GRE物理Sub题目精选解答

电磁学1.AFastchargedparticlepassesperpendicularlythroughathinglasssheetofindexofrefraction1.5.TheconeofCerenkovlight,emittedintheglassatangleθ,isincidentontheglass-airinterfaceatthecriticalanglefortotalreflection.Whatisthespeedoftheparticle?answer:c542.answer:D3.answer:E一些简单的量子力学题：1.Aparticleofchargeeandmassmistrappedinaone-dimentionalsquarewellofwidth2awithimpenetrablewalls.Thewallsarelocatedatx=−aandx=a.(1)Ifthequantummechanicalstatesarelabledbyn(n=1isthegroundstate),whatistheexpectationvalueofx^2forverylargen?answer:a^2/3(2)AsmallelectricfieldofstrengthE_0isappliedinthexdirection.Whatisthechangeoftheenergyofthefirstexcitedstateofthisparticleduetothiselectricfield?(Assumethatthetotalpotential,duetothewallsandtheelectricfield,is0atx=0.)answer:02.Thewavefunction)2exp()(22xbAxwhereAandbarerealconstants,isanormalizedeigenfunctionoftheSchrödingerequationforaparticleofmassMandenergyEinaonedimensionalpotentialV(x)suchthatV(x)=0atx=0.DeterminetheformofthepotentialV(x)answer:MxbxV2)(2423.answer:E统计：1.answer:B2.answer:BA一些简单的粒子物理题和狭义相对论1.Thehalf-lifeofamesonatrestis2.5×10-8second.Abeamofmesonsisgeneratedatapoint15metersfromadetector.Onlyhalfofthemesonslivetoreachthedetector.Findthespeedofthemesonanswer:c522.3.Abeamofparticlesisincidentonathintargetofthicknesst.Ifthecrosssectionpernucleusforascatteringoftheparticlesbythenucleioftheofthetargetisσ,andthenumberofnucleiperunitvolumeisn,whatisthefractionofparticlesscattered?answer:ntσ4.Aprotonbeamisincidentonascatterer0.1centimeterthick.Thescatterercontains10^20targetnucleipercubiccentimeter.Inpassingthroughthescatterer,oneprotonperincidentmillionisscattered.Calculatethescatteringcrosssection.answer:10^-25cm^2