等離子體振盪和質子的解釋。 (plasma oscillations and ...

Plasmas Oscillations and plasmons explained ... 中文 A2 初級. 宿醉》--評論 ... PlasmasOscillationsandplasmonsexplainedSomynameisKarlBerggren.I'mgonnatalktodayaboutPlasmaOscillationsandPlasmons,andIwanttostartoutbyjustgivingsomephysicalinsightintowhat'sgoingonwiththissystemsandthenI'mgonnadoalittlebitofbackoftheenvelopealgebratoderivetheplasmafrequency.Derivemightbetoostrongatermbecausereally,ifyouwantaproperderivation,you'regonnahavetogotoanothersource,you'regonnahavetolookintoatextbookoranotheronlineresource.Butplasmasareveryinterestingthesedaysandplasmaoscillationsareinterestingbecausethisparticulartypeofsurfaceplasmahasrecentlygotalotofattentionintermsofmakingnanoopticaldevicesandso,that'soneofthereasonspeoplearemoreinterestedinthisarea.So,what'saplasmafirstofall?Well,we'remostlygonnatalkaboutmetalsandmetalsasatypeofplasmaasagasofchargedparticles.Andametalandmetallicplasma,it'saneutralplasmasothatontheaveragethere'sthesamenumberofpositiveandnegativechargesnotlikeI’vedrawnit.Inametal,youhavepositivechargesorscreenednucleithathavethecoreelectronstostillboundthem,andthenthenegativechargesarefreeelectronsthatmovearound.Andifyouthinkaboutwhathappensinsuchaneutralsystemisyoucanrealizethatevenontheaverageit'sgonnabeneutralmaybeoversomeshort-lengthscales.Soifwejustdrawaboxinhere,youmayhavealittlebitextranegativechargeandalittlebitextrapositivecharge,sothattherewillbeoccasionallysomechargeseparations.Solet'sdrawsomechargeseparationhappeninghere.Andthechargeseparationgetsatreallywhatgoesonintheplasma,intheplasmaoscillation,becauseonceyouhaveachargeseparationyouhaveaCoulombforce.Nowintheplasmon,thepositivechargesbecausetheirnucleiarequitestationary,theelectronsmovesointhissytemtheforceisgoingtoacttopullthenegativechargetowardsthepositivejustbecauseelectronsaresomuchlighter,somuchmoremobile.Andasitmoves,it'sgonnapickupkineticenergy.Infact,whenitpassesthepositivecharge,it'sactuallygonnahavethemaximumkineticenergyandthenit'sgonnastartslowingdownbecausetheCoulombforcesisnowgonnabeoppositeinsideandsoitwilljustcomeouthere,turnaroundeventuallycomebackandthereyougettheoscillation.Okayitcomesbackandgoesthrough.Nowtheoscillation,youcanthinkofoscillationsintermsofexchangeofenergy.Sotheexchangeofenergyhereisbetweenanelectro-staticenergyandakineticenergy.Soactually,theexchangehappenstwiceperoscillationperiod.Soyoustartoutwithelectro-staticpotential,youthentransferthekineticpotential,thenbacktoelectro-staticpotentialandthenbacktokinetic,andthenyoucompletethecycle.Backtoelectro-static,soyougothroughtwoexchangesofenergyinasingleperiod.Sothat'sthebasicphysicalpictureofchargeseparationfollowedbyoscillation,andofcoursethatoscillationisnotgonnalastforever.Therewillbealittlebitofdecayorloss,andsotherewillbealittlebitofslowingdownanditwilldampouteventually.Now,inamoremathematicalsense,youcanlookatthestoredpotentialenergyintheelectro-staticsystem.Buttodothat,firstyouneedtomakeaguessattheamountofchargeandtheseparationofthecharges.Andso,we'lljustguesstheelectronchargebecausethesearefreeelectronsthataremoving.Andtheseparation,theonethat'sthemostlogicalisjusttheaverageseparationofparticlesinthesystemwecall"S"andthatwillbethecuberootoftheinversedensity,ortheparticledensity.So,ifyourememberalittlebitofyourelectricityandmagnetism,thepotentialenergystoredbetweentwoseparatedchargesisgoingtobejustcoulomb’sconstant,timesthechargesquared,overtheseparation.AndifyourememberyourharmonicoscillatorPhysics,sothisisfromclassicalmechanics.Andbytheway,I'massumingthatyourememberelectrostaticsandclassicalmechanicsifyoustudiedthose.Ifyouhaven't,youneedtocatchuponthatareatounderstandthis.Butinthatcase,theharmonicoscillatorenergyisone-halfandwecallthatOmega-P,that'sgonnabetheoscillationfrequency,andXsquared,sothat'sthestandardformforthekinetic,fortheenergystoredintheoscillator.NotanX,thatshouldactuallybeanS,S-squared.So,seenthisasequalasalittlebitoddbecauseit'sclearlynotatrulyharmonicoscillatorbecausetheforceactingonthisgoeslikeoneovertheseparationsquaredandit'snotproportionaltotheseparationasitshouldbeinaharmonicoscillator,sothat'swherethisderivationisreallyquiterough.Butitgivesyouthecorrectform,anditgivesyouthecorrectphysicalinsight.Andtheresultsofalittlebitofalgebraisjustthattheplasmafrequencyscaleswiththesquare-rootofthefreecarrierdensitysquared,chargesquared,anddividedbythemass.Andthisisactuallytheeffectofmass,nottheelectronmass.Butatthispoint,we'veignoredallsortsofotherfactorssolikeColomb’sconstanthasdisappeared.AndsoinfactI'mgonnareplacethatequalitywithjustalittleproportionaltosymbol.Soittellsyouthattheplasmafrequencywhichistypicallyintheultra-violetformetals,itgoesupwiththefree-particledensityintheplasma.Sothat'splasmaoscillation.Nowwhat'saplasmon?Well,plasmonisasinglequantumofaplasmaoscillation.Sojustlikeaphotonisasinglequantumofelectro-magneticoscillation,asingleplasmonisaquantumofaplasmaoscillation.Thedifferencebetweenelectro-magneticoscillationandplasmaoscillationcomesdowntothisexchangeofenergyhere.Soinaconventionalelectro-magneticoscillation,you'reexchangingenergybetweenelectrostaticpotentialandmagneticpotential,magnetically-storedenergy.Whereasinaplasmaoscillation,youexchangeenergybetweenelectrostaticandkinetic.Andofcoursethere'salsosomemagneticfieldsformedbythecurrenthere.Butit'sthepresenceofthiskineticenergythat'sreallyquitedifferentfromwhatyou'reaccustomedtothinkingaboutinfreespaceforelectromagneticfield.Andthisalsorelatestotheconceptofkineticinductancewhichwe'vetalkedaboutinanotheroneofthesevideos.Sowiththat,we'llfinishfortoday.Ifyouhaveanyquestions,pleasefeelfreetoleavethembelowandI'lldomybesttoanswerthem.PlasmasOscillationsandplasmonsexplained x1.0 x0.5 x0.75 x1.0 x1.5 影片重複 字級大小 快速鍵 返回 175% 150% 125% 100% 90% 字幕與單字 影片操作你可以在這邊進行「影片」的調整，以及「字幕」的顯示 Back Next B2中高級 美國腔 等離子體振盪和質子的解釋。

(plasmaoscillationsandplasmonsexplained) 558 YoungInnting 發佈於 2021年01月14日 更多分享 分享 收藏 回報 影片單字