电气工程专业英语section-1-2.ppt

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1、Chapter1FundamentalsofElectricCircuitsSection2CircuitElementsTextNewWordsandExpressionsExercisesEndTranslationStandardSection2CircuitElementsAnelectriccircuitissimplyaninterconnectionoftheelements.Therearetwotypesofelementsfoundinelectriccircuits:passiveelementsan

2、dactiveelements.Anactiveelementiscapableofgeneratingenergywhileapassiveelementisnot.Examplesofpassiveelementsareresistors,capacitors,andinductors.Themostimportantactiveelementsarevoltageorcurrentsourcesthatgenerallydeliverpowertothecircuitconnectedtothem.Section2C

3、ircuitElementsIndependentsourcesAnidealindependentsourceisanactiveelementthatprovidesaspecifiedvoltageorcurrentthatiscompletelyindependentofothercircuitvariables.Anindependentvoltagesourceisatwo-terminalelement,suchasabatteryoragenerator,whichmaintainsaspecifiedvo

4、ltagebetweenitsterminals.Thevoltageiscompletelyindependentofthecurrentthroughtheelement.ThesymbolforavoltagesourcehavinguvoltsacrossitsterminalsisshowninFig.1-4(a).Thepolarityisasshown,Section2CircuitElementsindicatingthatterminalaisuvoltsaboveterminalb.Thusifu>0,

5、thenterminalaisatahigherpotentialthanterminalb.Theoppositeistrue,ofcourse,ifu<0.InFig.1-4(a),thevoltageumaybetimevarying,oritmaybeconstant,inwhichcasewewouldprobablylabelitU.Anothersymbolthatisoftenusedforaconstantvoltagesource,suchasabatterywithUvoltsacrossitster

6、minals,isshowninFig.1-4(b).InthecaseofconstantsourcesweshalluseFig.1-4(a)and1-4(b)interchangeably.Section2CircuitElementsWemightobserveatthispointthatthepolaritymarksonFig.1-4(b)areredundantsincethepolaritycouldbedefinedbythepositionsofthelongerandshorterlines.Fig

7、.1-4Symbolsforindependentvoltagesources(a)usedforconstantortime-varyingvoltage;(b)usedforconstantvoltage(dc).Section2CircuitElementsAnindependentcurrentsourceisatwo-terminalelementthroughwhichaspecifiedcurrentflows.Thecurrentiscompletelyindependentofthevoltageacro

8、sstheelement.ThesymbolforanindependentcurrentsourceisshowninFig.1-5,whereiisthespecifiedcurrent.Thedirectionofthecurrentisindicatedbythearrow.Fig.1-5Sym