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首页 Chapters 254 and 26 to 263

Chapters 254 and 26 to 263.ppt

Chapters 254 and 26 to 263

中小学精品课件
2019-05-19 0人阅读 举报 0 0 0 暂无简介

简介:本文档为《Chapters 254 and 26 to 263ppt》,可适用于工程科技领域

ChaptersandtoHowcurrentflowsxEMFElectromotiveForceAnychemical,solar,mechanical,heatmethodofcreatingapotentialdifferenceBatteriesAlternator,dynamoSolarcell,photovoltaicThermocoupleSymbolEUnits:voltsAsimplecircuitiEMFDevicesIdealEMFdevice–nointernalresistanceRealEMFdevice–someinternalresistanceBatteriesSeveralDifferentTypesofBatteries(calledcells)WetCell(left)CarBatteriesHighCurrentAppsDryCells(ZnCupaste)DryCellRatingsAAAmAAAmACmADmAAkalineCellsAAAmAAAmACmADmAEMF=VCellsareconstantvoltagesources:VPbOPbOPbOPbPbPbHSOPbSOeePbSOInternalResistanceThebatteryitselfcanhavesomeresistancetocurrentflowCouldbeterminalsCouldbeplatesorpasteCouldbecombinationPbOPbOPbOPbPbPbHSOInternalResistanceWetreattheinternalresistanceasifanexternalresistorhadbeenaddedtothecircuitjustaheadofthepositiveterminalTerminalVoltage(EffectiveVoltage)EMFRvavbVab=VaVb=EMFiRLoopRuleThealgebraicsumofchangesinpotentialencounteredinacompletetraversalofthecircuitmustbezeroAKAKirchoff’sLoopRuleConsiderNashvillePanamaCityTotalElevationChange=FromanelectricalperspectiveResistanceruleForamovethrougharesistorinthedirectionofcurrent,thechangeinpotentialis–iRIfthemoveopposesthecurrentthenthechangeinpotentialisiRimoveVaVbVaVb=iRVaVb=iREMFRuleForamovefromthenegativeterminaltothepositiveterminalthenthechangeinpotentialisEMFForamovefrom“”to“”thenthechangeinpotentialisEMFmoveEMFEMFPuttingtheseideasintopracticeiechangingacircuitintoanequationR=WEMF=VPickadirectionforthecurrentPickadirectionofcircuittraversalSumthepotentialsasyoutraversethecircuitiMymoveXFromX,iREMF=EMF=iR=ii=AormAThenegativesignmeansthatweguessedthewrongdirectionforthecurrentResistorsinSeriesConnectedresistancesaresaidtobeinserieswhenapotentialdifferencethatisappliedacrosstheircombinationisthesumoftheresultingpotentialdifferencesacrossalltheresistancesRRREEiRiRiR=ReqESoReq=RRRReducingNetworks,IfYouCan,thenDOSO!AlwaystrytoreducethetotalnumberofvariablesbyusingtheequivalentresistanceForNresistorsinseries,theequivalentresistanceisReq=RR…RNHowtofindapotentialdifferenceTofindthepotentialdifferencebetweenanytwopointsStartatonepointTraversethecircuitfollowinganypathAddalgebraicallythechangesinpotentialRRREPointAPointBBlueVa–iRiR=VbVaVb=i(RR)iRedVaEiR=VbVaVb=EiROnelastwordoninternalresistanceRecallPower,P=ViErEir=VairE=VbVaVb=EirP=iV<(VaVb)P=i(Eir)P=EiirXXabiPowerofEMFDeviceThermaldissipation(losses)JunctionRuleSumofallcurrentsenteringajunctionmustequalthesumofallcurrentsleavingthejunctioniiiiiiiiiii=iii=iiii=IN=OUTResistorsinParallelConnectedresistancesaresaidtobeinparallelwhenapotentialdifferencethatisappliedacrosstheircombinationresultsinthatsamepotentialdifferenceacrosseachresistanceERRRReqEEiiiiii=iiiResistorColorCodesColorCodesColorValueToleranceBlackBrownRedOrangeYellowGreenBlueVioletGrayWhiteGoldSilverNoColorTBand*Bandx^BandBandTGuidelinesforProblemSolvingReplacenetworkofresistorswiththeirequivalents(ifpossible)Ifyoucan’tsimplifytoasingleloop,thenusethejunctionruleandtheloopruletosetupaseriesofequationsBesureto:Pickadirectionofcurrent(signisamathematicalconvention)IfyoutraversearesistoragainstthecurrenttheniRelse–iRIfyoutraverseanEMFsourcefromlowpotentialtohighpotentialthentheEMFispositive,elsenegativeYouhavethefollowingarbitrarychoicesDirectionsofcurrentsWhichloopstouseDirectionoftraversalofeachloopStartingpointandendingpointABOVEALL,REMEMBER:TRAVERSETHELOOPCOMPLETELYONCEYOUHAVECHOSENADIRECTIONOFTHECURRENTYOUMUSTSTICKWITHTHISDIRECTIONUNTILYOUHAVEFINISHEDTHEPROBLEM

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