浙江大学大学物理甲下-chapter-43.ppt

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1、Chapter43GratingsandSpectra8/2/2021143-1MultipleSlits8/2/202128/2/202138/2/202141.Thespacingofthefringesisdeterminedbytheslitseparationd,independentlyofthenumberofslits.Thefringesaresharper(narrower),whenthenumberofslitsincreases.2.Thefaintsecondarymaxi

2、maappearbetweenadjacentbrightfringes.Asthenumberofslitsincreases,thenumberofsecondarymaximaincreasesbuttheirbrightnessdecreases.Grating:thenumberofslitsNmaybeaslargeas104percm.8/2/20215Thelocationofprincipalmaximaisdeterminedby:Principalmaximadisslipse

3、paration,alsoiscalledgratingconstant(gratingspacing).8/2/20216SecondarymaximaTherearesomeminimabetweentwoprincipalmaxima.Superpositionofsomephasors8/2/202173slipsThere2minimabetweentwoprincipalmaxima.1231238/2/202184slipsThere3minimabetweentwoprincipal

4、maxima.8/2/20219IfthegratinghasNslips,thereareN-1minimabetweentwoprinciplemaxima.Thereisasecondarymaximumbetweentwominima.IfthegratinghasNslips,thereareN-2secondarymaximabetweentwoprinciplemaxima.Thusthemoretheslipsare,themorethesecondarymaximaare,themo

5、rethintheprinciplemaximumis.8/2/202110N=2N=3N=4N=5N=10Between2principalmaxima:N-1minima,N-2maxima8/2/202111WidthoftheprinciplemaximaForthefirstminimumofzerointensity,thephasedifferencebetweenwavesfromadjacentslitsisForcentralprincipalmaximum,itswidthca

6、nberepresentedby.(Figure43-5)72°N=5N=28/2/202112ThecorrespondingpathdifferencebetweenadjacentslitsisThemaximabecomessharper.8/2/202113Forthewidthofmthprincipalmaximum(figure43-5)Ndisthetotalwidthofthegrating.AsNdisincreasing,theisdecreasing,themaximabec

7、omesharper.8/2/202114Intensitydistribution8/2/202115I/I0I/I0I/I0I/I0single-slitdiffractiondouble-slitinterferencedouble-slitdiffractiongratingdiffraction8/2/202116Missingorderm1thfringeisnotseen,thisismissingprinciplemaxima.I/I05thprinciplemaximumismi

8、ssingbecaused/a=5.And10th,15th,…also.8/2/20211743-2DiffractiongratingsTransmissiongratingReflectiongratingAcompactdiskisadiffractiongrating.8/2/202118*screenVERYfarawayqDiffractionGrating8/2/202119Spectrumoflightcentral1st(m=1)2n