15 Waves Alevel考试物理课件

WavestypesofwavesMechanicalwavesRequirematerialsubstanceElectromagneticwavesDon’trequiremediumElectromagneticwavesarecausedbytheinteractionbetweenanelectricalcurrentandamagneticfield.EMRhasboth

electricandmagneticfieldcomponents,whichstandinafixedratioofintensitytoeachother,andwhichoscillateinphaseperpendiculartoeachotherandperpendiculartothedirectionofenergyandwavepropagation.Invacuum,electromagneticradiationpropagatesatacharacteristicspeed,thespeedoflight.mechanicalwaves.rarMechanicalwavesCondition：SourcemediumTransverseandlongitudinalwavesWaveswhichmoveenergyfromplacetoplacearecalledprogressivewaves.Atransversewaveisoneinwhichthevibrationsoftheparticlesinthewaveareatrightanglestothedirectioninwhichtheenergyofthewaveistravelling.Alongitudinalwaveisoneinwhichthedirectionofthevibrationsoftheparticlesinthewaveisalongthedirectioninwhichtheenergyofthewaveistravelling.transversewaves

andlongitudinalwavesoscillatingdirection⊥travellingdirectiontransversewaves

oscillatingdirection∥travellingdirection

longitudinalwavesGraphicalrepresentationofwaves:Thedisplacementofaparticleonawaveisitsdistancefromitsrestposition.Theamplitudeofthewavemotionisdefinedasthemaximumdisplacementofaparticleinthewave.Thelengthofthesmallestrepetitionunitiscalledthewavelength.Onewavelengthisthedistancebetweentwoneighboringpeaks(crest)ortwoneighboringtroughs,ortwoneighboringpointswhicharevibratingtogetherinexactlythesameway(inphase).Itisthedistancemovedbythewaveduringoneoscillationofthesourceofthewaves.Theperiod(T)

ofthewaveisthetimeforaparticleinthewavetocompleteonevibration,oronecycle.Thenumberofcompletevibrations(cycles)perunittimeiscalledthefrequency(f)ofthewave.Phase:thecrestsortroughsoftwowavesofthesamefrequency.Whenthecrestsandtroughsoftwowavesarealigned,thewavesaresaidtobeinphase.Whenacrestisalignedwithatrough,thewaveareoutofphase.Thephasedifferencebetweenwavesthatareexactlyoutofphaseisπradiansor180°.phasedifferenceof90°θyo1-1-

234phasedifferencebetweenwavesThephasedifferencebetweenthesameparticleondifferentwavesis90°yo1-1-

234phasedifferenceof180°θThephasedifferencebetweenthesameparticleondifferentwavesis180°2π(t/T)rad=360(t/T)°.510152025303540t/sdisplacementTheamountofenergypassingthroughunitareaperunittimeiscalledtheintensityofthewave.ForawaveofamplitudeAandfrequencyf,theintensityI

isproportionaltoA2f2.Ifthewavefromapointsourcespreadoutequallyinalldirections,wehavewhatiscalledasphericalwave.I=W/4πr2Waveequation:EgAtuningforkoffrequency170Hzproducessoundwavesofwavelength2.0m.Calculatethespeedofsound.EgTheamplitudeofawaveinaropeis15mm.Iftheamplitudewerechangedto20mm,keepingthefrequencythesame,bywhatfactorwouldthepowercarriedbytheropechange?rippletankpattersforlowandhighvibrationsPropertiesofwavemotions:Wavefront:Ifweconsideraripplespreadingoutonthesurfaceofapondafterapebblehasbeenthrownintothewater,asnapshotoftherippleatsomeinstantcanberepresentedasacircleiscalledawavefront.Forwaterwavesweseethewavefronts;whileforlightweseetherays.Interference:iftwoormorewavesoverlap,theresultantdisplacementisthesumoftheindividualdisplacements.theoverlappingwavesInterferencepatternRippletankpatternforonepointRippletankpatternfortwopointsReflection:theangleofreflectionequalstheangleofincidence,andthereisnochangeinwavelength.Refraction:Thechangeindirectionofawaveduetoachangeinspeediscalledrefraction.Theshallowerthewater,theslowerthespeed.Thus,thewavesmovemoreslowlyastheypassovertheglassblock.Thefrequencyofthewavesremainsconstant,andsothewavelengthdecreases.Diffraction:whenwavespassthroughanarrowgap,theyspreadout.Theextentofdiffractiondependsonthewidthofthegapcomparedwiththewavelength.

Thespreadingofawaveintoregionswhereitwouldnotbeseenifitmovedonlyinstraightlines.

直线水波的衍射动画-视频资源-山不在高——揭晓青物理工作站-江西教师网/ndzxjxq/column30891/4b0adc34-7b84-4c69-ac4e-102cb869c12e.html/kecheng/lxy/lab/pages/jxb9.htmPolarisationofwavesThetransversevibrationsoftheropewillbeinjustoneplane-theverticalplaneifyourhandismovingupanddown,orthehorizontalplaneifitmovesfromsidetoside.Iftheropepassesthroughahorizontalslit,onlywavesgeneratedbyaside-to-sidemotionofthehandwillbetransmitted.Iftheropepassesthroughaslitofoneorientationfollowedbyoneoftheotherorientation,thewaveistotallyblockedwhetheritwasinitiallyintheverticalorthehorizontalplane.Theconditionforawavetobeplane-polarisedisforthevibrationstobeinjustonedirectionnormaltothedirectioninwhichthewaveistravelling.Polarisationcanapplyonlytotransversewaves.Longitudinalwavesvibratealongthedirectionofwavetravel,andwhatevertheorientationoftheslit,itwouldnodifferencetothetransmissionofthewaves.Thesunanddomesticlightbulbsemitunpolarisedlight;thatis,thevibrationstakeplaceinmanydirectionsatonce,insteadofinthesingleplaneassociatedwithplane-polarisedradiation.Unpolari