光的英文課件Wheredoeslightcomefrom?Ourmajorlightsource:theSunWhereelsedoeslightcomefrom?SortinglightsourcesNaturalvs.Man-made(artificial)Aretheselightsources?moonwatermirrorTheseitemsarenotlightsources,insteadtheyarereflectinglightfromothersources.Howdoeslighttravel?Lightraystravelinstraightlinesfromthelightsource.Whenithitsanopaqueobject,somelightisabsorbedandtherestreflectsoff.Iftheobjectistransparent,lightrayspassthroughiteasily.Iftheobjectistranslucent,somelightcanpassthrough,buttherestofthelightwillbereflected.lightsourceHowdowesee?Lightcomingfrom,(orreflectingoff)objectsenterstheeyethroughthecorneathenthepupil.Itisfocusedclearlybythelensontotheretina.Thelightsensitivecellsoftheretinagatherinformationaboutpatternsoflightanddark,colourandmovementandsenditthroughtheopticnerve.Howdowesee?Informationenteringthebrainthroughtheopticnerve,isthentransmittedthroughmorenervepathwaystothevisualcortex.Herethepatternsoflightanddark,colourandmovementareinterpreted.Thebrain,basedonpastexperience,canthenunderstandwhatit‘sees’.Howdoweseecolour?lightsourceLightfrommostlightsourceslookswhite,butactuallycontainsallthecoloursofthespectrum;alsoknownastherainbow.Ifanobjectlooksblue,itisabsorbingeverycolourexceptblue,whichisreflectingoffitandenteringyoureyes.Ifanobjectlooksorange,itisabsorbingeverycolourexceptorange,which,again,isreflectingoffandenteringyoureyes.Ifanobjectlooksred...(Yougettheidea!)Howdoeslightreflect?AngleofincidenceAngleofreflectionThe‘angleofreflection’isalwaysequaltothe‘angelofincidence’.onoffLightcanonlybereflectedinstraightlines.onoffHowdoeslightformshadows?Lightraystravelinstraightlines,radiatingoutfromthelightsource.Ifraysareblockedbyanopaqueobjectashadowformswherethelightcannotreach.Ifthelightsourceismovedclosertotheobject,morelightisblockedandalargershadowisformed.lightsourcelightsourceHowdoessunlightcauseshadows?6am8am9am12am2pm10am3pm4pm7pmLookingNorth,theSunappearstoriseintheEast......andtravelacrosstheskyuntilitsetsintheWest.ThepositionoftheSuneffectsthepositionandlengthoftheshadowscreated.Thankstothisnaturalphenomenonasundialisabletotellusthetime,aslongasitisasunnyday!Nowexplaintoyourpartner:WhatisthedifferencebetweenlightfromtheSunandlightfromthemoon?WhydoestheSunriseintheEastandseti