Introductory Physics - · Assistant Professor of Physics ... Mastering Physics Online ... First Law of Thermodynamics Heat Engines Heat Pumps, Refrigerators ...

IntroductoryPhysics

PHYS101

Dr RichardH.CyburtOfficeHoursAssistantProfessorofPhysics

Myoffice:402cintheScienceBuilding

Myphone:(304)384-6006

Myemail:[email protected]

Inpersonoremailisthebestwaytogetaholdofme.

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Checkmyscheduleonmyofficedoor.

PHYS101

PHYS101:IntroductoryPhysicsLecture:8:00-9:15am,TRScienceBuilding400Lab1:3:00-4:50pm,FScienceBuilding304

Lab2:1:30-3:20pm,MScienceBuilding304



PHYS101

MasteringPhysicsOnlineGotoHYPERLINK"http://www.masteringphysics.com."www.masteringphysics.com.◦ UnderRegisterNow,selectStudent.◦ Confirmyouhavetheinformationneeded,thenselectOK!Registernow.

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PHYS101

Midterm3Thursday,Oct278:00-9:15amS400

Chapters8-11,onlywhatwehavecoveredinlecture

ReviewSession:Wednesday,Oct267:00-9:00pmS300

Bringquestions!!!(HW,Lab,EndofChapter,Workbook)

Allowedhalfsheetpaperofformulaandcalculator

PHYS101

IntroductoryPhysics

PHYS101

PHYS101

DouglasAdamsHitchhiker’sGuidetotheGalaxy

You’realreadyknowphysics!Youjustdon’tnecessarilyknowtheterminologyandlanguageweuse!!!

PhysicsofNASCARPhysicsofAngerBirds

PHYS101

FrommywifeandtheOEDshiok, int. and adj.[‘ Expressingadmirationorapproval:‘cool!’‘great!’’]

Pronunciation: Brit. /ˈʃiːɒk/, U.S. /ˈʃiɑk/, SingaporeandMalaysianEnglish /ʃok/

Origin:A borrowingfromMalay.Etymon:Malay syok.

Etymology: < Malay syok pleasing,attractive< Persian šoḵ cheerful,spirited,ultimately< Arabic(compare šawq desire,passion).

SingaporeEnglish. A.int. Expressingadmirationorapproval:‘cool!’‘great!’1977 NewNation(Singapore) 26May 19/2 Fantas.Ooh-la-la.Phew-whew.Wowie.Shiok.Jazzy,man.Beaut.

1992 StraitsTimes(Singapore)(Nexis) 15May, English-educatedSingaporeansknowthatthereisanAhKow withinthemdyingtoburstoutwithaproclamative wah shiok man!

1995 StraitsTimes(Singapore)(Nexis) 24Apr., Wah lau,ifgotsuchadictionary,damngood,y'know.Youread,surecanlaugh.Shiok man.

2006 Edge(Malaysia)(Nexis) 2Jan., Goldtaps,goldbathtub,golddinnertable...Wah shiok.

B.adj. 1. Offood,ameal,etc.:delicious,superb.1978 StraitsTimes(Singapore) 8July 16/1(advt.) Helppreservetheessenceof‘shiok’cooking!

PHYS101

Inclass!!

PHYS101

Thislecturewillhelpyouunderstand:Temperature,ThermalEnergyandHeatFirstLawofThermodynamicsHeatEnginesHeatPumps,Refrigerators,andAirConditionersEntropyandtheSecondLawofThermodynamicsSystems,EnergyandEntropy

PHYS101

Section11.3Temperature,ThermalEnergy,andHeat

©2015PearsonEducation,Inc.

AnAtomicViewofThermalEnergyandTemperatureThethermalenergyofanidealgasisequaltothetotalkineticenergyofthemovingatomsinthegas.


[InsertFigure11.8]

AnAtomicViewofThermalEnergyandTemperatureHeatingagascausestheatomstomovefaster,increasingthethermalenergyofthegas.

Heatingalsocausesanincreaseintemperature.

Thetemperatureofanidealgasisameasureoftheaveragekineticenergyoftheatomsthatmakeupthegas.


