Basicdefinition
Whenlightentersanothertransparentmedium(suchaswater)obliquelyfromatransparentmedium(suchasair),thepropagationdirectiongenerallychanges.Thisphenomenoniscalledopticalrefraction.Alsoknownasrefraction,itisanopticaltermthatreferstothephenomenonthatthedirectionoflightischangedduetothedifferenceinwavespeedwhenlightentersanothermediumfromonemedium,orwhenitmovesinpartsofthesamemediumwithdifferentrefractiveindices.Forexample,whenawoodenstickisinsertedintothewater,itwillbethoughtthatthewoodenstickbendswhenitentersthewaterwiththenakedeye.Thisistheresultofrefractionwhenlightentersthewater.
Physicalmeaning
Phenomenon
Thefishswimmingintheclearwatercanbeseenclearly.However,gotoforkitinthedirectionyouseethefish,butyoucan't.Experiencedfishermenknowthatonlybyaimingatthebottomofthefishcantheharpoonbereached.
Lookingatobjectsintransparentmediasuchaswaterandglassfromabove,youwillfeelthatthepositionoftheobjectishigherthantheactualposition.Thisiscausedbythephenomenonoflightrefraction.
Duetotherefractionoflight,thepoolwaterlooksshallowerthanitactuallyis.Therefore,whenyoustandontheshoreandseethecrystalclearwaterthatisnomorethanwaist-deep,don'tgodownrashly,lestyougetpanickedanddangerousbecauseyouunderestimatethedepthofthewater.
Putapieceofthickglassinfrontofthepen,andthebarrelofthepenlooks"displaced".Thisphenomenonisalsocausedbytherefractionoflight.
Law
Thelawofrefractionoflight:whenlightenterswaterorothermediaobliquelyfromtheair,therefractedlightandtheincidentlightandnormalareonthesameplane,andtherefractedlightandtheincidentlightareseparatedOnbothsidesofthenormalline;theangleofrefractionissmallerthantheangleofincidence;whentheangleofincidenceincreases,theangleofrefractionalsoincreases;whenthelighthitsthesurfaceofthemediumperpendicularly,thepropagationdirectionremainsthesame,andthelightpathisreversibleduringrefraction.Whenlightentersairobliquelyfromwaterorothermedia,theangleofrefractionisgreaterthantheangleofincidence.
Understanding
Thelawofrefractionisdividedintothreepoints:(1)Threelinesandonesurface(2)Twolinesareseparated(3)Therelationshipbetweentwoanglesisdividedintothreecases:①Whentheincidentlightisincidentperpendiculartotheinterface,Theangleofrefractionisequaltotheangleofincidenceequalto0°;②Whenthelightisobliquelyshotfromtheairintowaterandothermedia,theangleofrefractionislessthantheangleofincidence;③Whenthelightisobliquelyshotintotheairfromamediumsuchaswater,theangleofrefractionisgreaterthantheangleofincidence(butexistsintheair)Theangleisalwaysabigangle).
Intherefractionoflight,thelightpathisreversible.
RefractiveIndex
Englishname:indexofrefraction;refractiveindex
Definition:Whenlightentersthemediumfromavacuumandisrefracted,Whenthelightisrefracted,theincidentangleandtherefractionangleconformtoSnell'sLaw(Snell'sLaw).Therationofthesineoftheincidentangleitotherefractionangleriscalledthe"absoluterefractiveindex"ofthemedium,or"refractiveindex"forshort.
Formula:n=sini/sinr,thisformulaiscalledtheSnellformula.
Explanation:Thephysicalquantitythatrepresentstheratioofthespeedoflightinthetwomedia.Whenlightpenetratesfromtheairintoacompactmedium(solid,wateroranyliquid),itchangesitsdirection.Theratioofthesineoftheincidentangleofthelighttothesineoftherefractionangle,ortheratioofthespeedofthelightwhenitpassesthroughavacuumtowhenitpassesthroughthemedium,istherefractiveindex.Therefractiveindexvarieswiththenatureanddensityofthemedium,thewavelengthofthelight,andthetemperature.Therefractiveindexofthemediumisgenerallygreaterthan1.Thesamemediumhasdifferentrefractiveindexesfordifferentwavelengthsoflight.Therefractiveindexofvisiblelightusuallyincreasesasthewavelengthdecreases,thatis,redlightisthesmallestandpurplelightisthelargest.Unlessotherwisespecified,therefractiveindexvalueofanobjectreferstosodiumyellowlight(Dline).Therefractiveindexismeasuredinarefractometeratacertaintemperature(usually20°C).Insomecases,themeasurementofrefractiveindexcanbeusedtoobservetheprogressofthepolymerizationreaction.Inthepaintindustry,thedifferencebetweentherefractiveindexofthemediumandthepigmentcanbeusedtodeterminethehidingpowerofthepaint.Intheplasticsindustry,therelationshipbetweenrefractiveindexandtemperaturecanbeusedtodeterminethesolidificationtemperatureoftransparentresins.Intheoilandsesameoilindustry,therefractiveindexisanimportantphysicalconstantincrystals,etc.
