电气工程与自动化专业英语PPT课件.ppt

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1、Chapter1FundamentalsofElectricCircuitsSection2CircuitElementsTextNewWordsandExpressionsExercisesEndTranslationStandardSection2CircuitElementsAnelectriccircuitissimplyaninterconnectionoftheelements.Therearetwotypesofelementsfoundinelectriccircuits:passiveelementsandact

2、iveelements.Anactiveelementiscapableofgeneratingenergywhileapassiveelementisnot.Examplesofpassiveelementsareresistors,capacitors,andinductors.Themostimportantactiveelementsarevoltageorcurrentsourcesthatgenerallydeliverpowertothecircuitconnectedtothem.Section2CircuitEl

3、ementsIndependentsourcesAnidealindependentsourceisanactiveelementthatprovidesaspecifiedvoltageorcurrentthatiscompletelyindependentofothercircuitvariables.Anindependentvoltagesourceisatwo-terminalelement,suchasabatteryoragenerator,whichmaintainsaspecifiedvoltagebetween

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

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

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

7、tvoltagesources(a)usedforconstantortime-varyingvoltage;(b)usedforconstantvoltage(dc).Section2CircuitElementsAnindependentcurrentsourceisatwo-terminalelementthroughwhichaspecifiedcurrentflows.Thecurrentiscompletelyindependentofthevoltageacrosstheelement.Thesymbolforani

8、ndependentcurrentsourceisshowninFig.1-5,whereiisthespecifiedcurrent.Thedirectionofthecurrentisindicatedbythearrow.Fig.1-5Sym