontainer壓強(qiáng)單位Pa 常數(shù):1mole氣體里的分子數(shù)IdealGas P:V體積T: 3.分子之間、分子與器壁之間的碰撞，不造成動(dòng)能損失(elastic IdealGasLaw(重點(diǎn)不能畫PvsV的圖必須畫Pvs.1/V的圖不能只測定?個(gè)溫度下P/V的變化要測定多個(gè)溫度下P和V的變化關(guān)系.例如將T設(shè)定在300K/320K/340K/360K,測4個(gè)系列的P和V如果4條直線都吻合得很好且斜率與T成正比,則可證明Internal(1)分??規(guī)則運(yùn)動(dòng)動(dòng)能(kinetic(2)分?勢能(potential(3)分?內(nèi)部以及原?核內(nèi)部各種形式能量(例如化學(xué)鍵能分?平均動(dòng)能與絕對溫度成正比計(jì)算時(shí)注意使?Kevinvrms:thesquarerootoftheaverageofthesquareofv,iscalled 補(bǔ)充知識點(diǎn)Maxwell溫度升高曲線變得扁平(thecurveflattens),同時(shí)峰值右移(theumshiftstohigherspeeds).0thLawofThermalThermalequilibrium熱平衡第零定律IfObjects1and2areeachinthermalequilibriumwithObject3,thenObjects1and2areinthermalequilibriumwitheachother.1stLawof?是給它傳熱(Q),?是對它做功WorkdoneONthegasExpansion膨脹Compression壓縮 P-V isobaric等壓isothermal等溫P-V 第1步通過PVnRT分析ΔTΔU正比于第2步通過曲線?向判斷W的正負(fù)通過曲線下圍面積分析W的??.第3步通過ΔUWQ分析Q除非題目給出,否則Q總是最后才得到).WWQAdiabatic等溫膨脹曲線(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 不減少(ΔS≥溫度變化與熵的變化:溫度增加,溫度變化與熵的變化:溫度增加,?,更加?序?溫物體低溫物體系統(tǒng)

系統(tǒng)內(nèi)能沒有改變(EABEA表述二“Heatwillnotflowspontaneouslyfromacolderbodytoawarmerbody.”熱不會(huì)自發(fā)從低溫物體傳到高溫物體.熱?發(fā)從低溫傳到?溫,并不違背第?定律,表述三:“heatenergycannotbetransformedcomple yintomechanicalwork.”不能將熱100%轉(zhuǎn)化為功.100%的熱效率,并不違背第?定律,即使沒有摩擦損耗,熱效率也不可能達(dá)到Ifnoworkisdoneonasystem,entropyspontaneouslyreachesa HeatHeatHeatengineand熱機(jī)Aheatenginetransformsheatathightemperatureintomechanicalene