Totalreflection
Thelightistransmittedfromthelightdense(thatis,themediuminwhichthelighttravelsatalowspeed)totheinterfaceofthelight(thatis,thelighttravelsatahighspeedinit)mediumWhen,allarereflectedbackintotheoriginalmedium.
Whenlighthitstheinterfaceoftwomedia,onlyreflectionoccurswithoutrefraction.Whenthelightisemittedfromtheopticallydensemediumtotheopticallysparsemedium,therefractionanglewillbegreaterthantheincidentangle.Whentheincidentangleincreasestoacertainvalue,therefractionanglewillreach90°.Atthistime,therewillbenorefractedlightintheopticallythinmedium.Aslongastheincidentangleisgreaterthantheabovevalue,therewillbenorefractionphenomenon,whichistotalreflection..Therefore,theconditionsfortotalreflectionare:(1)Thelightmustbeemittedfromtheopticallydensemediumtotheopticallythinmedium.②Theincidentanglemustbegreaterthanthecriticalangle.
Thecriticalangleistheangleofincidencewhentherefractionangleis90degrees(totalreflectionwillonlyoccurwhenthelightenterstheopticallydensemediumandtheincidentangleisgreaterthanthecriticalangle)
Relativerefraction
DiscoveredbytheDutchmathematicianSnell,itisthelawthatdeterminesthedirectionofrefractedlightinthephenomenonoflightrefraction.Whenlightentersthesecondmedium(refractiveindexn2)fromthefirstmedium(refractiveindexn1),partofthelightisrefractedafterenteringthesecondmediumfromthefirstmediumonthesmoothinterface.
Theexperimentpointedout:(1)Therefractedraysarelocatedintheplanedeterminedbytheincidentrayandtheinterfacenormal;(2)Therefractedraysandtheincidentraysareonbothsidesofthenormal;(3)TheincidentangleiTheratioofthesineofthesinetothesineoftherefractionanglei′isaconstantforthetwomediawithacertainrefractiveindex.
Insimpleterms,lightentersthemediumwithahighspeedoflightintoamediumwithalowspeedoflight.Wheninthemiddle,theangleofrefractionissmallerthantheangleofincidence;whenenteringfromamediumwithalowspeedoflightintoamediumwithahighspeedoflight,theangleofrefractionisgreaterthantheangleofincidence.
Thislawisthebasicexperimentallawofgeometricoptics.Itissuitableforhomogeneousandisotropicmedia.Forvariousopticalinstrumentsusedtocontroltheopticalpathandforimaging,theprincipleoftheopticalpathstructureismainlybasedonthelawoflightrefractionandreflection.Thislawcanalsobederivedfromtheconceptoflightfluctuations,soitcanalsobeappliedtorefractionphenomenasuchasradiowavesandsoundwaves.
Thelawofrefraction(lawofrefraction)orSnell'slaw(Snell'sLaw)
LightrefractsthroughtheinterfaceoftwomediaAtthetime,thelawthatdeterminestherelationshipbetweentheincidentlightandthepropagationdirectionoftherefractedlightisoneofthebasiclawsofgeometricoptics.Theplaneformedbytheincidentlightandthenormallineoftheinterfacepassingthroughtheincidentpointiscalledtheincidentsurface.Theanglebetweentheincidentlightandtherefractedlightandthenormaliscalledtheangleofincidenceandtheangleofrefraction,andisrepresentedbyθiandθt.Thelawofrefractionis:①Therefractedlightisintheincidentplane.②Theratioofthesineoftheincidentangleandtherefractionangleisaconstant,representedbyn21,thatis
sinθi/sinθt=n21
sinθi/sinθt=v1/v2=n21
wheren21iscalledtherelativerefractiveindexofthesecondmediumtothefirstmedium.
