BlackbodyRadiationPhotoelectricEffectWave-ParticleDuality黑体辐射的光电效应的波粒二象性

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1、BlackbodyRadiationPhotoelectricEffectWave-ParticleDualitysections30-1–30-4Physics1161:Lecture28EverythingcomesungluedThepredictionsof“classicalphysics”(Newton’slawsandMaxwell’sequations)aresometimesWRONG.classicalphysicssaysthatanatom’selectronsshouldfallintothenucleusandSTAYTHERE.Nochemistry,nob

2、iologycanhappen.classicalphysicssaysthattoastercoilsradiateaninfiniteamountofenergy:radiowaves,visiblelight,X-rays,gammarays,…ThesourceoftheproblemIt’snotpossible,even“intheory”toknoweverythingaboutaphysicalsystem.knowingtheapproximatepositionofaparticlecorruptsourabilitytoknowitsprecisevelocity(“H

3、eisenberguncertaintyprinciple”)Particlesexhibitwave-likeproperties.interferenceeffects!QuantumMechanics!AtverysmallsizestheworldisVERYdifferent!EnergycancomeindiscretepacketsEverythingisprobability;verylittleisabsolutelycertain.Particlescanseemtobeintwoplacesatsametime.Lookingatsomethingchangeshowi

4、tbehaves.Hotobjectsglow(toastercoils,lightbulbs,thesun).AsthetemperatureincreasesthecolorshiftsfromRedtoBlue.Theclassicalphysicspredictionwascompletelywrong!(Itsaidthataninfiniteamountofenergyshouldberadiatedbyanobjectatfinitetemperature.)BlackbodyRadiationBlackbodyRadiationSpectrumVisibleLight:~0.

5、4mmto0.7mmHighertemperature:peakintensityatshorterlBlackbodyRadiation:FirstevidenceforQ.M.MaxPlanckfoundhecouldexplainthesecurvesifheassumedthatelectromagneticenergywasradiatedindiscretechunks,ratherthancontinuously.The“quanta”ofelectromagneticenergyiscalledthephoton.Energycarriedbyasinglephotonis

6、E=hf=hc/Planck’sconstant:h=6.626X10-34JoulesecPreflights28.1,28.3Aseriesoflightbulbsarecoloredred,yellow,andblue.Whichbulbemitsphotonswiththemostenergy?Theleastenergy?Whichishotter?(1)stoveburnerglowingred(2)stoveburnerglowingorangePreflights28.1,28.3Aseriesoflightbulbsarecoloredred,yellow,andblue

7、.Whichbulbemitsphotonswiththemostenergy?Theleastenergy?Whichishotter?(1)stoveburnerglowingred(2)stoveburnerglowingorangeBlue!Lowestwavelengthishighestenergy.E=hf=hc/lRed!Highestwavelengthislowestenergy.Hott