Section1CurrentandVoltageTextNewWordsandExpressionsExercisesEndSection1CurrentandVoltag1Section1CurrentandVoltage

Twovariablesu(t)andi(t)arethemostbasicconceptsinanelectriccircuit,theycharacterizethevariousrelationshipsinanelectriccircuit.

ChargeandCurrentTheconceptofelectricchargeistheunderlyingprincipleforexplainingallelectricalphenomena.Also,themostbasicquantityinanelectriccircuitistheelectriccharge.Chargeisanelectricalpropertyoftheatomicparticlesofwhichmatterconsists,measuredincoulombs(C).Section1CurrentandVoltage2Section1CurrentandVoltageWeknowfromelementaryphysicsthatallmatterismadeoffundamentalbuildingblocksknownasatomsandthateachatomconsistsofelectrons,protons,andneutrons.Wealsoknowthatthechargeeonanelectronisnegativeandequalinmagnitudeto1.60210×1019C,whileaprotoncarriesapositivechargeofthesamemagnitudeastheelectron.Thepresenceofequalnumbersofprotonsandelectronsleavesanatomneutrallycharged.Section1CurrentandVoltage3Section1CurrentandVoltageWeconsidertheflowofelectriccharges.Auniquefeatureofelectricchargeorelectricityisthefactthatitismobile;thatis,itcanbetransferredfromoneplacetoanother,whereitcanbeconvertedtoanotherformofenergy.Whenaconductingwireisconnectedtoabattery(asourceofelectromotiveforce),thechargesarecompelledtomove;positivechargesmoveinonedirectionwhilenegativechargesmoveintheoppositedirection.Thismotionofchargescreateselectriccurrent.Itisconventional

totakethecurrentSection1CurrentandVoltage4Section1CurrentandVoltageflowasthemovementofpositivecharges,thatis,oppositetotheflowofnegativecharges,asFig.l-1illustrates.ThisconventionwasintroducedbyBenjaminFranklin(l706～l790),theAmericanscientistandinventor.Althoughwenowknowthatcurrentinmetallicconductorsisduetonegativelychargedelectrons,wewillfollowtheuniversallyacceptedconventionthatcurrentisthenetflowofpositivecharges.Thus,Electriccurrentisthetimerateofcharge,measuredinamperes(A).

Mathematically,therelationshipamongcurrenti,chargeq,andtimetisSection1CurrentandVoltagefl5Section1CurrentandVoltage

Thechargetransferredbetweentimet0andtisobtainedbyintegratingbothsidesofEq.(1-1).Weobtain

ThewaywedefinecurrentasiinEq.(1-l)suggeststhatcurrentneednotbeaconstant-valuedfunction,chargecanvarywithtimeinseveralwaysthatmayberepresentedbydifferentkindsofmathematicalfunctions.(1-1)(1-2)Section1CurrentandVoltage6Section1CurrentandVoltage

Voltage,Energy,andPowerTomovetheelectroninaconductorinaparticulardirectionrequiressomeworkorenergytransfer.Thisworkisperformedbyanexternalelectromotiveforce(emf),typicallyrepresentedbythebatteryinFig.l-1.Thisemfisalsoknownasvoltageorpotentialdifference.Thevoltageuabbetweentwopointsaandbinanelectriccircuitistheenergy(orwork)neededtomoveaunitchargefromatob;mathematicallySection1CurrentandVoltageV7Section1CurrentandVoltage

wherewisenergyinjoules(J)andqischargeincoulombs(C).Thevoltageuabismeasuredinvolts(V),namedinhonoroftheItalianphysicistAlessandroAntonioVolta(l745～l827),whoinventedthefirstvoltaicbattery.Thus,Voltage(orpotentialdifference)istheenergyrequiredtomoveaunitchargethroughanelement,measuredinvolts(V).(1-3)Section1CurrentandVoltage(8Section1CurrentandVoltageFig.l-2showsthevoltageacrossanelement(representedbyarectangularblock)connectedtopoints

a

and

b.Theplus(+)andminus(-)signsareusedtodefinereferencedirectionorvoltagepolarity.Theuabcanbeinterpretedintwoways:①point

aisatapotentialofuabvoltshigherthanpointb;②thepotentialatpoint

a

withrespecttopointbisuab.ItfollowslogicallythatingeneralFig.1-2Polarityofvoltageuab(1-4)Section1CurrentandVoltage9Section1CurrentandVoltageAlthoughcurrentandvoltagearethetwobasicvariablesinanelectriccircuit,theyarenotsufficientbythemselves.Forpracticalpurposes,weneedtoknowpowerandenergy.Torelatepowerandenergytovoltageandcurrent,werecallfromphysicsthatpoweristhetimerateofexpendingorabsorbingenergy,measuredinwatts(W).