ThefirsttoquantitativelystudythephenomenonofrefractionwastheGreekC.Ptolemyinthe2ndcenturyAD.Hemeasuredthecorrespondencebetweentheangleofincidenceandtheangleofrefractionwhenlightisrefractedfromairtowater,althoughtheexperimentalresultsarenotaccurate.,Buthewasthefirstpersontoquantitativelystudythelawofrefractionthroughexperiments.In1621,DutchmathematicianW.Snellaccuratelydeterminedthroughexperimentsthelawthattheratioofthecosecantoftheincidentangletotherefractionangleisaconstant,thatis,
cscθi/cscθt=constant
SothelawofrefractionisalsocalledSnell'slaw.In1637,theFrenchmanR.DescartesfirstannouncedthelawoftheratioofsinesinmodernforminhisbookRefractiveOptics.Likethelawofreflectionoflight,thelawofrefractioninitiallydeterminedbyexperimentcanbeprovedbasedonFermat'sprinciple,Huygens'principleortheelectromagnetictheoryoflight.
Theabove-mentionedlawoflightrefractiononlyappliestoastaticinterfacecomposedofanisotropicmedium.
Relatedapplications
Peopleusetheprincipleofrefractiontoinventlenses.Thereareconvexlensesandconcavelenses,andtherearesixtypesofsubdivisions:double-convex,plano-convex,concave-convex,double-concave,plano-concave,andconvex-concave..
Thecenterpartisthickerthantheedgepartiscalledaconvexlens,andthecenterpartisthinnerthantheedgepartiscalledaconcavelens.Theconvexlenshasthefunctionofconverginglight,soitisalsocalled"converginglens"and"positivelens"Andreadingglasses),theconcavelenshasthefunctionofdiverginglight,soitisalsocalled"divergentlens"and"negativelens"(whichcanbeusedformyopiaglasses).
Lensisthemostbasicopticalelementthatcomposesthemicroscopeopticalsystem.Theobjectivelens,eyepieceandcondenserareallcomposedofsingleandmultiplelenses.
Forexample,magnifyingglass,telescope,microscope,etc.
Peoplealsoappliedtheprincipleoftotalreflectionoflighttomoderncommunicationsandinventedopticalfiber.
Whattheopticalfiberuploadsisnotanelectricalsignal,butanopticalsignal,sothatthesignaltransmissiondistanceismuchlongerthanthatonthecable,whichsavescostsandexpandsthebandwidth.
Thefiberisdividedintotwolayers,theinnerlayerandtheouterlayerhavedifferentdensities,creatingconditionsfortheformationoftotalreflection;inthisway,whenlightisincidentatacertainangle,accordingtotheprincipleoftotalreflection,totalreflectioncanoccur,so,Theenergyconsumedbythelighttravelingintheopticalfiberisverysmall,sotheopticalsignalneedstousearepeatertostrengthentheintensityafteralongdistanceintheopticalfiber.
Introductiontothelens
Lensandclassification
Lens:madeoftransparentmaterial(usuallyglass),atleastonesurfaceispartofasphericalsurface,andthethicknessofthelensItismuchsmallerthanitssphericalradius.
Classification:Convexlens:thinedge,thickcenterConcavelens:thickedge,thincenter
Mainopticalaxis,opticalcenter,focus,focallength
Mainopticalaxis:Astraightlinepassingthroughthecentersofthetwospheres
Opticalcenter:Thereisaspecialpointonthemainopticalaxis,andthedirectionoflightpassingthroughitdoesnotchange.(Thecenterofthelenscanberegardedastheopticalcenter)
Focus:Convexlenscanmakelightparalleltothemainaxisconvergeatapointonthemainopticalaxis.Thispointiscalledthefocalpointofthelensandisrepresentedby"F"
Virtualfocus:Thelightparalleltothemainopticalaxisbecomesdivergentafterpassingthroughtheconcavelens.Thereverseextensionlineofthedivergentlightintersectsatapointonthemainopticalaxis.Thispointisnottheconvergencepointoftheactuallight,soitiscalledthevirtualfocus.
Focallength:Thedistancefromthefocalpointtotheopticalcenteriscalledthefocallength,whichisrepresentedby"f".
Eachlenshastwofocalpoints,focallengthsandanopticalcenter.
Theeffectofthelensonlight
Convexlens:Convergenceoflight(pictured)
Concavelens:Divergenceoflight(pictured)ConvexlensimagingRegular
Objectdistance(u) | Imagedistance(v) | Imagesize | Thevirtualrealityoftheimage | Thepositionoftheimage | Application |
u>2f | f<v<2f | Zoomout | Realimage | Bothsidesofthelens | Camera |
u=2f | v=2f | Samesize | Realimage | Bothsidesofthelens | None |
f<u<2f | v>2f | Zoomin | Realimage | Bothsidesofthelens | Slideprojector |
u=f | Noimaging | ||||
u<f | v>u | Magnification | Virtualimage | Lensonthesameside | Magnifyingglass |
Convexlensimaginglaw:thevirtualimageisonthesamesideoftheobject;therealimageisonthedifferentside;therealimageofthefarobjectissmallandthenearobjectislargeandtherealimageisfaraway.
