Joseph John Thomson

ThesynonymThomson(thewinneroftheNobelPrizeinPhysics)generallyreferstoJosephJohnThomson

CharacterRelationship

Errorcorrection

Turnofferrorcorrection

• SonGeorgePageThomson

  Anerror5823322hasbeenreported

Character'slife

BorninManchester,EnglandonDecember18,1856,Hisfatherwasabusinessmanwhospecializedinprintinguniversitytextbooks.Duetohisprofession,hisfathermetsomeprofessorsattheUniversityofManchester.Thomsonwasinfluencedbyscholarssincehewasachildandstudiedveryseriously.HeenteredtheUniversityofManchesterattheageoffourteen.Duringhisuniversitystudies,hewasunderthecarefulguidanceofProfessorSituHua,coupledwithhisownassiduousstudy,andhisstudiesimprovedrapidly.

In1876,attheageof21,hewasrecommendedtotheTrinityCollegeofCambridgeUniversityforfurtherstudy.

In1880,hetookthedegreeexaminationoftheUniversityofCambridgeandobtainedhisdegreewithsecondplace.HewasthenselectedasastudentofTrinityCollege,andtwoyearslaterhewasappointedasauniversitylecturer.Hehasahighlevelofaccomplishmentinmathematicalphysics.Publishedpapers"OntheMotionofVortexRings"and"OntheApplicationofDynamicsinPhysicsandChemistry".

In1884,28-year-oldThomsonwasrecommendedbyRayleighasaprofessorofphysicsintheCavendishLaboratory.

In1897,Thomsonprovedtheexistenceofelectronsandmeasuredthecharge-to-massratioofelectronsinhisexperimentsonraregasdischarges,whichcausedasensationintheentirephysicscommunity.

In1905,hewasappointedasaprofessorattheRoyalAcademy;

WontheNobelPrizeinPhysicsin1906;

In1916,hewasappointedasthePresidentoftheRoyalSociety.

In1919,hewaselectedastheheadoftheForeignNationalCommitteeoftheAcademyofSciences.Duringhis34yearsasCavendishProfessorofExperimentalPhysicsandLaboratoryDirector,Thomsonwasfullofpeachesandplums.

OnAugust30,1940,ThomsondiedinCambridge.Heis84yearsold.

In1858,GeislerinGermanymadealow-pressuregasdischargetube.

In1859,PruckerofGermanyusedaGeislertubetoconductadischargeexperimentandsawagreenglowontheglasstubewallfacingthecathode.

In1876,GoldsteinofGermanyproposedthattheglowontheglasswalliscausedbyacertainkindofrayproducedbythecathode,whichhenamedthecathoderay.Whatisthecompositionofcathoderays?Attheendofthenineteenthcentury,somescientistssaiditwasanelectromagneticwave;somesaiditwascomposedofchargedatoms;somesaiditwascomposedofnegativelychargedparticles.Thereweredifferentopinions,andnoacceptedconclusioncouldbereachedatthemoment.ThedebatebetweenBritishandFrenchscientistsandGermanscientistsoverthenatureofcathoderayshaslastedformorethantwodecades.

Finally,in1897,beforeThomson'sexcellentexperimentalresults,thetruthwasrevealed.TheprocessofThomson’sexperimentwaslikethis.Heplacedasmallpieceofglasscoatedwithzincsulfideonthepathofthecathoderay,andsawthatzincsulfideflashed.Thisshowsthatzincsulfidecanshowthe"track"ofthecathoderay.Hefoundthatundernormalcircumstances,thecathoderaystravelinastraightline,butwhenanelectricfieldisappliedtotheoutsideofthefiringtube,orahoof-shapedmagnetisplacedontheoutsideofthetube,itturnsoutthatallthecathoderaysaredeflected..Accordingtothedirectionofitsdeflection,itisnotdifficulttodeterminethenatureofthecharging.Thomsonconcludedin1897:These"rays"arenotetherwaves,butnegativelychargedmatterparticles.Butheaskedhimself:"Whataretheseparticles?Aretheyatomsormolecules,ormatterinafinerstateofequilibrium?"Thisrequiresmoreelaborateexperiments.Atthattime,thingssmallerthanatomswerenotknown,soThomsonassumedthatitwasanionizedatom,thatis,anegativelycharged"ion."Hewantedtomeasurethemassofthis“ion”.Tothisend,hedesignedaseriesofsimpleandingeniousexperiments:First,asingleelectricormagneticfieldcandeflectachargedbody,andtheforceexertedbyamagneticfieldonaparticleisRelatedtothespeedofparticles.Thomsonappliesanelectricandmagneticfieldtotheparticlesatthesametime,andadjuststhemsothatthedeflectionoftheparticlescausedbytheelectricfieldandmagneticfieldcanceleachotherout,sothattheparticlesstillmoveinastraightline.Inthisway,thevelocityoftheparticlescanbecalculatedfromtheratiooftheintensityoftheelectricfieldandthemagneticfield.Oncethevelocityisfound,theratioofthechargetothemassoftheparticlecanbemeasuredbymagneticdeflectionorelectricaldeflectionalone.Thomsonusedthismethodtodeterminetheratioofchargetomassof"particles".Hefoundthatthisratiohasnothingtodowiththenatureofthegas,anditismuchlargerthantheratioofhydrogenionsintheelectrolyte(whichisthelargestknownamountatthetime).Thisshowsthatthemassofthisparticleismuchsmallerthanthemassofhydrogenatoms.Theformerisaboutonethousandthofthelatter.

