电气工程及其自动化专业英语 Chapter 1 Fundamentals of Electric Circuits.ppt

chapter1fundamentalsofelectriccircuits section1currentandvoltage text newwordsandexpressions exercises end section1currentandvoltage twovariablesu t andi t arethemostbasicconceptsinanelectriccircuit theycharacterizethevariousrelationshipsinanelectriccircuit chargeandcurrenttheconceptofelectricchargeistheunderlyingprincipleforexplainingallelectricalphenomena also themostbasicquantityinanelectriccircuitistheelectriccharge chargeisanelectricalpropertyoftheatomicparticlesofwhichmatterconsists measuredincoulombs c section1currentandvoltage weknowfromelementaryphysicsthatallmatterismadeoffundamentalbuildingblocksknownasatomsandthateachatomconsistsofelectrons protons andneutrons wealsoknowthatthechargeeonanelectronisnegativeandequalinmagnitudeto1 60210 10 19c whileaprotoncarriesapositivechargeofthesamemagnitudeastheelectron thepresenceofequalnumbersofprotonsandelectronsleavesanatomneutrallycharged section1currentandvoltage weconsidertheflowofelectriccharges auniquefeatureofelectricchargeorelectricityisthefactthatitismobile thatis itcanbetransferredfromoneplacetoanother whereitcanbeconvertedtoanotherformofenergy whenaconductingwireisconnectedtoabattery asourceofelectromotiveforce thechargesarecompelledtomove positivechargesmoveinonedirectionwhilenegativechargesmoveintheoppositedirection thismotionofchargescreateselectriccurrent itisconventionaltotakethecurrent section1currentandvoltage flowasthemovementofpositivecharges thatis oppositetotheflowofnegativecharges asfig l 1illustrates thisconventionwasintroducedbybenjaminfranklin l706 l790 theamericanscientistandinventor althoughwenowknowthatcurrentinmetallicconductorsisduetonegativelychargedelectrons wewillfollowtheuniversallyacceptedconventionthatcurrentisthenetflowofpositivecharges thus electriccurrentisthetimerateofcharge measuredinamperes a mathematically therelationshipamongcurrenti chargeq andtimetis section1currentandvoltage thechargetransferredbetweentimet0andtisobtainedbyintegratingbothsidesofeq 1 1 weobtainthewaywedefinecurrentasiineq 1 l suggeststhatcurrentneednotbeaconstant valuedfunction chargecanvarywithtimeinseveralwaysthatmayberepresentedbydifferentkindsofmathematicalfunctions 1 1 1 2 section1currentandvoltage voltage energy andpowertomovetheelectroninaconductorinaparticulardirectionrequiressomeworkorenergytransfer thisworkisperformedbyanexternalelectromotiveforce emf typicallyrepresentedbythebatteryinfig l 1 thisemfisalsoknownasvoltageorpotentialdifference thevoltageuabbetweentwopointsaandbinanelectriccircuitistheenergy orwork neededtomoveaunitchargefromatob mathematically section1currentandvoltage wherewisenergyinjoules j andqischargeincoulombs c thevoltageuabismeasuredinvolts v namedinhonoroftheitalianphysicistalessandroantoniovolta l745 l827 whoinventedthefirstvoltaicbattery thus voltage orpotentialdifference istheenergyrequiredtomoveaunitchargethroughanelement measuredinvolts v 1 3 section1currentandvoltage fig l 2showsthevoltageacrossanelement representedbyarectangularblock connectedtopointsaandb theplus andminus signsareusedtodefinereferencedirectionorvoltagepolarity theuabcanbeinterpretedintwoways pointaisatapotentialofuabvoltshigherthanpointb thepotentialatpointawithrespecttopointbisuab itfollowslogicallythatingeneral fig 1 2polarityofvoltageuab 1 4 section1currentandvoltage althoughcurrentandvoltagearethetwobasicvariablesinanelectriccircuit theyarenotsufficientbythemselves forpracticalpurposes weneedtoknowpowerandenergy torelatepowerandenergytovoltageandcurrent werecallfromphysicsthatpoweristhetimerateofexpendingorabsorbingenergy measuredinwatts w wewritethisrelationshipas 1 5 section1currentandvoltage wherepispowerinwatts w wisenergyinjoules j andtistimeinseconds s fromeq 1 1 eq 1 3 andeq 1 5 itfollowsthatbecauseuandiaregenerallyfunctionoftime thepowerpineq 1 6 isatime varyingquantityandiscalledtheinstantaneouspower thepowerabsorbedorsuppliedbyanelementistheproductofthevoltageacrosstheelementandthecurrentthroughit