QuickCheck11.6

Twocontainersofthesamegas(whichweassumetobeideal)havethefollowingmassesandtemperatures:

Whichboxhasthegaswiththelargestthermalenergy?


AB

QuickCheck11.6


Whichboxhasthegaswiththelargestthermalenergy?


AB

QuickCheck11.5


Whichboxhasthegaswiththelargestaveragekineticenergypermolecule?


QuickCheck11.5


Whichboxhasthegaswiththelargestaveragekineticenergypermolecule?


QuickCheck11.10

100Jisaddedtoasampleofidealgasasheat.Thegasthenexpandsagainstapiston,doing70Jofwork.Duringthisprocess

◦ Thetemperatureofthegasincreases.◦ Thetemperatureofthegasdecreases.◦ Thetemperatureofthegasstaysthesame.


QuickCheck11.10

100Jisaddedtoasampleofidealgasasheat.Thegasthenexpandsagainstapiston,doing70Jofwork.Duringthisprocess

◦ Thetemperatureofthegasincreases.◦ Thetemperatureofthegasdecreases.◦ Thetemperatureofthegasstaysthesame.


QuickCheck11.7

Asteadyforcepushesinthepistonofawell-insulatedcylinder.Inthisprocess,thetemperatureofthegas

◦ Increases.◦ Staysthesame.◦ Decreases.◦ There’snotenoughinformationtotell.


QuickCheck11.7

Asteadyforcepushesinthepistonofawell-insulatedcylinder.Inthisprocess,thetemperatureofthegas

◦ Increases.◦ Staysthesame.◦ Decreases.◦ There’snotenoughinformationtotell.


First law: Q + W = ΔEth

No heat flows (well insulated) ...... but work is done on the gas.

Work increases the gas’s thermal energy and with it the temperature.

TemperatureScalesTheCelsiusscaleisdefinedsothatthefreezingpointofwateris0°C.TheFahrenheitscaleisrelatedtotheCelsiusscale:


TemperatureScalesFortheKelvinscale,zerodegreesisthepointatwhichthekineticenergyoftheatomsiszero.Kineticenergyisalwayspositive,sozeroonthisscaleisanabsolutezero.AlltemperaturesontheKelvinscalearepositive,soitisoftencalledtheabsolutetemperaturescale.Theunitsare“kelvin”(K).


TemperatureScalesThespacingbetweendivisionsontheKelvinscaleisthesameasthatontheCelsiusscale.

Absolutezerois–273°C:


QuickCheck11.3

Whichisthelargestincreaseoftemperature?

◦ Anincreaseof1°F◦ Anincreaseof1°C◦ Anincreaseof1K◦ BothBandC,whicharethesameandlargerthanA◦ A,B,andCareallthesameincrease.


QuickCheck11.3

Whichisthelargestincreaseoftemperature?

◦ Anincreaseof1°F◦ Anincreaseof1°C◦ Anincreaseof1K◦ BothBandC,whicharethesameandlargerthanA◦ A,B,andCareallthesameincrease.


QuickCheck11.4

Whichisthecorrectrankingoftemperatures,fromhighesttolowest?

◦ 300°C>300K>300°F◦ 300°C>300°F>300K◦ 300K>300°F>300°C◦ 300K>300°C>300°F◦ 300°F>300K>300°C


QuickCheck11.4

Whichisthecorrectrankingoftemperatures,fromhighesttolowest?

◦ 300°C>300K>300°F◦ 300°C>300°F>300K◦ 300K>300°F>300°C◦ 300K>300°C>300°F◦ 300°F>300K>300°C


WhatIsHeat?Thermodynamicsisthestudyofthermalenergyandheatandtheirrelationshipstootherformsofenergyandenergytransfer.Heatisenergytransferredbetween twoobjectsbecauseofatemperaturedifferencebetweenthem.Heat(Q)alwaysflowsfromthehotterobjecttothecoolerone.


[InsertFigure11.11.]

AnAtomicModelofHeatThermalenergyistransferredfromthefastermovingatomsonthewarmersidetotheslowermovingatomsonthecoolerside.

Thetransferwillcontinueuntilastablesituation,orthermalequilibrium,isreached.