Inordertomaketheimageonthescreen"upright"(faceup),theslideshouldbeinsertedbackwards.Thecameralensisequivalenttoaconvexlens,andthefilminthedarkboxisequivalenttoalightscreen.Weadjustthefocusring,notthefocus,butthedistancefromthelenstothefilm.Thefarthertheobjectisfromthelens,thefilmshouldbeclosertothelens.
Therefractiveindexofthemediumtolight:[absoluterefractiveindex]
n=sini/sinr
Itmeanswhenlightpropagatesinthemedium,Acharacteristicofthemediumtolight.
Therefractiveindexofthemediumtothemedium:[Relativerefractiveindex]
LightfromthemediumWhen1entersthemedium2,theration21ofthesineoftheincidentangleθ1totherefractionangleθ2iscalledtherefractiveindexofthemedium2relativetothemedium1,thatis,the"relativerefractiveindex".Therefore,the"absoluterefractiveindex"canberegardedastherefractiveindexofthemediumrelativetovacuum.
n'=sinθ1/sinθ2=n2/n1
Itisaphysicalquantitythatrepresentstheratioofthespeedoflightintwo(isotropic)media.
Refractionquestiontype
1.Inthefollowingexamples,thephenomenonoflightreflectionis()
A.SeeingthereflectionofthetreebythecalmlakeB.Therearemanysmallroundspotsunderthedenseshadeoftreesduringtheday.
C.Atnight,Iseemyshadowunderthestreetlamp.D.Thegoldfishintheroundglasstanklooksbigger
2.Atpresent,lightpollutionisbecomingmoreandmoreserious.Whitepollutionisacommontypeoflightpollution.Theglasscurtainwalls,glazedbrickwalls,polishedmarblesandvariouspaintsofbuildingscancausewhitepollution.Themainreasonfortheformationofwhitepollutionis()A,LightreflectionB,lightrefractionC,lighthasenergyD,lightpropagatesalongastraightline
3.Peoplestandinginfrontofanuprightflatmirror,toseetheirfull-lengthimage,thelengthofthemirrorshouldbeatleasttheheightoftheperson()
A,1/3B,1/2C,1/4D,Thesameheight
4.Inordertoallowsunlightatanangleof50°tothehorizontaltoenterthewellvertically,thereflectingsurfaceoftheplanemirrorandthehorizontalplaneshouldbeplacedatanangleof_____degrees.
5.Thereisaliquidlevelslightchangemonitor.Thebasicstructureprincipleisshowninthefigure.Thebeamtransmitteralwaysemitsabeamoflighttotheliquidsurfacebeingmonitoredatacertainangle:thebeamisreflectedbytheliquidsurface,andthereflectedlightishorizontallyplacedontheplane.Thephotoelectricconversionreceiverreceivesitanddisplaysitonthedisplay.IfthelightspotreflectedtothephotoelectricconversionreceivermovesfromS1toS2(S2,S1,S3fromlefttorightinthefigure),itindicatesthattheliquidlevelbeingmonitoredis_____,ifthelightspotreceivedonthereceiverMovingfromS2toS3,itindicatestheliquidlevelbeingmonitored(optional"rising"or"falling").
6.Theexperimentalsituationofstudyingtheimagingcharacteristicsoftheflatmirrorisshowninthefigure.Thecandleflameintheflatmirrorislike_____image(real/virtual),andthefinger_____placedonthe"candleflame"isburned(will/willnot).
7.Asshowninthefigure,theTVremotecanalsoberemotelycontrolledwhenfacingtheceiling.Inthefigure,thelight(infrared)emittedfrompointAisreflectedbytheceilingMNandthenincidentontheTVsetB.Trytodrawadiagramofitsopticalpath.
8.Asshowninthepictureisareflectivestreetlamp,Sisthepositionofthebulb,andthetwooutermostlightraysemittedbythemountainbulbhavebeendrawninthepicture.MNisaflatmirrorwithadjustabletilt.PleasedrawtherangeoflightStoilluminatetheroadinthepicture(reservethenecessaryauxiliarylinesfordrawing).Pleasesuggestawaytoincreasetherangeofthelight:______.
Answer:
1.A2,A3,B4,70
5.Up,down
6.Virtual,no
7.PayattentiontomakingtheimageofAorB
8.PayattentiontotheimageofS