电路原理课件讲义英文版-Chapter-1

FundamentalsofElectricCircuitsSchoolofAutomationWuhanUniversityofTechnologyLecturer:Dr.LongXiaoLinEmail:[e-mail]:15902716829Whyelectriccircuitstheoryisimportant?FundamentaltheoryuponwhichallbranchesofelectricalengineeringarebuiltGoodmodelforthestudyofenergysystemsingeneralObjective:AnalysisofthecircuitsHowdoesitrespondtoagiveninput?Howdotheinterconnectedelementsanddevicesinthecircuitinteract?StudyMethods:Putinasmucheffortasyoucan(Studythecourseregularly)SolveasmanyproblemsasyoucanAssignments:HomeworkexerciseLabsQuizzesFinalexamNotice:TwohomeworkassignmentscanbemissedCollaborationpolicyHomeworkYoumaycollaboratewithothers,butdoyourownwrite-upLabYoumayworkinateam,butdoyourownwrite-upChapter1BasicConcepts1.1Introduction1.2SystemsofUnits1.3ChargeandCurrent1.4Voltage1.5PowerandEnergy1.6CircuitElements1.7Summary1.1IntroductionBasicConcepts:Charge,Current,Voltage,Circuitelements,Power,EnergyWhatisengineering?PurposefuluseofscienceLumpedcircuitabstractionAnelectriccircuitisaninterconnectionofelectricalelementsAsimpleelectriccircuit1.2SystemsofUnitsThesixbasicSIunitsSI(InternationalSystemofUnits)AninternationalmeasurementlanguageAdoptedbytheGeneralConferenceonWeightsandMeasuresin1960QuantityBasicunitSymbolLengthmetermMasskilogramkgTimesecondsElectriccurrentampereAThermodynamictemperaturekelvinKLuminousintensitycandelacd1.3ChargeandCurrentElectricCurrentisthetimerateofchangeofcharge,measuredinamperes(A)Chargeisanelectricalpropertyatomicparticlesofwhichmatterconsists,measuredincoulombs(C)dqidt0ttqidt☺Adirectcurrent(dc)isacurrentthatremainsconstantwithtime☺Analternatingcurrent(ac)isacurrentthatvariessinusoidallywithtimeDirectionofCurrentFlow:☺Thedirectionofcurrentflowisconventionallytakenasthedirectionofpositivechargemovement☺Basedonthisconvention,acurrentof5Amayberepresentedpositivelyornegatively5APositivecurrentflowNegativecurrentflow1.4VoltageVoltage(orpotentialdifference)istheenergyrequiredtomoveaunitchargethroughanelement,measuredinvolts(V)abdwvdqabbavvababvPolarityofVoltage(1)Pointaisatapotentialofvabvoltshigherthanpointb(2)Thepotentialatpointawithrespecttopointbisvabab9Vab9VNoticeV:dcvoltage(producedbyabattery)v:acvoltage(producedbyanelectricgenerator)Keepinmind:☺Currentandvoltagearethetwobasicvariablesinelectriccircuits☺Electriccurrentisalwaysthroughanelement☺Electricvoltageisalwaysacrosstheelementorbetweentwopoints1.5PowerandEnergyInstantaneouspower:time-varyingquantityPoweristhetimerateofexpendingorabsorbingenergy,measuredinwatts(W)dwpdtdwdwdqpvidtdqdtorpviPassivesignconventionissatisfiedwhenthecurrententersthroughthepositiveterminalofanelementandp=+vi.Ifthecurrententersthroughthenegativeterminal,p=-vivpviivpviiLawofconservationofenergy:Powerabsorbed=-Powersupplied0orpEnergyisthecapacitytodowork,measuredinjoules(J)00ttttwpdtvidtNotice:Theelectricpowerutilitycompaniesmeasureenergyinwatt-hours(Wh)13,600WhJ1.6CircuitElementsPassiveelementsActiveelementsResistorsInductorsCapacitorsGeneratorsBatteriesThemostimportantactiveelements:IndependentsourceDependentsourceVoltagesourceCurrentsourceCCCSCCVSVCVSVCCSAnelementisthebasicbuildingblockofacircuitAnidealindependentsourceisanactiveelementthatprovidesaspecifiedvoltageorcurrentthatiscompletelyindependentofothercircuitvariablesvViAnidealdependent(orcontrolled)sourceisanactiveelementinwhichthesourcequantityiscontrolledbyanothervoltageorcurrentviVCVS:Avoltage-controlledvoltagesourceCCVS:Acurrent-controlledvoltagesourceVCCS:Avoltage-controlledcurrentsourceCCCS:Acurrent-controlledcurrentsource1.7Summary1.Anelectriccircuitconsistsofelectricalelementsconnectedtogether2.TheInternationalSystemofUnits(SI)istheinternationalmeasurementlanguage,whichenablesengineerstocommunicatewiththeirresults.Fromthesixprincipalunits,theunitsofotherphysicalquantitiescanbederived.3.Currentistherateofchargeflow.4.Voltageistheenergyrequiredtomove1Cofchargethroughanelement.dqidtdwvdq5.Poweristheenergysuppliedorabsorbedperunittime.Itisalsotheproductofvoltageandcurrent.6.Accordingtothepassivesignconvention,powerassumesapositivesignwhenthecurrententersthepositivepolarityofthevoltageacrossanelement.7.Anidealvoltagesourceproducesaspecificpotentialdifferenceacrossitsterminalregardlessofwhatisconnectedtoit.Anidealcurrentsourceproducesaspecificcurrentthroughitsterminalsregardlessofwhatisconnectedtoit.8.Voltageandcurrentsourcescanbedependentorindependent.Adependentsourceisonewhosevaluedependsonsomeothercircuitvariable.dwpvidt