AnAtomicModelofHeatTwosystemsplacedinthermalcontactwilltransferthermalenergyfromhottocolduntiltheirfinaltemperaturesarethesame.


QuickCheck11.2Consideryourbodyasasystem.Yourbodyis“burning”energyinfood,butstayingataconstanttemperature.Thismeansthat,foryourbody,

◦ Q >0◦ Q =0◦ Q <0


QuickCheck11.2Consideryourbodyasasystem.Yourbodyis“burning”energyinfood,butstayingataconstanttemperature.Thismeansthat,foryourbody,

◦ Q >0◦ Q =0◦ Q <0


QuickCheck11.9

AcylinderofgashasafrictionlessbuttightlysealedpistonofmassM.Smallmassesareplacedontothetopofthepiston,causingittoslowlymovedownward.Awaterbathkeepsthetemperatureconstant.Inthisprocess◦ Q >0◦ Q =0◦ Q <0◦ There’snotenoughinformationtosayanythingabouttheheat.


QuickCheck11.9AcylinderofgashasafrictionlessbuttightlysealedpistonofmassM.Smallmassesareplacedontothetopofthepiston,causingittoslowlymovedownward.Awaterbathkeepsthetemperatureconstant.Inthisprocess◦ Q >0◦ Q =0◦ Q <0◦ There’snotenoughinformationtosayanythingabouttheheat.


DEth = W + Q0 + –

No temperature change Energy flows out to the water to keep the temperature from changing

Section11.4TheFirstLawofThermodynamics


TheFirstLawofThermodynamicsSystemsthatarenotmovingandarenotchangingchemically,butwhosetemperaturescanchange,aretheprovinceofthermodynamics.


Example11.9EnergytransfersinablenderIfyoumixfoodinablender,theelectricmotordoesworkonthesystem,whichconsistsofthefoodinsidethecontainer.Thisworkcannoticeablywarmupthefood.Supposetheblendermotorrunsatapowerof250Wfor40s.Duringthistime,2000Jofheatflowfromthenow-warmerfoodtoitscoolersurroundings.Byhowmuchdoesthethermalenergyofthefoodincrease?


Example11.9Energytransfersinablender(cont.)

PREPARE Onlythethermalenergyofthesystemchanges,sowecanusethefirstlawofthermodynamics,Equation11.8.Wecanfindtheworkdonebythemotorfromthepoweritgeneratesandthetimeitruns.



SOLVE FromEquation10.22,theworkdoneisW =P ∆t =(250W)(40s)=10,000J.Becauseheatleaves thesystem,itssignisnegative,soQ =-2000J.Thenthefirstlawofthermo-dynamicsgives



ASSESS Itseemsreasonablethattheworkdonebythepowerfulmotorrapidlyincreasesthethermalenergy,whilethermalenergyonlyslowlyleaksoutasheat.Theincreasedthermalenergyofthefoodimpliesanincreasedtemperature.Ifyourunablenderlongenough,thefoodcanactuallystarttosteam,asthephotoshows.


Energy-TransferDiagramsAnenergyreservoir isanobjectorapartoftheenvironmentsolargethatitstemperaturedoesnotnoticeablychangewhenheatistransferredbetweenthesystemandthereservoir.


Energy-TransferDiagramsAreservoirathighertemperaturesisahotreservoir(TH),andoneatlowertemperaturesisacoldreservoir(TC).

QH andQCaretheamountofheattransferredtoorfromahotandcoldreservoir,respectively.

Bydefinition,QH andQC arepositivequantities.


QuickCheck11.11

Alarge–20°Cicecubeisdroppedintoasuper-insulatedcontainerholdingasmallamountof5°Cwater,thenthecontainerissealed.Tenminuteslater,isitpossiblethatthetemperatureoftheicecubewillbecolderthan–20°C?

◦ Yes◦ No◦ Maybe.Itwoulddependonotherfactors.


QuickCheck11.11

Alarge–20°Cicecubeisdroppedintoasuper-insulatedcontainerholdingasmallamountof5°Cwater,thenthecontainerissealed.Tenminuteslater,isitpossiblethatthetemperatureoftheicecubewillbecolderthan–20°C?

