浙江大学大学物理甲下-chapter-41.ppt

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1、ContentofthisChapterTwo-sourceinterferenceDouble-slitinterferenceCoherenceIntensityindouble-slitinterferenceInterferencefromthinfilmMichelson’sinterferometerChapter41Interference9/2/20211Geometricalopticsvs.WaveopticsGeometricaloptics:Thelighttravelinstraightlinepathsorr

2、ays.a/λ>>1Waveoptics(physicaloptics):interference;diffraction.a~λ9/2/2021241-1Two-sourceinterferencet+1-1t+1-1t+2-2+InPhaseConstructiveInterference9/2/20213t+1-1t+1-1t+2-2+DestructiveInterferenceOutofPhase180degrees9/2/20214+Differentf9/2/20215InterferenceRequirementsNee

3、dtwo(ormore)wavesMusthavesamefrequencyandsamepolarizingdirectionMustbecoherent(i.e.wavesmusthavedefinitephaserelation)Interference:Whenidenticalwavesfromtwosourcesoverlapatapointinspace,thecombinedwaveintensityatthatpointcanbegreaterorlessthantheintensityofeitherofthetwo

4、waves.9/2/20216Can’tproducecoherentlightfromseparatesources.(f1014Hz)SinglesourceTwodifferentpathsInterferencepossiblehereNeedtwowavesfromsinglesourcetakingtwodifferentpathsOnesource,twoslitsReflection(thinfilms)Diffraction*9/2/20217SuperpositionofTwoWavesTwowavesencoun

5、teredatpointP:Herewehaveassumptions:(1)Samefrequencies,(2)Amplitudeinsamedirection,and(3)initialphasesarenotchangewithtime.9/2/20218Δr:pathdifference.therelationofphasedifferenceandpathdifference.Theresultamplitudedependson9/2/202199/2/202110OpticalPathLengthTheopticalpa

6、thlengthinamedium:Therefore,differenceoftheopticalpathlengths:BLAn9/2/20211141-2Double-SlitInterference*SinglesourceofmonochromaticlightdD9/2/202112NeedD>>d,λ

7、/2/202114Young’sdouble-slitexperiment(1801)9/2/202115Quickquiz-1IntheYoungdoubleslitexperiment,isitpossibletoseeinterferencemaximawhenthedistancebetweenslitsissmallerthanthewavelengthoflight?(1)Yes(2)NoNeed:dsinq=ml=>sinq=ml/dIfl>dthenl/d>1sosinq>1Notpossible!9/2/202116

8、Quickquiz-2Whichofthefollowingwillcausethefringesinatwo-slipinterferencepatterntomovefartherapart?(1)De