Wewritethisrelationshipas(1-5)Section1CurrentandVoltage10Section1CurrentandVoltageWherepispowerinwatts(W),wisenergyinjoules(J),andtistimeinseconds(s).FromEq.(1-1),Eq.(1-3),andEq.(1-5),itfollowsthat

Becauseuandiaregenerallyfunctionoftime,thepowerpinEq.(1-6)isatime-varyingquantityandiscalledtheinstantaneouspower.Thepowerabsorbedorsuppliedbyanelementistheproductofthevoltageacrosstheelementandthecurrentthroughit.Ifthepowerhasaplussign,powerisbeingdeliveredtoorabsorbedbytheelement.If,(1-6)Section1CurrentandVoltageWh11Section1CurrentandVoltageontheotherhand,thepowerhasaminussign,powerisbeingsuppliedbytheelement.Buthowdoweknowwhenthepowerhasanegativeorapositivesign？Currentdirectionandvoltagepolarityplayamajorroleindeterminingthesignofpower.Itisthereforeimportantthatwepayattentiontotherelationshipbetweencurrentiandvoltage

uinFig.1-3(a).Fig.1-3ReferencepolaritiesforpowerusingthepassivesignconventionSection1CurrentandVoltageon12Section1CurrentandVoltageThevoltagepolarityandcurrentidirectionmustconformwiththoseshowninFig.1-3(a)inorderforthepowertohaveapositivesign.Thisisknownasthepassivesignconvention.Bythepassivesignconvention,currententersthroughthepositivepolarityofthevoltage.Inthiscase,p=uiorui﹥0impliesthattheelementisabsorbingpower.However,ifp=-uiorui﹤0,asinFig.1-3(b),theelementisreleasingorsupplyingpower.Section1CurrentandVoltageTh13Section1CurrentandVoltageInfact,thelawofconservationofenergymustbeobeyedinanyelectriccircuit.Forthisreason,thealgebraicsumofpowerinacircuit,atanyinstantoftime,mustbezeroThisagainconfirmsthefactthatthetotalpowersuppliedtothecircuitmustbalancethetotalpowerabsorbed.FromEq.(l-7),theenergyabsorbedorsuppliedbyanelementfromtimet0totimetis(1-7)(1-8)ReturnSection1CurrentandVoltage14NewWordsandExpressionscurrent n.電流

alternatingcurrent

交流電流

directcurrent

直流電流

currentdensity

電流密度

activecurrent

有功電流

reactivecurrent

無功電流voltage n.電壓

voltagedrop

電壓降落

voltagegain

電壓增益

voltagedivider

分壓器

voltagestabilizer

穩(wěn)壓器NewWordsandExpressionscurre15NewWordsandExpressionsvariable n.變量；a.可變的，可調(diào)的，易變的

complexvariable

復(fù)變量

dependentvariable

因變量

independentvariable

自變量

inputvariable

輸入變量charge n.電荷，充電；v.充電，帶電，起電

chargedistribution

電荷分布

chargeparticle

帶電粒子

testcharge

試驗(yàn)電荷

positivecharge

正電荷

negativecharge

負(fù)電荷NewWordsandExpressionsvaria16NewWordsandExpressionscoulomb n.庫侖（電荷的單位）

coulombmeter

庫侖計(jì)circuit n.電路

circuitdiagram

電路圖

analoguecircuit

模擬電路

shortcircuit

短路

opencircuit

開路

activecircuit

無源電路

passivecircuit

無源電路underlying

a.①基本的，根本的②潛在的，在下（面）的，下伏的NewWordsandExpressionscoulo17NewWordsandExpressionselectron n.電子

