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1、Experiment#7,GeometricalOpticsImageFormationbyaThinLens1PurposeThepropagationoflightthroughopticaldeviceswhosedimensionsarelargecomparedtothewavelengthsofthelightcanbeunderstoodusingraydiagramstodenotethedirectionsofpropagationofthelightthroughtheopticalcomponentsof
2、thedevice,e.g.,lenses,etc.Inthisexperimentwewillstudythepropagationoflightthroughalensandverifythebasiclensequations.2TheoryA.Focusingofparallelbeamsoflightraysbyathinlens.Ifaparallelbeamoflightraysisincidentonathinconvexlens,therayswillbemadetoconvergebyrefractiona
3、tthelenssurfacesandwillbebroughttoafocusinthefocalplaneofthelens.ThisisshowninFigure1forabeamofraysparalleltotheaxisofthelenswhichconvergetoapointontheaxisofthelensinthefocalplane,i.e.,thefocalpointofthelens.Figure1.FocusingofaParallelLightBeam.Thedistanceofthefocal
4、planefromthelens,thefocallengthf,isacharacteristicparameterofanylensandisdirectlyproportionaltotheradiiofcurvatureofthelenssurfaces(sphericallenses).Thus,thefocallengthofalensisinverselyrelatedtothefocusingpowerofthelens,i.e.,ashorterfocallengthlenshasa"stronger"foc
5、usingpower.Sincelightraysarereversible,itfollowsthatifapointsourceoflightisplacedatapointinthefocalplaneofthelens,thelightraysdivergingfromitwillberefractedthroughthelensintoaparallelbeamoflightraysontheotherside(Figure2).Figure2.FocusingofaPointLightSourceintheFoca
6、lPlaneintoaParallelBeam.B.Formationofrealimagesbythin,convexlenses.Ifasmallobjectisplacedatadistanceufromthelens,outsideofthefocalplane(u>f),arealimage(thatcanbeprojectedonascreen)willbeformedinan"imageplane"atadistancevontheothersideofthelens(Figure3).Corresponding
7、toeverypointontheobject,suchasthetipofthearrow(pointP),thereisapointontheimage(P')intheimageplanetowhichalllightraysdivergingfromtheobjectpointwillconvergeafterpassingthroughthelens.ThisisindicatedinFigure3.Figure3.RealImageFormationbyaConvexLens.Theimagepointcorres
8、pondingtoagivenobjectpointcanbelocatedgeometricallybydrawingthreecharacteristicraysdivergingfromtheobjectpointandpassingthroughthelens.The
