Alternating-Current Circuits

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1、CHAPTER31Alternating-CurrentCircuitsNote:Unlessotherwiseindicated,thesymbolsI,V,E,andPdenotethermsvaluesofI,V,andEandtheaveragepower.21*∙A200-turncoilhasanareaof4cmandrotatesinamagneticfieldof0.5T.(a)Whatfrequencywillgenerateamaximumemfof10V?(b)Ifthecoilro

2、tatesat60Hz,whatisthemaximumemf?–1(a)E=NBAwcoswt(seeProblem30-8-5)w=Emax/NBA=250s;f=w/2p=39.8Hz(b)Emax=NBAw=2pNBAfEmax=15.1V2∙InwhatmagneticfieldmustthecoilofProblem1berotatingtogenerateamaximumemfof10Vat60Hz?UseEqu.31–4;solveforBB=0.332T3∙A2-cmby1.5-cmrec

3、tangularcoilhas300turnsandrotatesinamagneticfieldof4000G.(a)Whatisthemaximumemfgeneratedwhenthecoilrotatesat60Hz?(b)Whatmustitsfrequencybetogenerateamaximumemfof110V?(a)UseEqu.31-4Emax=13.6V(b)UseEqu.31-4;solveforf=w/2pf=486Hz4∙ThecoilofProblem3rotatesat60

4、HzinamagneticfieldB.WhatvalueofBwillgenerateamaximumemfof24V?UseEqu.31-4;solveforBB=0.707T5*∙AsthefrequencyinthesimpleaccircuitinFigure31-26increases,thermscurrentthroughtheresistor(a)increases.(b)doesnotchange.(c)mayincreaseordecreasedependingonthemagnitu

5、deoftheoriginalfrequency.(d)mayincreaseordecreasedependingonthemagnitudeoftheresistance.(e)decreases.(b)6∙Ifthermsvoltageinanaccircuitisdoubled,thepeakvoltageis(a)increasedbyafactorof2.(b)decreasedbyafactorof2.(c)increasedbyafactorof2.(d)decreasedbyafactor

6、of2.(e)notchanged.(a)7∙A100-Wlightbulbispluggedintoastandard120-V(rms)outlet.Find(a)Irms,(b)Imax,and(c)themaximumpower.(a)UseEqu.31-14Irms=0.833A(b)UseEqu.31-12Imax=1.18AChapter31Alternating-CurrentCircuits(c)Pmax=ImaxEmax=2IrmsErms=2PavPmax=200W8∙A3-Wresi

7、storisplacedacrossageneratorhavingafrequencyof60Hzandamaximumemfof12.0V.(a)Whatistheangularfrequencywofthecurrent?(b)FindImaxandIrms.Whatis(c)themaximumpowerintotheresistor,(d)theminimumpower,and(e)theaveragepower?(a)w=2pfw=377rad/s(b)UseEqus.31-8and31-12I

8、max=4A;Irms=2.83A2(c)Pmax=ImaxRPmax=48W2(d)Pmin=(½I½min)RPmin=0(e)Pav=1/2PmaxPav=24W9*∙Acircuitbreakerisratedforacurrentof15Armsatavoltageof120Vrms.(a)WhatisthelargestvalueofImaxthatthebreakercancarry?(b)What