atomic, nuclear and quantum physics - welcome to coeur 原子，核和量子物理学-欢迎来到圣心

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1、37TheIBPhysicsCompendium2005:Atomic,nuclearandquantumphysics6.ATOMIC,NUCLEAR&QUANTUMPHYSICSATOMICANDQUANTUMPHYSICS(SECTIONS6.1-6.7) 6.1.Theatomicmodel Duringthe1800stheideathatallmateriaconsistsofatomsgraduallygainedsupport.Itsfundamentalparticlesare,aswetodaydescribeit,theelectrically

2、positiveproton(p+)andneutralneutron(n)whichbothareca2000timesheavierthanthenegativeelectron(e-).Theelectronsoccupycertainlevelsor"shells"outsidethenucleuswiththeprotonsandneutrons.a01a Evidencefortheideathatthepositivechargesintheatomarenotspreadevenlyinit(theThomsonmodel)isgivenbytheG

3、eiger-Marsden(orRutherford)experimentinwhichpositiveparticles(alphaparticlesfromdecayingatoms=heliumnuclei,seelater)areaimedatathingoldfoil.Theresultisthatmostofthempassthroughthefoilwithoutchangingdirection,whilesomebouncebackinalmostthesamedirectionastheycamefrom.Thiscanbecomparedtof

4、iringamachinegunatafencemadeofsolidironbarswithwideopeningsbetweenthem,asopposedtofiringitagainstawoodenfencewithnoopenings. ãThomasIllmanandVasaövningsskola37TheIBPhysicsCompendium2005:Atomic,nuclearandquantumphysics a01b Theradiusofanatomicnucleuscanbefoundbylettingpositiveparticlesw

5、ithaknownkineticenergybescattered(bouncefrom)thenuclei.The"closestapproach"isfoundbyequatingtheirkineticenergywiththeelectricalpotentialdifferencetheyneedtoovercome:a01c·       Kineticenergy:Ek·       Potentialfarfromnucleus:V1=-kqnucleus/r1,wherer1>>0andV1»0.·       Potentialatclosest

6、approachdistancefromcenterofnucleus=V2=-kqnucleus/r2,wherer2=rnucleus.·       Potentialdifference=V1-V2=kqnucleus/rnucleus Workdoneagainstrepulsiveelectricalfieldofnucleus=Ek=qparticleDV=kqparticleqnucleus/rnucleus =>rnucleus=kqparticleqnucleus/Ek ãThomasIllmanandVasaövningsskola37TheI

7、BPhysicsCompendium2005:Atomic,nuclearandquantumphysicsItcanbefoundthattheradiusofthenucleusisfarsmaller(ca10-14m)thanthesizeofthewholeatom(10-10m)whichthereforecanbecomparedtoasolarsystemwithacentralbody(sun/nucleus),smallerbodiesaroundit(planets/electrons)andnothinginbetween.Otherex