refraction



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

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