◦ Yes◦ No◦ Maybe.Itwoulddependonotherfactors.


Energy-TransferDiagramsEnergy-transferdiagrams:Thehotreservoirisdrawnatthetop,thecoldatthebottom,andthesystem(thecopperbar)betweenthem.

The“pipes”connectthereservoirandsystemandshowtheenergytransfers.


Energy-TransferDiagramsSpontaneoustransfersgoinonedirectiononly:fromhottocold.


Energy-TransferDiagramsSpontaneoustransfersgoinonedirectiononly:fromhottocold.


OnlytheFonz radiates“Coolness”!

ConceptualExample11.10EnergytransfersandthebodyWhy—inphysicsterms—isitmoretaxingonthebodytoexerciseinveryhotweather?REASON Yourbodycontinuouslyconvertschemicalenergytothermalenergy,aswehaveseen.Inordertomaintainaconstantbodytemperature,yourbodymustcontinuouslytransferheattotheenvironment.Thisisasimplematterincoolweatherwhenheatisspontaneouslytransferredtotheenvironment,butwhentheairtemperatureishigherthanyourbodytemperature,yourbodycannotcoolitselfthiswayandmustuseothermechanismstotransferthisenergy,suchasperspiring.Thesemechanismsrequireadditionalenergyexpenditure.ASSESS Strenuousexerciseinhotweathercaneasilyleadtoariseinbodytemperatureifthebodycannotexhaustheatquicklyenough.


Section11.5HeatEngines


HeatEnginesThermalenergyisnaturallytransferredfromahotreservoirtoacoldreservoir.

Aheatenginetakessomeoftheenergyasitistransferredandconvertsittootherforms.


HeatEnginesTheheatenginetakesenergyasheatfromthehotreservoir,turnssomeintousefulwork,andexhauststhebalanceaswasteheatintothecoldreservoir.


HeatEngines


HeatEnginesMostoftheenergythatyouusedailycomesfromtheconversionofthatenergyintootherforms.


Text:p.333

HeatEnginesMostoftheenergythatyouusedailycomesfromtheconversionofthatenergyintootherforms.


Text:p.333

HeatEnginesTheworkextractedisequaltothedifferencebetweentheheatenergytransferredfromthehotreservoirandtheheatexhaustedintothecoldreservoir:

Wout =QH– QC

Theheatengine’sefficiencyis


HeatEnginesNoheatenginecanoperatewithoutexhaustingsomefractionoftheheatintoacoldreservoir.


HeatEnginesThemaximumefficiencyisfixedbythesecondlawofthermodynamics:


QuickCheck11.14

Thefollowingpairsoftemperaturesrepresentthetemperaturesofhotandcoldreservoirsforheatengines.Whichheatenginehasthehighestpossibleefficiency?

◦ 300°C,30°C◦ 250°C,30°C◦ 200°C,20°C◦ 100°C,10°C◦ 90°C,0°C


QuickCheck11.14

Thefollowingpairsoftemperaturesrepresentthetemperaturesofhotandcoldreservoirsforheatengines.Whichheatenginehasthehighestpossibleefficiency?

◦ 300°C,30°C◦ 250°C,30°C◦ 200°C,20°C◦ 100°C,10°C◦ 90°C,0°C


QuickCheck11.12Theefficiencyofthisheatengineis

◦ 1.00◦ 0.60◦ 0.50◦ 0.40◦ 0.20


QuickCheck11.12Theefficiencyofthisheatengineis

◦ 1.00◦ 0.60◦ 0.50◦ 0.40◦ 0.20


Example11.11TheefficiencyofanuclearpowerplantEnergyfromnuclearreactionsinthecoreofanuclearreactorproduceshigh-pressuresteamatatemperatureof290°C.

Afterthesteamisusedtospinaturbine,itiscondensed(byusingcoolingwaterfromanearbyriver)backtowaterat20°C.

Theexcessheatisdepositedintheriver.

Thewateristhenreheated,andthecyclebeginsagain.

Whatisthemaximumpossibleefficiencythatthisplantcouldachieve?