magnitude n.大小，尺寸，數(shù)量，數(shù)值electromotive a.電動(dòng)的，起電的

electromotiveforce

電動(dòng)勢(shì)ampere n.安，安培（電流的單位）

amperemeter

安培計(jì)

ampereturn

安匝

voltampere

伏安integrate v.積分，求積分work n.功NewWordsandExpressionselect18NewWordsandExpressionspotentiala.勢(shì)的，位的，電位的；n.勢(shì)（能）,位(能),電勢(shì)(位,壓)

potentialdifference

電位差，電勢(shì)差

earthpotential

地電勢(shì)（位）

potentialenergy

勢(shì)（位）能

referencepotential

參考（基準(zhǔn)）電位rectangular a.矩形的，直角的，正交的joule n.焦?fàn)枺芰?、熱量、功的單位）volt n.伏特（電壓、電位、電勢(shì)的單位）

electronvolt

電子伏特NewWordsandExpressionspoten19NewWordsandExpressionsvoltaica.動(dòng)[流]的，電壓的，電鍍的，伏打(式)的

voltaicbattery

伏打電池convention n.習(xí)慣，慣例，常規(guī)

byconvention

按照慣例referencedirection

參考方向polarity n.極性power n.①功率，效率②動(dòng)力，電力，能力，電源③乘方，冪watt n.瓦特（功率的單位）time-varying a.時(shí)變的NewWordsandExpressionsvolta20NewWordsandExpressionsinstant n.瞬間，瞬時(shí)，即刻，時(shí)，時(shí)刻；a.立刻的，直接的，緊急的，迫切的instantaneousa.瞬時(shí)（作用）的，瞬息的，即刻的

instantaneouspower

瞬時(shí)功率passive a.①無源的②消極的，被動(dòng)的；n.無源

passivenetwork

無源網(wǎng)絡(luò)algebraic a.代數(shù)的ReturnNewWordsandExpressionsinsta21ExercisesI.Choosethebestanswerintotheblank

1.Itisconventionaltotakethecurrentflowasthemovementof

.A.negativecharges B.positivecharges C.anycharge D.protons2.Electriccurrentisthetimerateofcharge,measuredin

.A.watts B.volts C.joules D.amperes

ExercisesI.Choosethebesta22ExercisesI.Choosethebestanswerintotheblank

3.Theenergyrequiredtomoveaunitchargethroughanelementis

.A.current B.power C.voltage D.potential4.Theplus(+)andminus(-)signsinanelectriccircuitdiagramareusedtodefine

.A.voltagepolarity B.currentdirection C.powerflow D.absorbedpowerExercisesI.Choosethebesta23ExercisesI.Choosethebestanswerintotheblank

5.Accordingtothepassivesignconvention,ifthepowerhasaplussign,poweris

bytheelement.A.supplied B.absorbed C.generated D.transferredExercisesI.Choosethebesta24ExercisesII.Answerthefollowingquestionsaccordingtothetext

1.Iscurrentinanyelectriccircuitalwaysaconstant-valuedfunction?Why?2.Howdoescurrentchangewhenthetimerateofchargesisgreater?3.Howtointerprettheuab=-1voltintwoways?4.Whatrelationisbetweenpowerandenergy?5.Whydocurrentdirectionandvoltagepolarityplayamajorroleindeterminingthecharacteristicsofpower?ReturnExercisesII.Answerthefollo25Section1EndSection126Section2CircuitElementsTextNewWordsandExpressionsExercisesEndTranslationStandardSection2CircuitElementsT27Section2CircuitElementsAnelectriccircuitissimplyaninterconnectionoftheelements.Therearetwotypesofelementsfoundinelectriccircuits:passiveelementsandactiveelements.Anactiveelementiscapableofgeneratingenergywhileapassiveelementisnot.Examplesofpassiveelementsareresistors,capacitors,andinductors.Themostimportantactiveelementsarevoltageorcurrentsourcesthatgenerallydeliverpowertothecircuitconnectedtothem.Section2CircuitElementsA28Section2CircuitElements

