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《机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 23.ppt》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。
1、Lesson23OHM’SLAWTextDEFINITIONOFOHM’SLAWOhm’slawdescribesmathematicallyhowcurrent,voltage,andresistancearerelated.GeorgOhmdeterminedexperimentallythatifthevoltageacrossaresistorisincreased,thecurrentwillalsoincrease,and,likewise,ifthevoltageisdecreased,thecurrent
2、willdecrease①.Forexample,ifthevoltageisdoubled,thecurrentwilldouble.Ifthevoltageishalved,thecurrentwillalsobehalved.ThisrelationshipisillustratedinFigure23.1,withmeterindicationsofvoltageandcurrent.Ohm’slawalsostatesthatifthevoltageiskeptconstant,lessresistancere
3、sultsinmorecurrent,and,also,moreresistanceresultsinlesscurrent②.Forexample,iftheresistanceishalved,thecurrentdoubles.Iftheresistanceisdoubled,thecurrentishalved.ThisconceptisillustratedbythemeterindicationsinFigure23.2,wheretheresistanceisvariedandthevoltageiscon
4、stant③.FORMULAFORCURRENTOhm’slawcanbestatedasfollows:I=V/R(23-1)ThisformuladescribeswhatwasindicatedbythecircuitsofFigures23.1and23.2.ForaconstantvalueofR,ifthevalueofVisincreased,thevalueofIincreases;ifVisdecreased,Idecreases.AlsonoticeinEquation(23-1)thatifVisc
5、onstantandRisincreased,Idecrease.Similarly,ifVisconstantandRisdecreased,Iincreases.UsingEquation(23-1),wecancalculatethecurrentifthevaluesofvoltageandresistanceareknown.FORMULAFORVOLTAGEOhm’slawcanalsobestatedanotherway.BymultiplyingbothsidesofEquation(23-1)byR,w
6、eobtainanequivalentformofOhm’slaw,asfollows:V=IR(23-2)Withthisequation,wecancalculatevoltageifthecurrentandresistanceareknown.FORMULAFORRESISTANCEThereisathirdequivalentwaytostateOhm’slaw.BydividingbothsidesofEquation(23-2)byI,weobtainR=V/I(23-3)ThisformofOhm’sla
7、wisusedtodetermineresistanceifvoltageandcurrentvaluesareknown④.Remember,thethreeformulasyouhavelearnedinthissectionareallequivalent.TheyaresimplythreedifferentwaysofexpressingOhm’slaw.CALCULATINGCURRENTInthissectionyouwilllearntodeterminecurrentvalueswhenyouknowt
8、hevaluesofvoltageandresistance.Intheseproblems,theformulaI=V/Risused.Inordertogetcurrentinamperes,youmustexpressthevalueofVinvoltsandthevalueofRinohms.EXAMPLE2
