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ID:40022369
大小:574.06 KB
页数:30页
时间:2019-07-17
《4-Electricity Magnetism 12-13》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、UVAPHYSICSDEPARTMENTPHDQUALIFYINGEXAMPROBLEMFILEELECTRICITYANDMAGNETISMUPDATED:DECEMBER4,20131.(a)Computetheelectricfieldandpotentialduetoaninfinitelylongstraightlineofchargeoflineardensity.(b)Nowconsidertwoparallelandoppositelychargedlinesoflinearchargedensitiesand−κseparatedbyvect
2、orgoingperpendicularlyfromthenegativelychargedlinetothepositivelychargedline.Thissystemthereforehasdipolemomentperunitlength.Computethepotentialoftheelectricfieldofsuchadipoleatalocationsatisfyingtheconditionr>>a,whereisatwo-dimensionalvectorinaplaneperpendiculartothelines,theorigin
3、beingatthemidpointofthetwolines.)2.Twoelectronsareseparatedbyadistancerinthex-direction.Assumingtheelectronspinsarebothpointinginthey-direction,determinetheratioofthemagneticinteractionforcebetweentheelectronstotheelectricforcebetweentheelectrons.Howdoesthemagneticforcechangeifoneof
4、thespinsisturnedtopointinthenegativey-direction?Comparethetotalmagneticpluselectrostaticinteractionenergyofthetwoelectronswithparallelspinstothatofelectronswithanti-parallelspins.3.Aphotonofenergyεcollideswithastationaryelectronofmassmandemergesafterthecollisionatanangleθwithrespect
5、tothedirectionofitsoriginalmotion.Computetheenergyofthephotonafterthecollision.Donotassumethattheelectronmotionisnon-relativistic.Whatisthenameoftheeffectdescribedinthisproblem?4.Achargedparticlewithavelocityvistravelinginamediumofpermittivityε.a)(1point)Atwhatthresholdvelocitywillt
6、heparticleemitČerenkovlight?b)(2)DeriveanexpressionfortheangleofemissionoftheČerenkovradiationintermsofthevelocityoftheparticle,andthepermittivity.Ifyouuseagraphicmethodshowyourdiagram(carefullylabeled).1ElectrictiyandMagnetismDecember2013c)(2)Considertwomedia,onewithnandasecondwith
7、nwherenn>.Inwhich1212mediumwillthethresholdvelocityforemissionofČerenkovradiationbelarger?WhichmediumwillhavethelargerČerenkovangleatagivenvelocity?d)(1)IsČerenkovradiationcoherentorincoherent?e)(1)WhatisthestateofpolarizationofČerenkovradiation?Argueforyouranswer.(Hint:rememberthee
8、lectricandmagneticf
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