物理学基础_-_Fundamentals_of_Physics_28_Direct_Current_Circuits

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1、PPUZZLERUZZLERIfalltheseapplianceswereoperatingatonetime,acircuitbreakerwouldproba-blybetripped,preventingapotentiallydangeroussituation.Whatcausesacir-cuitbreakertotripwhentoomanyelec-tricaldevicesarepluggedintoonecir-cuit?(GeorgeSemple)chapterDirectCurrentCircuitsChapterOutline28.

2、1ElectromotiveForce28.5(Optional)ElectricalInstruments28.2ResistorsinSeriesandinParallel28.6(Optional)HouseholdWiringand28.3Kirchhoff’sRulesElectricalSafety28.4RCCircuits86828.1ElectromotiveForce869hischapterisconcernedwiththeanalysisofsomesimpleelectriccircuitsthatcontainbatteries,

3、resistors,andcapacitorsinvariouscombinations.TheanalysisTofthesecircuitsissimplifiedbytheuseoftworulesknownasKirchhoff’srules,whichfollowfromthelawsofconservationofenergyandconservationofelectriccharge.Mostofthecircuitsanalyzedareassumedtobeinsteadystate,whichmeansthatthecurrentsarec

4、onstantinmagnitudeanddirection.InSection28.4wedis-cusscircuitsinwhichthecurrentvarieswithtime.Finally,wedescribeavarietyofcommonelectricaldevicesandtechniquesformeasuringcurrent,potentialdiffer-ence,resistance,andemf.28.1ELECTROMOTIVEFORCEInSection27.6wefoundthataconstantcurrentcanb

5、emaintainedinaclosedcir-cuitthroughtheuseofasourceofemf,whichisadevice(suchasabatteryorgen-erator)thatproducesanelectricfieldandthusmaycausechargestomovearoundacircuit.Onecanthinkofasourceofemfasa“chargepump.”Whenanelectricpotentialdifferenceexistsbetweentwopoints,thesourcemovescharg

6、es“uphill”fromthelowerpotentialtothehigher.Theemf
describestheworkdoneperunitcharge,andhencetheSIunitofemfisthevolt.ConsiderthecircuitshowninFigure28.1,consistingofabatteryconnectedtoaresistor.Weassumethattheconnectingwireshavenoresistance.Thepositiveterminalofthebatteryisatahigherp

7、otentialthanthenegativeterminal.Ifwene-glecttheinternalresistanceofthebattery,thepotentialdifferenceacrossit(calledtheterminalvoltage)equalsitsemf.However,becausearealbatteryalwayshassomeinternalresistancer,theterminalvoltageisnotequaltotheemfforabatteryinacircuitinwhichthereisacurr

8、ent.Tounderstandwhy