Wave Motion

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1、WaveMotionDisplacement(y):Positionofanoscillatingparticlefromitsequilibriumposition.Amplitude(y0orA):Themaximummagnitudeofthedisplacementofanoscillatingparticlefromitsequilibriumposition.Period(T):Timetakenforaparticletoundergoonecompletecycleofoscillation.Frequency(f):Numberofoscil

2、lationsperformedbyaparticleperunittime.Wavelength(λ):Foraprogressivewave,itisthedistancebetweenanytwosuccessiveparticlesthatareinphase,e.g.itisthedistancebetween2consecutivecrestsor2troughs.Wavespeed(v):Thespeedatwhichthewaveformtravelsinthedirectionofthepropagationofthewave.Wavefro

3、nt:Alineorsurfacejoiningpointswhichareatthesamestateofoscillation,i.e.inphase,e.g.alinejoiningcresttocrestinawave.Ray:Thepathtakenbythewave.Thisisusedtoindicatethedirectionofwavepropagation.Raysarealwaysatrightanglestothewavefronts(i.e.wavefrontsarealwaysperpendiculartothedirectiono

4、fpropagation). Fromthedefinitionofspeed,Speed=Distance/TimeAwavetravelsadistanceofonewavelength,λ,inatimeintervalofoneperiod,T.Thefrequency,f,ofawaveisequalto1/TTherefore,speed,v=λ/T=(1/T)λ=fλv=fλ4Example1:Awavetravellinginthepositivexdirectionisshowedinthefigure.Findtheamplitude,wa

5、velength,period,andspeedofthewaveifithasafrequencyof8.0Hz.Amplitude(A)=0.15mWavelength(λ)=0.40mPeriod(T)=1f=18.0≈0.125sSpeed(v)=fλ=8.0x0.40=3.20ms-1Awavewhichresultsinanettransferofenergyfromoneplacetoanotherisknownasaprogressivewave.Intensity{ofawave}:isdefinedastherateofenergyflow

6、perunittime{power}perunitcross-sectionalareaperpendiculartothedirectionofwavepropagation.Intensity=Power/Area=Energy/(TimexArea)Forapointsource(whichwouldemitsphericalwavefronts),Intensity=(½mω2xo2)/(tx4πr2)wherex0:amplitude&r:distancefromthepointsource.Therefore,I∝xo2/r2(PtSource)F

7、orallwavesources,I∝(Amplitude)2 Transversewave:Awaveinwhichtheoscillationsofthewaveparticles{NOT:movement}areperpendiculartothedirectionofthepropagationofthewave.4Longitudinalwave:Awaveinwhichtheoscillationsofthewaveparticlesareparalleltothedirectionofthepropagationofthewave. Polari

8、sationissaidtooccur