Later,theAmericanphysicistRobertMillikanaccuratelymeasurednewresultsintheoildropexperimentfrom1913to1917.Theformerwas1836thofthelatter.TheresultofThomson'smeasurementconfirmspositivelythatthecathoderayiscomposedofelectrons.Forthefirsttime,humanshaveconfirmedtheexistenceofakindof"elementaryparticles"-electrons.Thename"electron"wasadoptedbythephysicistStoneyin1891.Theoriginalintentwastodeterminethenameofabasicunitofelectricity.Later,thetermwasusedtomeanthe"particles"discoveredbyThomson.Sincethediscoveryofelectrons,Thomsonhasbecomeaninternationallyrenownedphysicist.Priortothis,itwasgenerallybelievedthatatomswere"indivisible"things.Thomson'sexperimentpointedoutthatatomsarecomposedofmanyparts.Thisexperimentmarkedaneweraofscience.Peoplecallhim"agreatmanwhofirstopenedthedoortoelementaryparticlephysics."

In1905,hewasappointedasaprofessorattheRoyalAcademy;in1906,hewasawardedtheNobelPrizeinPhysics;andin1916,hewasappointedPresidentoftheRoyalSociety.Hedidnotstopbecauseofthis,andcontinuedtoclimbthepeakofscienceasalways.Thomsonisbothatheoreticalphysicistandanexperimentalphysicist.Theexperimentshehasdoneinhislifecannotbecalculated.Itwasthroughrepeatedexperimentsthathemeasuredthecharge-to-massratioofelectronsanddiscoveredelectrons.Intheexperiments,hecreatedamethodtoseparateatomsofdifferentmasses,whichprovidedaneffectivemethodforlatergenerationstodiscoverisotopes.Duringhis34yearsasCavendishProfessorofExperimentalPhysicsandlaboratorydirector,Thomsonsetouttoupdatethelaboratory,introducenewteachingmethods,andfoundedanextremelysuccessfulresearchschool.

UniversityofManchester(2photos)

SuccessivenewdiscoveriesgushoutfromCavendishLablikeatide:theelectroniccloudchamber,partoftheachievement.Thelaboratoryhastrainedmanytalents.Rutherford,C.T.R.Wilson(C.T.R.Wilson),R.J.Strutt(R.J.Strutt),F.W.Aston(F.W.Aston),G.I.Taylor(GITaylor),andhissonG.P.Thomson(G.P.Thomson),bothstudentsofThomson,theyhavebecomefamousscientists.Amonghisstudents,ninehavewontheNobelPrize.Thomsonisverystrictwithhisstudents.Herequiresstudentstolearntherequiredexperimentaltechniquesbeforestartingtodoresearch.Alltheinstrumentsusedintheresearchmustbemadebyyourself.Hebelievesthatuniversitiesshouldbeaplacetotraintalentswhocanthinkandworkindependently,notafactorythatuses"off-the-shelfmachines"toproject"deadproducts".Therefore,heinsistedonnotallowingstudentstouseready-madeinstruments,andherequiredstudentstobenotonlytheobserversofexperiments,butalsothecreatorsofexperiments.Thomsonhaswrittenmanybooks.Suchas"ModernResearchonElectricityandMagnetism","BasicTheoryofElectricityandMagnetism"andsoon.Afterhebecamefamous,manycountriesinvitedhimtogivelectures,butheneveragreedeasily.Forexample,thefamousPrincetonUniversityintheUnitedStatesonceaskedhimtogivelectures,butintheendheagreedtogivelecturesforsixhours.Thecontentheteachesisquiteimportantandhasacertainvaluetonuclearphysics.Thisisenoughtoshowthatheisveryrigorousinhisacademicstudies.Roentgenshockedtheworldbecauseheannounced"anewkindofray"andperformedwhathisraycando.