Example11.11Theefficiencyofanuclearpowerplant(cont.)PREPARE Anuclearpowerplantisaheatengine,withenergytransfersasillustratedinFigure11.18a.QH istheheatenergytransferredtothesteaminthereactorcore.TH isthetemperatureofthesteam,290°C.Thesteamiscooledandcondensed,andtheheatQC isexhaustedtotheriver.Theriveristhecoldreservoir,soTC is20°C.Inkelvin,thesetemperaturesare


Example11.11Theefficiencyofanuclearpowerplant(cont.)SOLVEWeuseEquation11.10tocomputethemaximumpossibleefficiency:

ASSESS Thisisthemaximumpossibleefficiency.Therearepracticallimitationsaswellthatlimitrealpowerplants,whethernuclearorcoal- orgas-fired,toanefficiencye ≈0.35.Thismeansthat65%oftheenergyfromthefuelisexhaustedaswasteheatintoariverorlake,whereitmaycauseproblematicwarminginthelocalenvironment.


Section11.6HeatPumps,Refrigerators,andAirConditioners


HeatPumpsTransferringheatenergyfromacoldreservoirtoahotreservoiristhejobofaheatpump.


HeatPumpsForheatpumps,insteadofefficiencywecomputethecoefficientofperformance(COP).


HeatPumpsIfweusetheheatpumpforcooling,wedefineCOPas


Ifweusetheheatpumpforheating,wedefineCOPas

Inbothcases,alargercoefficientofperformancemeansamoreefficientheatpump.

HeatPumps


QuickCheck11.15

APeltier coolerisaheatpumpthatcanbesettoeithercoolorheatitscontents.Onesuchcooleruses100Wofinputpowerwhetherheatingorcooling.Whichisgreater,itscoefficientofperformanceforcoolingoritscoefficientofperformanceforheating?

◦ Cooling◦ Heating◦ Thetwocoefficientsarethesame.


WinHeat!pump

QH

QC

100 J/s

QuickCheck11.15

APeltier coolerisaheatpumpthatcanbesettoeithercoolorheatitscontents.Onesuchcooleruses100Wofinputpowerwhetherheatingorcooling.Whichisgreater,itscoefficientofperformanceforcoolingoritscoefficientofperformanceforheating?

◦ Cooling◦ Heating◦ Thetwocoefficientsarethesame.


WinHeat!pump

QH

QC

100 J/s

QuickCheck11.13

Thecoefficientofperformanceofthisrefrigeratoris

◦ 0.40◦ 0.60◦ 1.50◦ 1.67◦ 2.00


QuickCheck11.13

Thecoefficientofperformanceofthisrefrigeratoris

◦ 0.40◦ 0.60◦ 1.50◦ 1.67◦ 2.00


Example11.12CoefficientofperformanceofarefrigeratorTheinsideofyourrefrigeratorisapproximately0°C.Heatfromtheinsideofyourrefrigeratorisdepositedintotheairinyourkitchen,whichhasatemperatureofapproximately20°C.Attheseoperatingtemperatures,whatisthemaximumpossiblecoefficientofperformanceofyourrefrigerator?

PREPARE Thetemperaturesofthehotsideandthecoldsidemustbeexpressedinkelvin:


Example11.12Coefficientofperformanceofarefrigerator(cont.)SOLVEWeuseEquation11.11tocomputethemaximumcoefficientofperformance:

ASSESS Acoefficientofperformanceof13.6meansthatwepump13.6Jofheatforanenergycostof1J.Duetopracticallimitations,thecoefficientofperformanceofanactualrefrigeratoristypically≈5.Otherfactorsaffecttheoverallefficiencyoftheappliance,includinghowwellinsulateditis.


Section11.7EntropyandtheSecondLawofThermodynamics


EntropyandtheSecondLawofThermodynamicsThespontaneoustransferofheatfromhottocoldisanirreversible process;itcanhappeninonlyonedirection.

Thesecondlawofthermodynamics preventsthespontaneoustransferofheatfromcoldtohot.


ReversibleandIrreversibleProcessesAtthemicroscopiclevel,collisionsbetweenmoleculesarereversible.


ReversibleandIrreversibleProcessesAtthemacroscopiclevel,collisionsareusuallyirreversible.


