作者	S.Brandt/等
出版社
出版时间	1998-03-01

特色：

片断：1.IntroductionThebasicfieldsofclassicalphysicsaremechanicsandheatontheonehandandelectromagnetismandopticsontheother.Mechanicalandheatphe-nomenainvolvethemotionofparticlesasgovemedbyNewton'sequations.Electromagnetismandopticsdealwithfieldsandwaves,whicharedescribedbyMaxwell'sequations.Intheclassicaldescriptionofparticlemotion,thepositionoftheparticleisexactlydeterminedatanygivenmoment.Wavephenomena,incontrast,arecharacterizedbyinterferencepattemswhichex-tendoveracertainregioninspace.Thestrictseparationofparticleandwavephysicslosesitsmeaninginatomicandsubatomicprocesses.QuantummechanicsgoesbacktoMaxPlanck'sdiscoveryin1900thattheenergyofanoscillatoroffrequencyvisquantized.Thatis,theenergyemittedorabsorbedbyanoscillatorcantakeonlythevalues0,hv,Ihv,....OnlymultiplesofPlanck'squantumofenergyarepossible.Planck'sconstantisafundamentalconstantofnature,thecentraloneofquantumphysics.Oftenitispreferabletousetheangularfrequencyw=2voftheoscillatorandtowritePlanck'squantumofenergyintheform1.1ThePhotoelectricEffectThephotoelectriceffectwasdiscoveredbyHeinrichHertzin1887.ItwasstudiedinmoredetailbyWilhelmHallwachsin1888andPhilippLenardin1902.Wediscussherethequantitativeexperiment,whichwasfirstcarriedoutin1916byR.A.Millikan.HisapparatusisshownschematicallyinFigure1.la.Monochromaticlightofvariablefrequencyfallsontoaphotocathodeinavacuumtube.Oppositethephotocathodethereisananode-weassumecathodeandanodetoconsistofthesamemetal-whichisatanegativevoltageUwithrespecttothecathode.Thustheelectricfieldexertsarepellingforceontheelectronsofcharge-ethatleavethecathode.Heree=1.609xl0-19Coulombistheelementarycharge.Iftheelectronsreachtheanode,theyflowbacktothecathodethroughtheextemalcircuit,yieldingameasurablecurrent1.Thekineticenergyoftheelectronscanthereforebedeterminedbyvaryingthevoltagebetweenanodeandcathode.Theexperimentyieldsthefollowingfindings.1.Theelectroncurrentsetsin,independentofthevoltageU,atafrequencyvothatischaracteristicforthematerialofthecathode.Thereisacurrentonlyforv>V0.2.ThevoltageUsatwhichthecurrentstopsflowingdependslinearlyonthefrequencyofthelight(Figurel.lb).