OnAugust30,1940,ThomsondiedinCambridge.HisasheswereburiedinthecenterofWestminsterAbbey,togetherwiththeashesofgreatscientistssuchasNewton,Darwin,andKelvin.

Significantcontribution

JosephJohnThomsonisfamousforhisexperimentsonelectronsandisotopes.HeisthethirddirectorofCavendishLaboratory.AportraitofhimworkingonacathoderaytubehangsintheMaxwelllecturehallofthelaboratory.Itseemsthatheisnotgoodatspecificoperations,buthisunderstandingoftheworkingprincipleoftheinstrumentisveryagile.

J.J.ThomsonheardsomeofMaxwell’slectures,andundertheguidanceofLordRayleigh,Maxwell’ssuccessorasProfessorCavendish,Thomsoncompletedseveraltheoreticalpapers.In1884,RayleighfollowedhisoriginalPromise(foronlyfiveyears)resignedfromthepositionofProfessorCavendish.WhenThomsonappliedforthisposition,hestated:"Ididn'tseriouslyconsiderthejobandtheresponsibilities"heapplied.Hewasonly28yearsoldanddidnotexpecttobeelected,buthewaselectedtohissurprise.Theseelectorsareeitherveryluckyorveryfar-sighted.Thomsonsaid:"Ifeellikeafisherman.Withalightweightfishingtackle,Ithrewalineoffishinglineinanunexpectedplaceandcaughtafish.Thefishwastooheavytomakethisfisherman.Peoplecan’thangittotheshore.Ithinkit’sdifficulttoreplacesomeonewithareputationlikeLordRayleigh.”It’sworthnotingthathedoesn’tmentionMaxwell,althoughThomsontalkedaboutthefirstplaceelsewhere.AppointmentofProfessorCavendish(February1871):

ItisbelievedthattheschoolfirstdiscussedwithSirWilliamThomson(laterLordKelfin)andthenwiththegreatGermanphysicistDiscussedwiththebiologistvonHelmholtz,buttheyallthoughttheycouldnotaccepttheposition.WhenMaxwellwaselected,hisworkwasonlyunderstoodbyfewpeople,andtheauthenticityofhissupremecontributiontophysics—thetheoryofelectromagneticfields—isstillanopenquestion.Thomsonsetouttoupdatethelaboratory,introducenewteachingmethods,andcreateanextremelysuccessfulresearchschool.AseriesofnewdiscoveriesfloodedoutofCavendish’slaboratorylikeatide:electronics,cloudchambers,importantearlyworkonradioactivity,andisotopes,thesearethemostexcitingRutherford,C.T.R.Wilson(C.T.R.Wilson),R.J.Strutt(RJStrutt,sonofLordRayleigh),J.StruttS.E.Townsend(J.S.E.Townsend),C.G.Barkla(C.G.Barkla),O.W.Richardson(O.W.Richardson),F.W.Aston(F.W.Aston),G.I.Taylor(GITaylor),andG.I.P.Thomson(G.P.Thomson),allhisstudents,theyhavebecomefamousscientists.

ThediscoveryofRoentgen’sX-raysgaveanewmethodofgasionizationandprovidedanewinsightintothebehaviorofgasions.Thomsonbeganresearchinthatdirection,whichledtothestudyoffreeelectrons.

In1897,Thomsonconfirmedtheparticulatenatureofcathoderaysandmeasuredthevelocityandcharge-to-massratiooftheparticles.InthetwotubesusedbyThomsoninhisexperiment,theraysareemittedfromthecathodeAontheleftsideofthetubeandenterthesecondtubethroughaslitintheanodeB.AmagnetcanbeusedtodeflecttheraysintoaFaradaycage.Thecollectedchargeisnegative.Therefore,itisprovedthatthecathoderaysarenegativelychargedparticles.SimilarexperimentshavebeendonebyJPerrininFrance.Inasecondtypeoftube,thecathoderaysproducedbyCpassthroughthegroundedslitsAandB,forminganarrowbeamofraysthathittheotherendofthetube.Asmallbrightspotofphosphorescenceappearswheretherayshitthebulb-likeendfaceofthetube.

