原子的存在 毕业论文外文及其翻译

《原子的存在 毕业论文外文及其翻译》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、IntroductionAlthoughtheGreekphilosopherDemocritushadpostulatedtheexistenceofatomsinthefirstcenturyBCandDalton’satomictheoryof1807laidthebasisfortheexistenceofatomsbeforetheturnofthetwentiethcentury.Indeed,atthattimeaninfluentialschoolofGermanphysicistsledbyErnstMachconsider

2、edtheatomicmodeltobemerelyausefulpicturewithnobasisinreality.1.1THEEXISTENCEOFATOMSThesituationwasdramaticallychangedbyanexplosionofexperimentalinvestigationoverthefifteenyearsbetween1897and1912.inthe1870s,technicalimprovementsintheconstructionofvacuumpumpshadmadepossibleth

3、einvestigationofelectricalphenomenoninevacuatedtubesandthediscoveryofinvisiblerayswhichtraveledbetweenanelectricallynegativeelectrode(cathode)andanelectricallypositiveelectrode(anode)insuchatube.Theserayscametobeknownascathoderays.Atfirsttherewasconsiderablecontroversyovert

4、heirnature,butaseriesofexperimentscarriedoutbyJ.J.Thomsonin1897demonstratedconclusivelythatthecathoderaysconsistedofastreamofnegativelychargedparticles,presumablyemittedbyatomsinthecathode(Fig.1.1).Thomson’smeasurementsofthedeflectionoftheraysbyelectricandmagneticfieldsenab

5、ledthespeedoftheparticlestobemeasuredandalsotheratioofthechargeofaparticletoitsmass.Bytheturnofthecentury,thecharge-massradiooftheseparticles,whichcametobecalledelectrons,couldbemeasuredtoquitehighprecision.However,togiveabsolutevaluesofthechargeandmass,experimentsofadiffer

6、enttypewererequired.Themostsuccessfulwereinvestigationswheremacroscopicparticlessuchasoildropletswerechargedinsomewayandtheirmotioninelectricfieldsobserved.Arelativelystraightforwardmeasurementofthemassoftheoildropletsenabledthechargeofthechargeoftheelectrontobemeasured.The

7、famousexperimentscarriedoutbyMillikanbetween1909and1916gaveavalueforthischargeas1.592±.002×10-19coulomb,lessthan1percentlowerthanthatacceptedtoday.This,combinedwithThomson’sresults,gaveavaluefortheelectron’smassofapproximately9×10-31kg.Fig.1.1SchematicdiagramofJ.J.Thomson’s

8、cathoderaytubeElectronsemittedbythecathodeareacceleratedthroughtheanode.Thebeamofe