IndependentsourcesAnidealindependentsourceisanactiveelementthatprovidesaspecifiedvoltageorcurrentthatiscompletelyindependentofothercircuitvariables.Anindependentvoltagesourceisatwo-terminalelement,suchasabatteryoragenerator,whichmaintainsaspecifiedvoltagebetweenitsterminals.Thevoltageiscompletelyindependentofthecurrentthroughtheelement.ThesymbolforavoltagesourcehavinguvoltsacrossitsterminalsisshowninFig.1-4(a).Thepolarityisasshown,Section2CircuitElementsInd29Section2CircuitElementsindicatingthatterminalaisuvoltsaboveterminalb.Thusifu>0,thenterminalaisatahigherpotentialthanterminalb.Theoppositeistrue,ofcourse,ifu<0.InFig.1-4(a),thevoltageumaybetimevarying,oritmaybeconstant,inwhichcasewewouldprobablylabelitU.Anothersymbolthatisoftenusedforaconstantvoltagesource,suchasabatterywithUvoltsacrossitsterminals,isshowninFig.1-4(b).InthecaseofconstantsourcesweshalluseFig.1-4(a)and1-4(b)interchangeably.Section2CircuitElementsindi30Section2CircuitElementsWemightobserveatthispointthatthepolaritymarksonFig.1-4(b)areredundantsincethepolaritycouldbedefinedbythepositionsofthelongerandshorterlines.Fig.1-4Symbolsforindependentvoltagesources(a)usedforconstantortime-varyingvoltage;(b)usedforconstantvoltage(dc).Section2CircuitElementsW31Section2CircuitElementsAnindependentcurrentsourceisatwo-terminalelementthroughwhichaspecifiedcurrentflows.Thecurrentiscompletelyindependentofthevoltageacrosstheelement.ThesymbolforanindependentcurrentsourceisshowninFig.1-5,whereiisthespecifiedcurrent.Thedirectionofthecurrentisindicatedbythearrow.Fig.1-5SymbolsforindependentcurrentsourcesSection2CircuitElementsA32Section2CircuitElementsIndependentsourcesareusuallymeanttodeliverpowertotheexternalcircuitandnottoabsorbit.Thusifuisthevoltageacrossthesourceanditscurrentiisdirectedoutofthepositiveterminal,thenthesourceisdeliveringpower,givenbyp=ui,totheexternalcircuit.Otherwiseitisabsorbingpower.Forexample,inFig.1-6(a)thebatteryisdelivering24Wtotheexternalcircuit.InFig.1-6(b)thebatteryisabsorbing24W,aswouldbethecasewhenitisbeingcharged.Section2CircuitElements33Section2CircuitElementsFig.1-6Symbolsforindependentsources(a)Asourcedeliveringpower;(b)AsourceabsorbingpowerSection2CircuitElementsFig34Section2CircuitElementsDependentsourcesAnidealdependent(orcontrolled)sourceisanactiveelementinwhichthesourcequantityiscontrolledbyanothervoltageorcurrent.Dependentsourcesareusuallydesignatedbydiamond-shapedsymbols,asshowninFig.1-7.Fig.1-7Symbolsfordependentsources(a)Dependentvoltagesource;(b)DependentcurrentsourceSection2CircuitElementsDepe35Section2CircuitElementsSincethecontrolofthedependentsourceisachievedbyavoltageorcurrentofsomeotherelementinthecircuit,andthesourcecanbevoltageorcurrent,itfollowsthattherearefourpossibletypesofdependentsources,namely:（1）Avoltage-controlledvoltagesource(VCVS).（2）Acurrent-controlledvoltagesource(CCVS).（3）Avoltage-controlledcurrentsource(VCCS).（4）Acurrent-controlledcurrentsource(CCCS).Dependentsourcesareusefulinmodelingelementssuchastransistors,operationalamplifiersandintegratedcircuits.Section2CircuitElements36Section2CircuitElementsItshouldbenotedthatanidealvoltagesource(dependentorindependent)willproduceanycurrentrequiredtoensurethattheterminalvoltageisasstated,whereasanidealcurrentsourcewillproducethenecessaryvoltagetoensurethestatedcurrentflow.Thusanidealsourcecouldintheorysupplyaninfiniteamountofenergy.Itshouldalsobenotedthatnotonlydosourcessupplypowertoacircuit,buttheycanabsorbpowerfromacircuittoo.Foravoltagesource,weknowthevoltagebutnotthecurrentsuppliedordrawnbyit.Bythesametoken,weknowthecurrentsuppliedbyacurrentsourcebutnotthevoltageacrossit.ReturnSection2CircuitElements37NewWordsandExpressionsactive a.①有源的，有功的，有效的②活動(dòng)的，主動(dòng)的，積極的③活性的，放射的，激勵(lì)的