WhenThomsonconnectedthetwometalplatesEandDtothetwoendsofthebattery,thephosphorspotmoved,provingthatthecathoderaysweredeflectedbytheelectricfield.Withamagneticfieldperpendiculartotheelectricfield,hecandeflecttheraysmagnetically.Magneticdeflectionhasbeenobservedbefore,butJ.J.Thomsonwasthefirstpersontoobserveelectricaldeflection.Theelectricaldeflectionofthecathoderayisobviouslylacking,whichpromotesJ.J.Thomson’sprimaryfactorinconductingthisresearch.Whyhasn'tanyonediscoveredthedeflectionofelectricityinthedecadesthatcathoderayshavebeenstudied?Thereasonissimple:unlessthereisagoodvacuuminthecathoderaytube,theelectricfieldcannotbeestablished.Lowvacuumisanelectricalconductorinwhichanelectrostaticfieldcannotbeestablished.ButThomsonsucceeded,notonlywiththedevicebutalsowiththeothertwodevices.InAugust1897,hedescribedanexperiment"totestthetheoryofchargedparticles"andappliedhismeasurementstodeterminethecharge-to-massratiooftheparticlesthatmakeupthecathoderay.Fromthesameexperiment,healsoderivedthevelocityoftheparticles.Hereisasummaryofhisreasoning:thetotalamountofelectricityQcarriedbyagivencurrentisequaltothenumberofallitsparticlesNtimesthechargeeofeachparticle:

Ne=Q

Then,measuretheenergyWtransmittedbytheparticlesbymeasuringtheheatgenerated.Thisvaluemustbeequaltothekineticenergyoftheparticleswithmassmandvelocityv

1/2Nmυ²=W

1/2Nmυ²=W

1/2Nmυ²=W

1/2Nmυ²=W

p>

Usemagneticmethodstodeflectparticles.Heknows:

mv/e=Bp

HerepistheradiusofcurvatureoftheorbitandBisthemagneticfield.Becauseenergy,electricity,magneticfieldandradiusofcurvaturearemeasurable,hecaninferthat

e/m=2W/(Q²B²p²)

hasavalueof2.3×10¹⁷(electrostaticunitelectricity/g),muchlargerthanthecharge-to-massratioe/mofionsintheelectrolysismethod.

Inhis1897article,Thomsondescribedanothernoteworthyobservation:theparticlesthatmakeupthecathoderaysareallthesame,regardlessofthecathodeinthetubeorthecompositionofthecathodeorgas.Thereisauniversalcompositionofallsubstances.

Later,in1899,heusedhispaststudentC.T.R.ThetechnologyandideasdevelopedbyWilsonmeasurethechargeandmassofelectronsrespectively.Wilsonhasnoticedthatundersuitablecircumstances,thechargeactsasacondensationnucleusforsupersaturatedsteam.Becausewaterwillcondenseonthem,thishelpstheformationofmist.Insuchamistformedbythepresenceofelectriccharge,onecanmeasurethevolumeofsmallmistdropletsbasedonthespeedatwhichtheyfall,andcalculatetheirnumberfromthetotalamountofprecipitatedwaterorbasedontheinitialsupersaturatedvapor.Accordingtothisdata,thenumberofallthedropletsinthefogcanbeobtained.Accordingtothetotalchargetransferredbythemist(whichisdirectlymeasurable),itcanbefoundthatonaverage,thechargeoneachdropletisthesameastheelectroniccharge.InthisworkdoneinCavendish’slaboratory,theelectronchargeobtainedisapproximately3×10^-10absoluteelectrostaticunits.Accordingtothemeasurede/mvalue,theelectronqualitycanbeobtained.

