外文翻译--电路变量和电路元件.doc

文献翻译英文原文：CircuitvariablesandcircuitelementsElectricalandcomputerengineeringareexcitingandchallengingprofessionsforanyonewhohasagenuineinterestin,andaptitudefor,appliedscienceandmathematics.Overthepastcenturyandahalf,electricalandcomputerengineershaveplayeddominantroleinthedevelopmentofsystemsthathavechangedthewaypeopleliveandwork.Satellitecommunicationlinks,telephone,digitalcomputers,televisions,diagnosticandsurgicalmedicalequipment,assembly-linerobots,andelectricalpowertoolsarerepresentativecomponentsofsystemsthatdefineamoderntechnologicalsociety.Asanelectricalorcomputerengineer,youcanparticipateinthisongoingtechnologicalrevolutionbyimprovingandrefiningthereexcitingsystemsandbydiscoveringanddevelopingnewsystemstomeettheneedsofoureve-changingsociety.Webeginourstudywithanoverviewofcircuit.Thisfollowedbyanintroductiontotheconceptofvoltage,current,thebasiccircuitelements,power,andenergy.Nextweintroducebothindependentanddependentvoltageandcurrentsources.Weconcludethisintroductorychapterwithadiscussionofelectricalresistance,ohmlaw,andkirchhoffslaws.1.1circuitanalysis:anoverviewBeforebecominginvolvedinthedetailsofcircuitanalysis,weneedtotakeabroadlookatengineeringdesign,specificallythedesignofelectriccircuit.Thepurposeofthisoverviewprovidesyouwithaperspectiveonwherecircuitanalysisfitswithinthewholeofcircuitdesign.Eventhoughthisbookfocusesoncircuitanalysiswetrytoprovideopportunitiesforcircuitdesignwhereappropriate.Allengineeringdesignwithaneed,asshowninfig.1.1.thisneedmaycomefromthedesiretoimproveonanexistingdesign,oritmaybesomethingbrand-new.Acarefulassessmentoftheneedresultsindesignspecification,whicharemeasurablecharacteristicsofaproposeddesign.Onceadesignisproposed,thedesignspecificationsallowustoassesswhetherornotthedesignactuallymeetstheneed.Aconceptforthedesigncomesnext.Theconceptderivesfromacompleteunderstandingofthedesignspecificationscoupledwithaninsightintotheneed,whichcomesfromeducationandexperience.Theconceptmayberealizedasasketch,asawrittendescription,orkinsomeotherform.Oftenthenextstepistotranslatetheconceptintoamathematicalmodel.acommonlyusedmathematicalmodelforelectricalandcomputersystemsisacircuitmodel.needDesignspecificationsConceptCircuitModelPhysicalPrototypeCircuitanalysisLaboratorymeasurementsCircuitwhichmeetsdesignspecificationsPhysicalinsightFigure1.1aconceptualmodelforelectricalengineeringdesignTheelementsthatcomprisethecircuitmodelarecalledidealcircuitcomponent.Anidealcircuitcomponentisamathematicalofanactualelectricalcomponent,likeabatteryoralightbulb.Itisimportantfortheidealcircuitcomponentusedinacircuitmodeltorepresentthebehavioroftheactualelectricalcomponenttoanacceptabledegreeofaccuracy.Thetoolsofcircuitanalysis,thefocusofthisbook,arethenappliedtothecircuit.Circuitanalysisisbasedonmathematicaltechniquesandisusedtopredictthebehaviorofthecircuitmodelanditsidealcircuitcomponents.Acomparisonbetweenthedesiredbehavior,fromthedesignspecifications,andthepredictedbehavior,fromcircuitanalysis,mayleadtorefinementinthecircuitmodelanditsidealcircuitelements.Oncethedesiredandpredictedbehaviorsareinthecircuitmodelanditsidealcircuitelements,aphysicalprototypecanbeconstructed.Thephysicalprototypeisanactualelectricalsystem,constructedfromactualelectricalcomponents.Measurementtechniquesareusedtodeterminetheactualquantitativebehaviorofthephysicalsystem.Thisactualbehaviorfromcircuitanalysis.Thecomparisonsmayresultinrefinementstothephysicalprototype,thecircuitmodel,orboth.Eventually,thisiterativeprocess,inwhichmodels,components,andsystemsarecontinuallyrefined,mayproduceadesignthataccuratelymatchesthedesignspecificationsandthusmeetstheneed.Fromthisdescription,itisclearthatcircuitanalysisplayaveryimportantroleinthedesignprocess.Becausecircuitanalysisisappliedtocircuitmodels,practicingengineerstrytousematurecircuitmodelssothattheresultingdesignswillmeetthedesignspecificationsinthefirstiteration.Inthisbook,weusemodelsthathavebeentestedforbetween20and100years；youcanassumethattheyaremature.Theabilitytomodelactualelectricalsystemswithidealcircuitelementsmakescircuittheoryextremelyusefultoengineers.Sayingthattheinterconnectionofidealcircuitelementscanbeusedtoquantitativelypredictthebehaviorofasystemimpliesthatwecandescribetheinterconnectionwithmathematicalequations.Forthemathematicalequationstobeuseful,wemustwritethemintermsofmeasurablequantities.Inthecasecircuit,thesequantitiesarevoltageandcurrent,whichwediscussinsection1.2.Thestudyofcircuitanalysisinvolvesunderstandingthebehaviorofeachidealcircuitelementintermsofitsvoltageandcurrentandunderstandingtheconstraintsimposedonthevoltageandcurrentasaresultofinterconnectingtheidealelements.1.2voltage，current,andthebasiccircuitelementsInthecircuittheory,theseparationofchargecreatesanelectricforce(voltage),andthemotionofchargecreatesanelectricfluid(current).Theconceptofvoltageandcurrentareusefulfromanengineeringpointofviewbecausetheycanseparated,energyisexpended.Voltageistheenergyperunitchargecreatedbytheseparation.WeexpressthisratioindifferentialforasV=dw/dq1.1Theelectricaleffectscausedbychargesinmotiondependontherateofchargeflow.Therateofchargeflowisknownastheelectriccurrent,whichisexpressedasI=dq/dt1.2Equation(1.1)and(1.2)aredefinitionsforthemagnitudeofvoltageandcurrent,respectively.Thebipolarnatureofelectricchargerequiresthatweassignpolarityreferencestothesevariables.Wedosointhenextsection.Althoughcurrentismadeupofdiscrete,movingelectrons,wedonotneedtoconsiderthemindividuallybecauseoftheenormousnumberofthem.Rather,wecanthinkofelectronsandtheircorrespondingchargeasonesmoothlyflowingentity.Thus,Iisasacontinuousvariable.Oneadvantageofusingcircuitmodelsisthatwecanmodelacomponentstrictlyintermsofthevoltageandcurrentatitsterminals.Thustwophysicallydifferentcomponentcouldhavethesamerelationshipbetweentheterminals.Wecananalysisitsbehaviorinacircuit.参考译文：电路变量和电路元件对于任何人即便是那些对应用科学和数学有真正兴趣或天赋人来说,电气和计算机工程学是令人振奋和具有挑战性的职业。在过去的一个半世纪里，电气工程师和计算机工程师们在发明创造上扮演致关重要的角色。许多发明出来的系统改变人们工作和生活方式。卫星通信、电话和一些电动工具是当今科技时代中电器系统的典型代表，作为一个参与持续科技革命的电子或计算机工程师,他可以通过提高或改进这些系统,也可以研发或发明新的系统来满足我们日益发展的社会的需要。我们通过对电路原理的概述来开展我们的课程，下面是对电压、电流、基本的电路元件、电源和能量的介绍。随后我们还要介绍独立的和非独立的电压和电流源。这个介绍性的章节从总体上概述了绍基尔霍夫电压定律和基尔霍夫电流定律。1.1电路分析:概述在开始深入电路分析之前,我们需要对电路设计有一个总的认识,尤其是电路的设计部分。这个概述的目的是为你提供一个关于电路分析在整个电路设计中的作用的认识，尽管这本书主要讲的是电路分析，我们也会试图大量的介绍电路设计。所有的工程设计都是为了迎合某种需要而展开的，正如图表1.1所示。这种需要可能会来源于渴望对已经存在的某种产品的改进,也可能来源开发新的东西。对需求的细致评估可以使得这个被提出的设计中的那些可以测量要素的具体化。一旦这个设计被提出来之后,设计的具体化可以使我们评估设计的结果是否满足需求的要求。下面是设计的概念。这个设计的概念源自对设计具体化的彻底的理解和对需求的完全洞悉,同时也源自知识和经验。这个概念可以理解为一个纲领,抑或是明文描述,或者是一些个其他的形式。通常,下一步是将这个概念转化成数学模型，一个适用的电子和计算机系统的数学模型就是一个电路模型。