WhichWaytoEquilibrium?IfBox1hasmoreballsthanBox2,andyourandomlypickanyballtoswitchboxes,thereisahigherprobabilityyouwillpickaballfromBox1.

ThereisanetflowofballsmovingfromBox1toBox2untilequilibriumisreached.


WhichWaytoEquilibrium?Theprocessisreversible(aballcanbemovedbacktoBox1).

ThestatisticsoflargenumbersmakeitoverwhelminglylikelythatthesystemwillevolvetowardastateinwhichN1≈N2.


WhichWaytoEquilibrium?Systemsreachthermalequilibriumbecauseequilibriumisthemostprobablestateinwhichtobe.

Reversiblemicroscopiceventsleadtoirreversiblemacroscopicbehaviorbecausesomemacroscopicstatesarevastlymoreprobablethanothers.


Order,Disorder,andEntropyEntropy quantifiestheprobabilitythatacertainstateofasystemwilloccur.

Entropyincreasesastwosystemswithinitiallydifferenttemperaturesmovetowardthermalequilibrium.


Order,Disorder,andEntropy


Order,Disorder,andEntropyThesecondlawofthermodynamicstellsusthatanisolatedsystemevolvessuchthat:◦ Orderturnsintodisorderandrandomness.◦ Informationislostratherthangained.◦ Thesystem“runsdown”asotherformsofenergyaretransformedintothermalenergy.


EntropyandThermalEnergyInaverycold,movingbaseball,alloftheatomsaremovinginthesamedirectionandsamespeed.Ithaslowentropy.

Inastationaryheliumballoon,theatomsaredisorganizedandhaverandommotion(thermalenergy).Ithashighentropy.


EntropyandThermalEnergyWhenanotherformofenergyisconvertedintothermalenergy,thereisanincreaseinentropy.

Thisiswhyconvertingthermalenergyintootherformscannotbedonewith100%efficiency.


QuickCheck11.16

Alarge–20°Cicecubeisdroppedintoasuper-insulatedcontainerholdingasmallamountof5°Cwater,thenthecontainerissealed.Tenminuteslater,thetemperatureoftheice(andanywaterthathasmeltedfromtheice)willbewarmerthan–20°C.Thisisaconsequenceof

◦ Thefirstlawofthermodynamics.◦ Thesecondlawofthermodynamics.◦ Thethirdlawofthermodynamics.◦ Boththefirstandthesecondlaws.◦ Joule’slaw.


QuickCheck11.16

Alarge–20°Cicecubeisdroppedintoasuper-insulatedcontainerholdingasmallamountof5°Cwater,thenthecontainerissealed.Tenminuteslater,thetemperatureoftheice(andanywaterthathasmeltedfromtheice)willbewarmerthan–20°C.Thisisaconsequenceof

◦ Thefirstlawofthermodynamics.◦ Thesecondlawofthermodynamics.◦ Thethirdlawofthermodynamics.◦ Boththefirstandthesecondlaws.◦ Joule’slaw.


Section11.8Systems,Energy,andEntropy


TheConservationofEnergyandEnergyConservationEnergycannotbecreatedordestroyed,butwhenenergyistransformed,someofitisconvertedtothermalenergy.Thechangeisirreversible.

To“conserveenergy”wemustconcentrateonefficiency.


EntropyandLifeLifeseemstoviolatethesecondlawofthermodynamics:◦ Plantsgrowfromsimpleseedstocomplexentities.

◦ Single-celledfertilizedeggsgrowintocomplexadultorganisms.

◦ Overthelastbillionyears,lifehasevolvedfromunicellularorganismstocomplexforms.


EntropyandLifeThesecondlawofthermo-dynamicsonlyappliestoisolatedsystems:systemsthatdonotexchangeenergywiththeirenvironment.


EntropyandLifeYourbodyisnotanisolatedsystem.

Theentropyofyourbodyisapproximatelythesame,buttheentropyoftheenvironmentisincreasingduetothermalenergyfromyourbody.


Introductory Physics - · Assistant Professor of Physics ... Mastering Physics Online ... First Law of Thermodynamics Heat Engines Heat Pumps, Refrigerators ...

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