activeelement

有源元件resistor n

電阻，電阻器

capacitor n.電容器inductor

n.電感器source n.電源，（光，能，動(dòng)力，信號(hào)，輻射，根，來，起）源

voltagesource

電壓源

currentsource

電流源

idealindependentsource

理想獨(dú)立源NewWordsandExpressionsactiv38NewWordsandExpressionsconstantvoltagesource

恒定電壓源independentsource

獨(dú)立源dependentsource

受控源controlledsource

受控源voltage-controlledvoltagesource電壓控制電壓源current-controlledvoltagesource電流控制電壓源voltage-controlledcurrentsource電壓控制電流源current-controlledcurrentsource電流控制電流源NewWordsandExpressionsconst39NewWordsandExpressionsgenerator n.①發(fā)電機(jī)②（脈沖，信號(hào)，氣體）發(fā)生器，振蕩器，加速器

ACgenerator

交流發(fā)電機(jī)diamond-shaped a.菱形的transistor n.晶體管，半導(dǎo)體管operational a.①運(yùn)算的，計(jì)算的②操作的，工作的，業(yè)務(wù)的，運(yùn)轉(zhuǎn)的amplifier n.放大器integratedcircuit

集成電路NewWordsandExpressionsgener40NewWordsandExpressionstoken

n.①標(biāo)記，象征，記號(hào)②特征，證明

bythesametoken

同理，同樣；另外，還有ReturnNewWordsandExpressionstoken41TranslationStandard

準(zhǔn)確明白

通順嚴(yán)密

簡練全面專業(yè)英語翻譯是對(duì)原文的一種再創(chuàng)作，其標(biāo)準(zhǔn)為TranslationStandard準(zhǔn)確明白通順嚴(yán)密42TranslationStandard

掌握英語語法知識(shí)

具有一定深度的專業(yè)知識(shí)和較為廣博的科學(xué)知識(shí)

有較高的漢語修養(yǎng)為達(dá)到以上翻譯標(biāo)準(zhǔn)，必須做到：

掌握翻譯方法和技巧ReturnTranslationStandard掌握英語語法知識(shí)43ExercisesI.Choosethebestanswerintotheblank

1.Anindependentvoltagesourceisa

,whichmaintainsaspecifiedvoltagebetweenitsterminals.A.one-terminalelement B.two-terminalelementC.three-terminalelement D.four-terminalelement2.Resistorsare

elements.A.passive B.activeC.independentsource D.dependentsourceExercisesI.Choosethebesta44ExercisesI.Choosethebestanswerintotheblank

3.Anidealdependentsourceisan

elementinwhichthesourcequantityiscontrolledbyanothervoltageorcurrent.A.passive B.activeC.independent D.inductive4.Thereare

possibletypesofdependentsources.A.two B.threeC.four D.fiveExercisesI.Choosethebesta45ExercisesI.Choosethebestanswerintotheblank

5.Foravoltagesource,itsterminalvoltageisknownbutits

mustbedeterminedbytheexternalcircuitconnectingwithit.A.electromotiveforce B.currentC.controlcoefficient D.polarityExercisesI.Choosethebesta46ExercisesII.Answerthefollowingquestionsaccordingtothetext

1.Whatdifferenceistherebetweenanindependentsourceandadependentsource?2.Whatelementisanidealindependentsource?3.Isthevoltageofanindependentvoltagesourcedependentofthecurrentthroughtheelement?Howtofindthecurrentthroughit?4.Whatarefourpossibletypesofdependentsources?5.Istheterminalvoltageofindependentvoltagesourcealwaysconstant?ExercisesII.Answerthefollo47ExercisesIII.TranslatethefollowingintoChinese

