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1、31FUNDAMENTALSOFCIRCUITSConceptualQuestions31.1.CalculateIV=Δ/.R2V1VIa==1AIb==0.5A2Ω2Ω2V1VIc==2AId==1A1Ω1ΩIIIIcadb>=>.31.2.No.Thisisnotacompletecircuit.Aconnectionfromtheoutermetalcaseofthebulbtothenegativeendofthebatteryisrequiredtomakeacompletecircuit.31.3.Δ=V123V.Thereisnoc
2、urrentthroughtheresistorsothereisnopotentialdifferenceacrosstheresistor.31.4.R21dissipatesmorepower,sincePIR=andthesamecurrentflowsthrougheachresistor.31.5.R22dissipatesmorepower,sincePVR=Δ()/andbothresistorshavethesamepotentialdropVΔbecausetheyareconnectedinparallel.31.6.Calc
3、ulatePVR=Δ()/.222()ΔV()1ΔV1Pa=2RPPb==a28R(2ΔV)2(2ΔV)2PPca==18PPda==2R2R2PPPPcdab>>>.©Copyright2013PearsonEducation,Inc.Allrightsreserved.Thismaterialisprotectedunderallcopyrightlawsastheycurrentlyexist.Noportionofthismaterialmaybereproduced,inanyformorbyanymeans,withoutpermiss
4、ioninwritingfromthepublisher.31-131-2Chapter3131.7.Thetworesistorsareinseries,ascanbeseenbyredrawingthecircuitasfollows:31.8.Increase.RecallΔ=VRRbatε/(+r),whereεistheidealbatteryvoltage.AsRincreases,ΔVbatalsoincreases.Thismakessensesincelesscurrentflowsthroughthecircuit,thusth
5、ereisasmallerpotentialdropinthebatteryduetoitsinternalresistance.Inthecaseofnocurrent(batterydisconnected,RV→∞Δ),.bat=ε31.9.BulbAgetsbrighterandbulbBgoesout.WhentheswitchisclosedallthecurrenttravelsalongthiszeroresistancepathratherthanthroughbulbB.Withlessresistanceinthecircui
6、tthecurrentislarger,sobulbAburnsbrighter.31.10.(a).ABC>=AllcurrentflowingfromthebatterymustgothroughbulbA,thenthecurrentsplitsatthejunctionwithhalfgoingthroughBandhalfthroughC.Withthesameresistanceforeachbulb,thelargercurrentmeansmorebrightness.(b)BulbsBandCgooutbecausenowther
7、eisazeroresistancewirealongwhichallthecurrentwillflow.Nowthetotalresistanceinthecircuithasdecreased,sothecurrentincreasesandbulbAwillburnbrighter.31.11.ApplyingKirchhoff’slooplawaroundtheoutsideedgeofthecircuit,∑Δ=−−Δ=VI11εεRV210⇒Δ=−VI2RThatis,thepotentialdifferenceΔV12between
8、points1and2isthepotentialsuppliedbythebatteryminusthepotentia
