seeing color with cd’s

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SeeingColorwithCD’s

GradeLevel/sMS,HS Materials:CD’s,flashlights,LED’sofdifferentcolors

Subject:PhysicalScience

Objective:UnderstandthevisiblespectrausingaCDandaCDspectroscope.

AdvancedPreparationofmaterials:

Part1:

Part2:

ExplorethecolorsreflectingofftheCD.Howmanycolorsdoyousee?Describetheshapesofthecolors.WhatothershapesdoyouseereflectedontheCD?

WhatifwechangetheangleatwhichyoulookattheCD?Whatifwechangethelightsource?Exploreusingthedifferenttypesoflightsavailable.EX:LED’s,incandescent,florescent,sunlight

StandardsDisciplinaryCoreIdeas–PS4Crosscuttingconcepts: CauseandEffect Patterns

StructureandFunctionScienceandEngineeringPractices: Askingquestionsanddefiningproblems Planningandcarryingoutinvestigations

Developingandusingmodels

PurchaseorcollectCD’sforeachstudent.Make8CDspectroscopes–linktoinstructionsonlastpage.

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UnderlyingScience:WhydoesaCDsplitlightintoits’differentcolors?ACDismadeupoftwolayersofplasticprotectingathinlayerofaluminumonwhichthemusicordataisstored.Thisinformationisstoredinpitsorganizedincirculartracks.Linesofshinyaluminumwill“reflectwell”nexttolinesofpitswhich“reflectpoorly”.Thespacebetweentheselinesandpitsareveryclosetogether.Infact,theyaresoclosetogetherthattheyactasadiffractiongratingforlight.Thereflectionswillinterferewitheachotherconstructivelyanddestructively.

Whitelightisamixtureofcolors.Whenwelookatdifferentlightsourceswithoureyestheymightappeartobethesameshadeofwhite.UsingtheCDrevealsthattheyarecomposedoftotallydifferentcolorsorspectra.LightreflectedofftheCDisduetodiffraction,buttheamountoflightislarge.Thebestwaytolookatthecolorsorspectraoflightistoreducetheamountoflightlikeapinhole.Wewillinvestigatethespectraoflightusingaspectroscopewithaslit.SpectroscopeActivityHoldthetubeuprightandpointthetopslitatalightsource.Pressyoureyetotheviewinghole.Photoonpage3–viewingwithaspectroscope.OntheCD,lookforaclear,solidlineoflightbrokenupintocolorbands:thisisthespectrumoflightreflectedfromthelightontotheCD.AdjusttheangleatwhichyoulookthroughtheviewingholeattheCDtofindthebestviewofthelightspectrum.Differenttypesoflightsources:Fluorescentlight–producesbrightlinesproducedbythespectrumofthemercurygasinsidethetube.Incandescentlight–bycomparison,makesacontinuousspectrumofthespectrum(rainbow)ofcolors.UnderlyingScienceAlllightismadeupofwavesofelectromagneticradiation.Aspectroscopespreadseachdifferentwavelengthtoadifferentpositionwithinaspectrumoflight.Whenthelightentersthetube,itisspreadintoaspectrumperpendiculartotheCDtracks.Thisiswhytheslitandtheviewingholearelocatedatrightangles.Eachcolorbendsataparticularangle.Foryoutoseethespectrum,thelightmustdiffractofftheCDandreflectintoyoureye.AdjustingthetiltoftheCDallowsyoutoproperlybouncethespectrumintoyoureye.

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Resources:

SafetyConsiderations:NeverusediffractiongratingstolookdirectlyattheSUN!

aapt.org/k12/TPTlessons.cfmOSA–OpticalSocietyCDSpectroscopewww.exploratorium.edu/snacks/cd-spectroscopeGetNakedPhysics–KitchenScienceExperiments–CDScienceFormoreinformationorquestionscontact:

KathyHolt–LIGOScienceEducationCenter

kathy.holt@ligo.org