Electrical Circuits Capacitance in AC Circuits

Unit20:CapacitanceinACCircuits Indicatewhetherthestatementistrueorfalse. 1.WhenacapacitorisconnectedtoanACcircuit,currentappearstoflowthroughthecapacitor. a.True b.False 2.Thereistruepowerproducedinapurecapacitivecircuit. a.True b.False 3.Thecountervoltageinacapacitivereactanceissimilartothecountervoltageproducedbyaninductor. a.True b.False 4.Thepowerrequiredtochargethecapacitorinapurecapacitivecircuitisreturnedtothecircuitwhenthe capacitordischarges. a.True b.False Indicatetheanswerchoicethatbestcompletesthestatementoranswersthequestion. 5.Howisfrequencymeasuredwhencalculatingforcapacitivereactance? a.ampere b.picofarad c.hertz d.farad 6.Thepowerinacapacitorisreactivepower.Whatistheunitforreactivepower? a.W b.VA c.P d.VAR 7.A1μFcapacitorhas2,652Ωofreactanceat60-Hz.Whatisthereactancevalueat400-Hz? a.397.88Ω b.568.72Ω c.639.79Ω d.768.33Ω 8.Whatistheunitforcapacitivereactance? a.ohm b.farad c.henry d.coulomb Page 1 Unit20:CapacitanceinACCircuits 9.Thevoltageratingofacapacitor_____. a.canbeexceededaslongasthetimeisunderonehour b.shouldneverbeexceeded c.isonlyasuggestedmaximum d.isaminimumworkingvoltage 10.Whatisthereactanceofa10pFcapacitorwhentheappliedfrequencyis30-Hz? a.200.36Ω b.325.76Ω c.530.52Ω d.612.83Ω 11.Whenacapacitorisconnectedtoa(n)_____circuit,currentappearstoflowthroughthecapacitor. a.DC b.AC 12.Twocapacitors,a20μFanda30μF,areconnectedinparalleltoa400-Hzsource.Whatisthetotalcapacitive reactance? a.7.96Ω b.33.16Ω c.42.04Ω d.53.05Ω 13.Threecapacitors,a12μF,a20μF,anda30μF,areconnectedinseriestoa400-Hzsource.Whatisthetotal XC? a.36.42Ω b.42.78Ω c.52.09Ω d.66.32Ω 14.Inacircuitcontainingacapacitor,theimpressedvoltageis_____withtheappliedvoltage. a.180°outofphase b.90°outofphase c.inphase d.270°outofphase 15.Twocapacitors,a20μFanda30μF,areconnectedinseriestoa60-Hzsource.Whatisthetotalcapacitive reactance? a.117.96Ω b.221.04Ω c.253.05Ω d.333.16Ω Page 2 Unit20:CapacitanceinACCircuits 16.Whatisprovidedbytheelectrostaticcharge? a.truevoltage b.apparentvoltage c.impressedvoltage d.appliedvoltage 17.Whichistheformulaforfindingcapacitance? a. b. c. d. 18.Thecapacitivereactanceofacapacitoris_____proportionaltofrequency. a.directly b.inversely 19.Ifacapacitoris____________,thedielectricwillappeartobeamuchlowerresistanceandtheQratingwill decrease. a.lagging b.leading c.leaking d.charging 20.Countervoltagepresentedbyacapacitoriscalled_____. a.capacitance b.inductance c.capacitivereactance d.inductivereactance Page 3 Unit20:CapacitanceinACCircuits 21.Whatisthesymbolforcapacitivereactance? a.C b.XC c.L d.XL 22.Ifa(n)____________wereplacedinanACcircuit,itwouldindicateacontinuousflowofcurrent,givingthe appearancethatcurrentisflowingthroughthecapacitor. a.ammeter b.ohmmeter c.voltmeter d.wattmeter 23.Inapurecapacitivecircuit,thecurrent_____theappliedvoltageby_____. a.leads;180° b.lags;180° c.leads;90° d.lags;90° 