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