外文翻译——交流电.doc

附录附录A外文翻译原文部分AlternatingCurrentAnalternatingcurrentisonewhichvariesinthecircuitwithtime.Thevalueofthecurrentatanygiveninstantoftimeistheinstantaneousvalueofcurrent,symbolizedbyi.Theinstantaneousvalueofcurrentiisdeemedpositiveforonedirectionofflowthoughthecross-sectionofaconductor,andnegativefortheoppositedirection.Thedirectionofcurrentflowinwhichinstantaneousvaluesarepositiveiscalledpositive.Acurrentisfullyspecified,ifoneknowsitsinstantaneousvalueasafunctionoftime,i=F(t),anditspositivedirection.Currentwhosevaluerecurforequalincrementsoftimearecalledperiodic,andtheleastincrementoftimeforwhichthisrecurrenttakesplaceiscalledtheperiodT.Foraperiodiccurrenti=F(t)=F(t+T)Fig.4.1showsanexampleoftherelationshipi=F(t)foraperiodiccurrent.Thearrowinthediagramindicatesthepositivedirectionofcurrentflow.Thedottedarrowsshowtheactualdirectionofcurrentflowattheinstantsoftimewheni0andi0,thestart(orzeropoint)ofthesinusoid1iisshiftedtotheleft,andfor20itisshiftedtotherightoftheoriginofcoordinates.Alternatively,theinstantaneousvalueofasinusoidalcurrentmayberepresentedbyacosinusoidalfunctionoftheformtIimcos()Where2/.Whentwoormoresinusoidalfunctiondifferintimephaseasreckonedfromsimilarpoints,theyaresaidtobeshiftedordisplacedinphasewithrespecttooneanother.Thisphaseshift,orthephasedisplacement,ismeasuredbetweentheirrespectivezeros,andobviouslyisthedifferenceinepochangles.ReferringtoFig.4.3,021,andthecurrent1iissaidtoleadthecurrent2iinphaseby21,or,whichisthesame,thecurrent2ilagsinphasebehindthecurrent1iby21.Twosinusoidalfunctionsofthesamefrequencyaresaidtobeinphaseiftheyhavesameepochangle,andaresaidtobeinanti-phasewhentheirphasedisplacementis.Finally,theyaresaidtobeinquadratureiftheirdifferenceis2/.附录B外文翻译译文部分交流电交流电在电路中是一个随时间变化的值。电流值在任何给定的时间上都是一个瞬态值，用符号i表示。当瞬态电流值i从用正号标记的导体的端流进时为正值，而从相反的方向流动时为负值。当电流的任一瞬态值为正时，它流进导体的方向就为正极。假如知道瞬态值与时间的关系式：)(t