lecture21_handout力和热-伊利诺伊香槟分校.ppt

《lecture21_handout力和热-伊利诺伊香槟分校.ppt》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、Physics101:Lecture21WavesWavesOverviewTypesSpeedTraveling(“harmonic”)SuperpositionStanding05TypesofWavesLongitudinal:ThemediumoscillatesinthesamedirectionasthewaveismovingSoundTransverse:Themediumoscillatesperpendiculartothedirectionthewaveismoving.Water8SlinkyPreflight3Supposethatalongitudina

2、lwavemovesalongaSlinkyataspeedof5m/s.Doesonecoiloftheslinkymovethroughadistanceoffivemetersinonesecond?1.Yes2.No5m12VelocityofWavesAct17Aspringandslinkyareattachedandstretched.Comparethespeedofthewavepulseintheslinkywiththespeedofthewavepulseinthespring.A)vslinky>vspringB)vslinky=vspringC)vsli

3、nky

4、mpleteoscillation.Speed:ThewavemovesonewavelengthinoneperiodTsoitsspeedisv=/T.22f=v/lTravelingWavesExercisey(x,t)=Acos(wt–kx)Labelaxisandticmarksifthegraphshowsasnapshotofthewavey(x,t)=2cos(4t–2x)atx=0.t+2-2p/2p/43p/425Preflight1+2Supposeatravelingwavemovesthroughsomemedium.Iftheperiodofthe

5、waveisincreased,whathappenstothewavelengthofthewaveassumingthespeedofthewaveremainsthesame?1.Thewavelengthincreases2.Thewavelengthremainsthesame3.Thewavelengthdecreases26Thewavelengthofmicrowavesgeneratedbyamicrowaveovenisabout3cm.Atwhatfrequencydothesewavescausethewatermoleculesinyourburritot

6、ovibrate?(a)1GHz(b)10GHz(c)100GHzACT29Recallthatv=lf.HHOACTSolution30Absorptioncoefficientofwaterasafunctionoffrequency.f=10GHzVisible“waterwindow”31InterferenceandSuperpositionWhentwowavesoverlap,theamplitudesadd.Constructive:increasesamplitudeDestructive:decreasesamplitude34ReflectionActA

7、slinkyisconnectedtoawallatoneend.Apulsetravelstotheright,hitsthewallandisreflectedbacktotheleft.ThereflectedwaveisA)InvertedB)Upright37StandingWavesFixedEndpointsFundamentaln=1(2nodes)ln=2L/nfn=v/l=nv/(2L)44StandingWaves:f1=fundamentalf