Allthesimplecircuitelementsthatwillbeconsideredintheworkthatfollowscanbeclassifiedaccordingtotherelationshipofthecurrentthroughtheelementtothevoltageacrosstheelement.Forinstance,ifthevoltageacrosstheelementisdirectlyproportionaltothecurrentthroughit,oru=ki,weshallcalltheelementaresistor.Othertypesofsimplecircuitelementshaveaterminalvoltagewhichisproportionaltothetimederivativeortheintegralwithrespecttotimeofthecurrent.ThereExercisesIII.Translatethef48ExercisesIII.TranslatethefollowingintoChinese

arealsoelementsinwhichthevoltageiscompletelyindependentofthecurrentorthecurrentiscompletelyindependentofthevoltage;thesearetheindependentsources.Furthermore,weshallneedtodefinespecialkindsofsourcesinwhichthesourcevoltageorcurrentdependsuponacurrentorvoltageelsewhereinthecircuit;suchsourceswillbetermeddependentsourcesorcontrolledsources.ReturnExercisesIII.Translatethef49Section2EndSection250Section3Ohm’sLawTextNewWordsandExpressionsExercisesEndProcessofTranslationSection3Ohm’sLawTextNew51Section3Ohm’sLawThecircuitelementusedtomodelthecurrent-resistingbehaviorofamaterialistheresistor.Theresistoristhesimplestpassiveelement.GeorgSimonOhm(1787～1854),aGermanphysicist,iscreditedwithformulatingthecurrent-voltagerelationshipforaresistorbasedonexperimentsperformedin1826.ThisrelationshipisknownasOhm'sLaw.Section3Ohm’sLawThecir52Section3Ohm’sLawOhm'sLawstatesthatthevoltageacrossaresistorisdirectlyproportionaltothecurrentflowingthroughtheresistor.Theconstantofproportionalityistheresistancevalueoftheresistorinohms.ThecircuitsymbolfortheresistorisshowninFig.1-8.Forthecurrentandvoltageshown,Ohm'slawisFig.1-8Circuitsymbolfortheresistor(1-9)Section3Ohm’sLawOhm'sL53Section3Ohm’sLawwhereR≥0istheresistanceinohms.RearrangingEq.(1-9)intotheformR=u(t)/i(t),weseethatlohm=lV/AThesymbolusedtorepresenttheohmisthecapitalGreekomega(Ω).SinceRisconstant,Eq.(1-9)istheequationofastraightline.Forthisreason,theresistoriscalledalinearresistor.

Agraphofu(t)versusi(t)isshowninFig.1-9,whichisalinepassingthroughtheoriginwithaslopeofR.Obviously,astraightlineistheSection3Ohm’sLawwhereR≥054Section3Ohm’sLawonlygraphpossibleforwhichtheratioofu(t)toi(t)isconstantforalli(t).Resistorswhoseresistancesdonotremainconstantfordifferentterminalcurrentsareknownasnonlinearresistors.Forsucharesistor,theresistanceisafunctionofthecurrentflowinginthedevice.Fig.1-9Voltage-currentcharacteristicforalinearresistorSection3Ohm’sLawonlygraph55Section3Ohm’sLawAsimpleexampleofanonlinearresistorisanincandescentlamp.Atypicalvoltage-currentcharacteristicforthisdeviceisshowninFig.1-10,whereweseethatthegraphisnolongerastraightline.SinceRisnotaconstant,theanalysisofacircuitcontainingnonlinearresistorismoredifficult.Fig.1-10Typicalvoltage-currentcharacteristicforanonlinearresistorSection3Ohm’sLawAsimplee56Section3Ohm’sLawInreality,allpracticalresistorsarenonlinearbecausetheelectricalcharacteristicsofallconductorsareaffectedbyenvironmentalfactorssuchastemperature.Manymaterials,however,closelyapproximateanideallinearresistoroveradesiredoperatingregion.Weshallconcentrateonthesetypesofelementsandsimplyrefertothemasresistors.Section3Ohm’sLawInrea57Section3Ohm’sLawSincethevalueofRcanrangefromzerotoinfinity,itisimportantthatweconsiderthetwoextremepossiblevaluesofR.AnelementwithR=0iscalledashortcircuit,asshowninFig.1-11(a).Forashortcircuitu=iR=0（1-10）showingthatthevoltageiszerobutthecurrentcouldbeanything.Inpractice,ashortcircuitisusuallyaconnectingwireassumedtobeaperfectconductor.Thus,ashortcircuitisacircuitelementwithresistanceapproachingzero.Section3Ohm’sLawSincet58Section3Ohm’sLawSimilarly,anelementwithR=∞isknownasanopencircuit,asshowninFig.1-11(b).Foranopencircuit

