外文翻譯——交流電.doc

附錄附錄A外文翻譯原文部分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/.附錄B外文翻譯譯文部分交流電交流電在電路中是一個隨時間變化的值。電流值在任何給定的時間上都是一個瞬態(tài)值，用符號i表示。當(dāng)瞬態(tài)電流值i從用正號標(biāo)記的導(dǎo)體的端流進(jìn)時為正值，而從相反的方向流動時為負(fù)值。當(dāng)電流的任一瞬態(tài)值為正時，它流進(jìn)導(dǎo)體的方向就為正極。假如知道瞬態(tài)值與時間的關(guān)系式：)(t