青蛙悬浮_一个令人惊奇和充满遐思却只需经典物理知识的实验

3010Vol.30No.10201110COLLEGEPHYSICSOct.2011:2010-11-16;:2011-02-27:(1967),,,,,.一个令人惊奇和充满遐思却只需经典物理知识的实验杨晓峰,许丽萍,魏天杰(,030051):,,..,,.:;;;:O441.6:A:10000712(2011)100022032010-(A.Geim)-.,.1997,.,,.!.,.,.,.,,..,.[1].:;:,,;:.,,..4,.,.,,.1842[2],,..,.,.,,.11.1r0,3.,,.,,10,:23,,F(r)dS0,.:F(r0)=0(1)F(r0)0(2)U(r),F=-U(r),(2)2U(r)0.xyz3,.:2U/x20,2U/y20,2U/z20.(2).1.2[3]:,(r),,,2=0.q,U(r)=q(r),F=-U.F=-q2=0,(2).,,,..,,,.:p,E,:U=-pE=-(pxEx+pyEy+pzEz)(3)F=-2U=px2Ex+py2Ey+pz2Ez,E=0,Exy=EyxExz=Ezx,E=0,2Ex=xxEx+yyEx+zzEx=xxEx+yxEy+zxEz=x(E)=0(4)2Ey=0,2Ez=0,F=0,(2),.:V,P=(-0)E,U=-(1/2)VPE(5)F=(1/2)V(-0)2E22E20,E(B)2E2=(E2x+E2y+E2z)=(2ExEx+2EyEy+2EzEz)=2[|Ex|2+|Ey|2+|Ez|2+Ex2Ex+Ey2Ey+Ez2Ez]=2[|Ex|2+|Ey|2+|Ez|2]0(6)F0,.1.3[4]:m,B,U=-mB=-(mxBx+myBy+mzBz)(7)F=(mx2Bx+my2By+mz2Bz)B,B=0.,B=0.(4)B,2Bx=0,2By=0,2Bz=0.F=0,(2)..,.:V,M=-1B,U=-(1/2)VMB=-(1/2)V-1B2(8)F=V-1BB(9)2E20,2B20.,0,F0,;,0,F0,;,=-1,F0,.2,.,,.1778.10-5,,,243010-6.,,,,,!B2,B,,.(16T)[5].(1),(8),BB=B2/2,F=V-1BB.gV,,B2=2g/.,=1gcm-3,g=9.8m/s-2,,=410-7=10-5,B2~2.46103T2m-1.,B2~B2/L,L=10cm,B15.7T.1[3].,B,,=z/L=0.5;,.,(2)[6]:L/2-0.2582azL/2+0.2041a.,L=18cm,a=3.2cm.1(a)(b),=z/L,B,z=0.[6],,.:;;;.,,.,2m,10.,,.,.,.,,,.,,.:[1]BrandtEH.Levitationinphysics[J].Science,1989,243:349354.[2]EarnshawS.Onthenatureofthemolecularforceswhichregulatetheconstitutionoftheluminferousether[J].TransCambPhilSoc,1842,7:97101.[3],.()[M].:,1978:149150,288290.[4],.()[M].:,1978:113119.[5]GeimA.Everyonesmegnetism[J].PhyscisToday,1998,9:3639.[6]BerryMV,GeimA.Offlyingfrogsandlevitrons[J].EurJPhys,1997,18:307313.(41)10,:41,.:[1],.[M].:,2003:190195.[2],.[M].:,2003:261266.[3].[J].,2009,26(6):9698.[4],,,.[J].,2006,26(3):4142.[5],.[J].,2007,20(4):4952.[6],.[J].,2007,27(4):4243.MeasurementofPlancksconstantbychargingcapacitanceHEChunjuan1,WANGLiujiu1,WANGYun2,ZHAOTiesong1(1.DepartmentofPhysics,RenminUniversityofChina,Beijing100872,China;2.DepartmentofPhysics,BeijingUniversityofChemicalTechnology,Beijing100029,China)Abstract:Wedevelopamethodformeasuringthecut-offvoltageofaphotoelectrictubebychargingcapacitancefromthephotocurrentproducedbythephotoelectrictube.Inourexperiment,LEDwithdifferentcolorisusedaslightsources,andadataacquisitionsystemofcomputerisusedformeasuringthecut-offvoltageofthephotoelectrictube.ThedifferencebetweenthemeasuredandthestandardPlanksconstantisfoundtobewithin3%.Keywords:LED;photoelectrictube;Planksconstant;cut-offvoltage;dataacquisition(24)Froglevitation:anastonishingandintriguingexperimentbutonlyrequiringtheknowledgeofclassicalphysicsYANGXiaofeng,XULiping,WEITianjie(DepartmentofPhysics,SchoolofSciences,NorthUniversityofChina,Taiyuan,Shanxi030051,China)Abstract:Byusingthebasicknowledgeofmechanicsandelectromagnetism,wediscussthereasonswhyachargedparticle,electricaldipole,dielectric,magneticdipole,orparamagneticmaterialcannotbesuspendedstablyinafieldandwhyadiamagneticmaterialcan.Further,weintroducethedetailsofthefroglevitationexperiment,whichhasbeencarriedoutbyGeim,anditsbackgroundphysics.Theexplorationsofsuchproblemwillnotonlyintriguestudentsregardingtoitsperspectiveapplicationsbutalsodeepentheirunderstandingtoelectrostaticsandmagnetism.Keywords:froglevitation;diamagnetic;magneticlevitation;stableequilibrium(38)Abstract:TheBoltzmannconstantkBisusedinthenewdefinitionoftemperatureunit-Kelvin.Inthisarticle,thefluorescentspectroscopicmethodisintroducedtodeterminethisconstant.PopulationofelectronsinthermalcoupledlevelsofphosphorscanbedescribedwiththeBoltzmanndistribution.Basedontemperaturedependentphotoluminescenceofaphosphor,theBoltzmannconstantisderivedfromtherelationshipbetweenmeasuredrelativeintensityandtemperature.RelationshipbetweenkBandhc(thePlanckconstantmultiplyinglightspeedinvacuum)isderivedfromexperimentalmeasurement.ThedeterminedBoltzmannconstantshows~0.2%divergenceuponthevaluerecommendedbyCODATAintheyear2006.Keywords:Boltzmannconstant;temperature;fundamentalunit