(1-11)Fig.1-11(a)Shortcircuit(R=0);(b)Opencircuit(R=∞)Section3Ohm’sLawSimilar59Section3Ohm’sLawindicatingthatthecurrentiszerothoughthevoltagecouldbeanything.Thus,anopencircuitisacircuitelementwithresistanceapproachinginfinity.Anotherimportantquantitywhichisusefulincircuitanalysisisknownasconductance,definedby

Theconductanceisameasureofhowwellanelementwillconductelectriccurrent.Theunitofconductanceisthesiemens(S).(1-12)ReturnSection3Ohm’sLawindicating60NewWordsandExpressionsOhm

歐姆（電阻，電抗，阻抗的單位）

Ohm'sLaw

歐姆定律resistance n.①電阻,電阻器（件,裝置）②阻力，阻尼③抵抗，抵制，反對(duì)

resistanceload

電阻(性)負(fù)載

magneticresistance

磁阻

measuringresistance

標(biāo)準(zhǔn)電阻,測(cè)量用電阻rearrange v.重新整理（安排,布置,排列）,調(diào)整NewWordsandExpressionsOhm 61NewWordsandExpressionslinear a.①線性的，一次的②（直）線的，直線型的，線狀的

linearresistor

線性電阻nonlinear a.非線性的，非直線的

nonlinearresistor

非線性電阻incandescent a.白熾（熱）的，熾熱的

incandescentlamp

白熾燈voltage-currentcharacteristic

伏安特性shortcircuit 短路opencircuit 開路NewWordsandExpressionslinea62NewWordsandExpressionsconductance n.①電導(dǎo)，導(dǎo)電性，導(dǎo)納②傳導(dǎo)（性，率，系數(shù)），導(dǎo)率siemens n.西門子（電導(dǎo)單位）ReturnNewWordsandExpressionscondu63ProcessofTranslation

理解階段主要是通過辨明詞義，弄清各種語法成分及其相互關(guān)系，并把前后句子貫串起來理解，形成對(duì)原文的完整印象，真正掌握原文的內(nèi)容和實(shí)質(zhì)。

表達(dá)階段是在理解的基礎(chǔ)上，以忠實(shí)于原意為前提，靈活地運(yùn)用各種翻譯方法和技巧，寫出符合漢語規(guī)范、表達(dá)習(xí)慣以及翻譯標(biāo)準(zhǔn)的譯文。

校核階段是理解與表達(dá)的進(jìn)一步深化，是對(duì)原文內(nèi)容進(jìn)一步核實(shí)，對(duì)譯文語言進(jìn)一步推敲，進(jìn)行必要的潤色和修改，使譯文符合標(biāo)準(zhǔn)規(guī)范。

ReturnProcessofTranslation理解階段主64ExercisesI.Choosethebestanswerintotheblank

1.Thecircuitelementusedtomodelthecurrent-resistingbehaviorofamaterialis

.A.thecapacitor B.theinductor C.theresistor D.thedependentsource2.Ohm'sLawstatesthatthevoltageacrossaresistoris

thecurrentflowingthroughtheresistor.A.equalto B.directlyproportionaltoC.inverselyproportionalto D.differentfromExercisesI.Choosethebesta65ExercisesI.Choosethebestanswerintotheblank

3.Aresistorwhoseresistancesvarywithitscurrentisknownas

.A.alinearresistorB.aconstantresistorC.anonlinearresistorD.atime-varyingresistor4.

isacircuitelementwithresistanceapproach