24.A35μFcapacitorisconnectedtoa60-Hz,120Vsupply.WhatistheXCofthecapacitor? a.75.79Ω b.80.33Ω c.83.2Ω d.93.43Ω 25.Whatisthereactanceofa25μFcapacitorwhentheappliedfrequencyis400-Hz? a.10.61Ω b.11.59Ω c.15.92Ω d.16.12Ω 26.WhenacapacitorisconnectedtoanACcircuit,the__________chargesoneplateofthecapacitorpositive andtheotherplatenegative. a.DCgenerator b.ACgenerator c.capacitor d.reactor Page 4 Unit20:CapacitanceinACCircuits 27.Threecapacitors,a12μF,a20μF,anda30μF,areconnectedinparalleltoa60-Hzsource.Whatisthetotal XC? a.6.42Ω b.42.78Ω c.442.09Ω d.566.32Ω 28.Twocapacitors,a20μFanda30μF,areconnectedinseriestoa400-Hzsource.Whatisthetotalcapacitive reactance? a.7.96Ω b.33.16Ω c.42.04Ω d.53.05Ω 29.Threecapacitors,a12μF,a20μF,anda30μF,areconnectedinseriestoa60-Hzsource.WhatisthetotalXC? a.226.42Ω b.342.78Ω c.442.09Ω d.566.32Ω 30.Acapacitorisconnectedtoa240Vsupply.Anammeterindicates3A.Whatisthecapacitivereactanceofthe capacitor? a.23Ω b.30Ω c.71Ω d.80Ω 31.Twocapacitors,a20μFanda30μF,areconnectedinparalleltoa60-Hzsource.Whatisthetotalcapacitive reactance? a.7.96Ω b.23.16Ω c.42.04Ω d.53.05Ω 32.Threecapacitors,a12μF,a20μF,anda30μF,areconnectedinparalleltoa400-Hzsource.Whatisthetotal XC? a.6.42Ω b.42.78Ω c.44.09Ω d.56.32Ω Copyright Cengage Learning. 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Page 5 Unit20:CapacitanceinACCircuits 33.Aslongasthe____________continuestoincrease,decrease,andchangepolaritywhenacapacitoris connectedtoanACcircuit,currentflowsfromoneplateofthecapacitortotheother. a.truepower b.power c.wattage d.voltage 34.Duringtheperiodoftimethatvoltageandcurrenthavethesamepolarityinapurecapacitivecircuit,whereis energybeingstored? a.inthecircuit b.inthecapacitor c.inthecurrent d.intheresistor 35.Howiscapacitancemeasuredwhencalculatingforcapacitivereactance? a.ampere b.picofarad c.hertz d.farad 36.Whatisenergystoredasinapurecapacitivecircuit? a.power b.truepower c.voltage d.electrostaticfield 37.Whichvalueinthequalityofacapacitorformulaisgenerallyveryhighbecauseitistheequivalentresistanceof thedielectricbetweentheplatesofthecapacitor? a.Q b.R c.XC d.mega(M) 38.Thevoltageratingofelectrolyticorpolarizedcapacitorsisalwaysgiveninwhattypeofvolts? a.working b.peak c.AC d.DC Page 6 Unit20:CapacitanceinACCircuits Indicatewhetherthestatementistrueorfalse. 39.Becausethecurrentflowinapurecapacitivecircuitleadstheappliedvoltageby90°,thevoltageandcurrent havethesamepolarityforhalfthetimeduringonecycleandhaveoppositepolaritiestheotherhalfofthetime. a.True b.False Page 7 Unit20:CapacitanceinACCircuits AnswerKey 1.True 2.False 3.True 4.True 5.c 6.d 7.a 8.a 9.b 10.c 11.b 12.a 13.d 14.a 15.b 16.c 17.b 18.b 19.c 20.c 21.b 22.a 23.c 24.a 25.c 26.b Page 8 Unit20:CapacitanceinACCircuits 27.c 28.b 29.c 30.d 31.d 32.a 33.d 34.b 35.d 36.d 37.b 38.d 39.True Page 9