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1、1IGCSEPhysicsWaves2Lesson5–DiffractionandthewaveequationAims:Torecallandusetherelationshipbetweenthespeed,frequencyandwavelengthofawave:wavespeed=frequency×wavelength,v=f×λTounderstandthatwavescanbediffractedthroughgapsorwhentheypassanedge,andthattheextent

2、ofdiffractiondependsonthewavelengthandthephysicaldimensionofthegap.3TherippletankArippletankisadeviceusedtostudythebehaviourofwaves,becauseallwavesbehaveinasimilarmanner.Arippletankproduceswaterwavesthatcanbereflected,refractedanddiffracted.paddlevibratesto

3、producewaves4ReflectionandrefractionpaddleWhatdoyouthinkwillhappenifabarrierisplacedinfrontofthewaterwaves?Ifitisaplanebarrierthenthewavesarereflected.barrierWhatdoyouthinkwillhappenifablockissubmergedintherippletank?Thechangeindepthofthewatercausesachangei

4、nspeedofthewaves–theyarerefracted.5BarrierwithlargegapWhatwillhappenifthewidthofthegapinthebarrierislargerthanthewavelengthofthewaves?Thewavespassthroughthegapunchangedapartfromslightdiffractionofthewavesneartheirends.7DiffractionthroughabiggapShadowzoneSha

5、dowzoneWeoftenimaginethatwavespassingthroughabiggapwillbehavelikethis.8DiffractionoccursatedgesInrealitythewavescurveslightlywhentheypasstheedgesofthegap.9Barrierwithwavelength-sizedgapWhatwillhappenifthewidthofthegapinthebarrierissimilarinwidthtothewavelen

6、gthofthewaves?Circularwavesareproduced.Thiseffectisknownasdiffraction.DiffractionDiffractionisthebendingofwavesastheypassthroughagaporpastanedgeWhenawave(front)isIncidentonanedgeoranobstacle/slit/gapWave‘bends’intothegeometricalshadow/changesdirection/sprea

7、dsDiffractioneffectsaremostobviouswhentheobjectoraperturecausingthediffractionissimilarinsizetothewavelengthofthewaves.Lessoccursifwavelengthissmallerthantheobject.Moreoccursifwavelengthislargerthantheobject.Thenearertheslitsizeistothewavelength,themorethew

8、avewilldiffract.1.Thesmallerthegapthegreaterthediffraction.2.Thelongerthewavelengththegreaterthediffractiondiffractionofplanewaves16Whenawaterwavehitsanobstacle,thewavesspreadoutroundtheedgeandbecomesc