天文学英文版PPT资料 (7)

UniverseEighthEditionRogerA.Freedman•WilliamJ.KaufmannIIICHAPTER5TheNatureofLightReading:AsneededforExam1review(Exam1is9/22)Exam1Material:Chapters1-5Homework:Chapter4QuizdueFriday9/17@9PMChapter5QuizdueTuesday9/21@9PMExam1Review:Iwillpostastudysheetforyourreviewovertheweekend,andIplantodevoteapproximatelyhalfofMonday’slecture9/20toaninformalreviewandQ&Asession.COMEPREPAREDWITHQUESTIONS!5-1Howwemeasurethespeedoflight5-2Howweknowthatlightisanelectromagneticwave5-3Howanobject’stemperatureisrelatedtotheradiationitemits5-4Therelationshipbetweenanobject’stemperatureandtheamountofenergyitemits5-5Theevidencethatlighthasbothparticleandwaveaspects5-6Howastronomerscandetectanobject’schemicalcompositionbystudyingthelightitemits5-7Thequantumrulesthatgovernthestructureofanatom5-8Therelationshipbetweenatomicstructureandthelightemittedbyobjects5-9Howanobject’smotionaffectsthelightwereceivefromthatobjectByreadingthischapter,youwilllearnHowlongdoesittakelighttotravel3×108m?A.1yearB.8minutesC.1minuteD.1secondE.1millisecondQ5.1Howlongdoesittakelighttotravel3×108m?A.1yearB.8minutesC.1minuteD.1secondE.1millisecondA5.1Whichofthefollowingindicatesthatlightbehavesasawave?A.Alternatingbrightanddarkbandsappearonascreenwhenlightofasinglecolorpassesthroughtwoslitsthataresidebyside.B.Lighttravelsat3×108m/s.C.Lightbouncesoffmirrors.D.Lightconsistsofphotons.E.LightcantraveltoEarthfromthemostdistantpartsoftheuniverse.Q5.2Whichofthefollowingindicatesthatlightbehavesasawave?A.Alternatingbrightanddarkbandsappearonascreenwhenlightofasinglecolorpassesthroughtwoslitsthataresidebyside.B.Lighttravelsat3×108m/s.C.Lightbouncesoffmirrors.D.Lightconsistsofphotons.E.LightcantraveltoEarthfromthemostdistantpartsoftheuniverse.A5.2Lighthasaparticlenature,andtheseparticlesarecalledphotons.Whichregionoftheelectromagneticspectrumhasthehighestenergyphotons?A.gammarayB.X-rayC.ultravioletD.visibleE.infraredQ5.7Lighthasaparticlenature,andtheseparticlesarecalledphotons.Whichregionoftheelectromagneticspectrumhasthehighestenergyphotons?A.gammarayB.X-rayC.ultravioletD.visibleE.infraredA5.7Isolatedatoms,suchasatomsinalow-densitygascloud,onlyemitlightatcertainwavelengths.Why?A.Theycannotbemadehotenoughtoemitatallwavelengths.B.Theelectronsintheatomareallowedtohaveanyenergy.C.Theelectronsintheatomareallowedtohaveonlycertainenergies.D.Thereisanucleus,whichmodifiesthepropertiesofthelightafteritisemitted.E.Theatomsareisolatedfromoneanother.Q5.9Isolatedatoms,suchasatomsinalow-densitygascloud,onlyemitlightatcertainwavelengths.Why?A.Theycannotbemadehotenoughtoemitatallwavelengths.B.Theelectronsintheatomareallowedtohaveanyenergy.C.Theelectronsintheatomareallowedtohaveonlycertainenergies.D.Thereisanucleus,whichmodifiesthepropertiesofthelightafteritisemitted.E.Theatomsareisolatedfromoneanother.A5.9DiscussionQuestion44.KeyIdeasTheNatureofLight:Lightiselectromagneticradiation.Ithaswavelikepropertiesdescribedbyitswavelengthandfrequency,andtravelsthroughemptyspaceattheconstantspeedc=3.0108m/s=3.0105km/s.BlackbodyRadiation:Ablackbodyisahypotheticalobjectthatisaperfectabsorberofelectromagneticradiationatallwavelengths.Starscloselyapproximatethebehaviorofblackbodies,asdootherhot,denseobjects.KeyIdeasTheintensitiesofradiationemittedatvariouswavelengthsbyablackbodyatagiventemperatureareshownbyablackbodycurve.Wien’slawstatesthatthedominantwavelengthatwhichablackbodyemitselectromagneticradiationisinverselyproportionaltotheKelvintemperatureoftheobject:max(inmeters)=(0.0029Km)/T.TheStefan-BoltzmannlawstatesthatablackbodyradiateselectromagneticwaveswithatotalenergyfluxFdirectlyproportionaltothefourthpoweroftheKelvintemperatureToftheobject:F=T4.KeyIdeasPhotons:Anexplanationofblackbodycurvesledtothediscoverythatlighthasparticle-likeproperties.Theparticlesoflightarecalledphotons.Planck’slawrelatestheenergyEofaphotontoitsfrequencyorwavelength:E=h=hc/,wherehisPlanck’sconstant.KeyIdeasKirchhoff’sLaws:Kirchhoff’sthreelawsofspectralanalysisdescribeconditionsunderwhichdifferentkindsofspectraareproduced.Ahot,denseobjectsuchasablackbodyemitsacontinuousspectrumcoveringallwavelengths.Ahot,transparentgasproducesaspectrumthatcontainsbright(emission)lines.Acool,transparentgasinfrontofalightsourcethatitselfhasacontinuousspectrumproducesdark(absorption)linesinthecontinuousspectrum.KeyIdeasAtomicStructure:Anatomhasasmalldensenucleuscomposedofprotonsandneutrons.Thenucleusissurroundedbyelectronsthatoccupyonlycertainorbitsorenergylevels.Whenanelectronjumpsfromoneenergyleveltoanother,itemitsorabsorbsaphotonofappropriateenergy(andhenceofaspecificwavelength).Thespectrallinesofaparticularelementcorrespondtothevariouselectrontransitionsbetweenenergylevelsinatomsofthatelement.Bohr’smodeloftheatomcorrectlypredictsthewavelengthsofhydrogen’sspectrallines.KeyIdeasTheDopplerShift:TheDopplershiftenablesustodeterminetheradialvelocityofalightsourcefromthedisplacementofitsspectrallines.Thespectrallinesofanapproachinglightsourceareshiftedtowardshortwavelengths(ablueshift);thespectrallinesofarecedingligh