This"dropping"methodwaslateradoptedbyR.A.Millikan(RAMillikan)(1910)improveditintheUnitedStates.Insteadofobservingthefog,heobservesindividualdroplets;hetransformsthismethodintoaprecisemethodandobtainsanelectronicchargeof4.78×10^-10esu.Thishasbeenthebestdirectmeasurementformanyyears.However,in1929,toeveryone'ssurprise,itwasdiscoveredthatithadanerrorof1%,whichwasmuchlargerthantheestimatederror.Theoriginofthisdifferenceliesinthemeasurementofairviscosity.Theaccuracyoftheelectronchargevalueknowntodayis3partspermillion,whichis4.803242×10^-10esu;theknownaccuracyof6partspermillione/mis5.272764×10^-17esu/g.

Roentgenshockedtheworldbecauseheannounced"anewkindofray"andperformedwhathisraycando.

Overviewofelectrons

Anelectronisanelementaryparticlewhoseweightis1/1836ofaproton.Electronsmoveathighspeedsaroundthenucleus.Electronsareusuallyarrangedoneachenergylayer.Whenatomscombinewitheachothertoformmolecules,theelectronsintheoutermostlayerwillmovefromoneatomtoanotherorbecomesharedelectrons.ThisisawordcreatedbyIrishphysicistGeorgeDingStoneyin1891basedontheelectric+-on"son"ofelectricity.Electronsbelongtotheclassofleptoninsubatomicparticles.Leptonisconsideredtobeoneofthebasicparticlesthatmakeupmatter,thatis,itcannotbebrokendownintosmallerparticles.Ithas1/2spin,whichisanotherkindoffermion(accordingtoFermi-Diracstatistics).

Thechargeoftheelectronise=1.6×10-19Coulombs,andthemassis9.10×10^-31kg(0.51MeV/c2).Usuallyexpressedase^-.Theantiparticleofanelectronisapositron,whichhasthesamemass,spinandequalpositivechargeastheelectron.Thebasicunitofmatter-theatomiscomposedofelectrons,neutronsandprotons.Comparedwiththenucleuscomposedofneutronsandprotons,themassofelectronsisextremelysmall.Themassofaprotonisapproximately1,840timesthatofanelectron.Whenanelectronisfreefromthebondageofthenucleusandmovesfreelyinotheratoms,thenetflowphenomenonitproducesiscalledelectriccurrent.Staticelectricityreferstoasituationinwhichanobjecthasmoreorlesselectricitythanthenucleus,resultinginanimbalancebetweenpositiveandnegativeelectricity.Whenthereareexcesselectrons,itissaidthattheobjectisnegativelycharged;whentherearenotenoughelectrons,itissaidthattheobjectispositivelycharged.Whenthepositiveandnegativeelectricitybalances,theobjectissaidtobeelectricallyneutral.Therearemanyapplicationmethodsofstaticelectricityinourdailylives.Anexampleisaninkjetprinter.

Theelectronwasdiscoveredin1897byJosephThomsonoftheCavendishLaboratoryattheUniversityofCambridgewhilestudyingcathoderays.Itcanonlybeexploredoutsidethenucleus.Itisattributedtoagroupoflow-massmatterparticlescalledleptons,whicharesettohaveanegativeunitcharge.Theelectronsaresmallandlight(205timeslighterthanmuons),andareclassifiedasleptoninsubatomicparticles.Leptonisaclassofmatterclassifiedaselementaryparticles.Theelectronhas1/2spinandsatisfiestheconditionoffermions(accordingtoFermi-Diracstatistics).Electronsdonuclearmotionintheatom.Thegreatertheenergy,thefartherawayfromthetrajectoryofnuclearmotion.Thespacewhereelectronsmoveiscalledtheelectronlayer.Thefirstlayercanhaveupto2electrons,thesecondlayercanhaveupto8electrons,thenthlayercanholdupto2n²electrons,theoutermostlayercanholdupto8electrons,andthelastlayercanholdupto8electrons.Thenumberofelectronsdetermineswhetherthechemicalpropertiesofasubstanceareactive.Electrons1and2aremetallicelements,3,4,5,6,7arenon-metallicelements,and8areraregaselements.Theelectronsofasubstancecanbelostorobtained.Thepropertyofasubstancetogainelectronsiscalledoxidizingproperty,andthesubstanceisanoxidizingagent;thepropertyofasubstancetoloseelectronsiscalledreducingproperty,andthesubstanceisareducingagent.Theoxidizingorreducingpropertyofasubstanceisdeterminedbythedifficultyofgainingorlosingelectrons,andhasnothingtodowiththenumberofelectronsgainingorlosing.