ifthepowerhasaplussign powerisbeingdeliveredtoorabsorbedbytheelement if 1 6 section1currentandvoltage ontheotherhand thepowerhasaminussign powerisbeingsuppliedbytheelement buthowdoweknowwhenthepowerhasanegativeorapositivesign currentdirectionandvoltagepolarityplayamajorroleindeterminingthesignofpower itisthereforeimportantthatwepayattentiontotherelationshipbetweencurrentiandvoltageuinfig 1 3 a fig 1 3referencepolaritiesforpowerusingthepassivesignconvention section1currentandvoltage thevoltagepolarityandcurrentidirectionmustconformwiththoseshowninfig 1 3 a inorderforthepowertohaveapositivesign thisisknownasthepassivesignconvention bythepassivesignconvention currententersthroughthepositivepolarityofthevoltage inthiscase p uiorui 0impliesthattheelementisabsorbingpower however ifp uiorui 0 asinfig 1 3 b theelementisreleasingorsupplyingpower section1currentandvoltage infact thelawofconservationofenergymustbeobeyedinanyelectriccircuit forthisreason thealgebraicsumofpowerinacircuit atanyinstantoftime mustbezerothisagainconfirmsthefactthatthetotalpowersuppliedtothecircuitmustbalancethetotalpowerabsorbed fromeq l 7 theenergyabsorbedorsuppliedbyanelementfromtimet0totimetis 1 7 1 8 return newwordsandexpressions currentn 电流alternatingcurrent交流电流directcurrent直流电流currentdensity电流密度activecurrent有功电流reactivecurrent无功电流voltagen 电压voltagedrop电压降落voltagegain电压增益voltagedivider分压器voltagestabilizer稳压器 newwordsandexpressions variablen 变量 a 可变的 可调的 易变的complexvariable复变量dependentvariable因变量independentvariable自变量inputvariable输入变量chargen 电荷 充电 v 充电 带电 起电chargedistribution电荷分布chargeparticle带电粒子testcharge试验电荷positivecharge正电荷negativecharge负电荷 newwordsandexpressions coulombn 库仑 电荷的单位 coulombmeter库仑计circuitn 电路circuitdiagram电路图analoguecircuit模拟电路shortcircuit短路opencircuit开路activecircuit无源电路passivecircuit无源电路underlyinga 基本的 根本的 潜在的 在下 面 的 下伏的 newwordsandexpressions electronn 电子magnituden 大小 尺寸 数量 数值electromotivea 电动的 起电的electromotiveforce电动势amperen 安 安培 电流的单位 amperemeter安培计ampereturn安匝voltampere伏安integratev 积分 求积分workn 功 newwordsandexpressions potentiala 势的 位的 电位的 n 势 能 位 能 电势 位 压 potentialdifference电位差 电势差earthpotential地电势 位 potentialenergy势 位 能referencepotential参考 基准 电位rectangulara 矩形的 直角的 正交的joulen 焦尔 能量 热量 功的单位 voltn 伏特 电压 电位 电势的单位 electronvolt电子伏特 newwordsandexpressions voltaica 动 流 的 电压的 电镀的 伏打 式 的voltaicbattery伏打电池conventionn 习惯 惯例 常规byconvention按照惯例referencedirection参考方向polarityn 极性powern 功率 效率 动力 电力 能力 电源 乘方 幂wattn 瓦特 功率的单位 time varyinga 时变的 newwordsandexpressions instantn 瞬间 瞬时 即刻 时 时刻 a 立刻的 直接的 紧急的 迫切的instantaneousa 瞬时 作用 的 瞬息的 即刻的instantaneouspower瞬时功率passivea 无源的 消极的 被动的 n 无源passivenetwork无源网络algebraica 代数的 return exercises i choosethebestanswerintotheblank 1 itisconventionaltotakethecurrentflowasthemovementof a negativechargesb positivechargesc anycharged protons2 electriccurrentisthetimerateofcharge measuredin a wattsb voltsc joulesd amperes exercises i choosethebestanswerintotheblank 3 theenergyrequiredtomoveaunitchargethroughanelementis a currentb powerc voltaged potential4 theplus andminus signsinanelectriccircuitdiagramareusedtodefine a voltagepolarityb currentdirectionc powerflowd absorbedpower exercises i choosethebestanswerintotheblank 5 accordingtothepassivesignconvention ifthepowerhasaplussign powerisbytheelement a suppliedb absorbedc generatedd transferred exercises ii answerthefollowingquestionsaccordingtothetext 1 iscurrentinanyelectriccircuitalwaysaconstant valuedfunction why 2 howdoescurrentchangewhenthetimerateofchargesisgreater 3 howtointerprettheuab 1voltintwoways 4 whatrelationisbetweenpowerandenergy 5 whydocurrentdirectionandvoltagepolarityplayamajorroleindeterminingthecharacteristicsofpower return section1end section2circuitelements text newwordsandexpressions exercises end translationstandard section2circuitelements anelectriccircuitissimplyaninterconnectionoftheelements therearetwotypesofelementsfoundinelectriccircuits passiveelementsandactiveelements anactiveelementiscapableofgeneratingenergywhileapassiveelementisnot examplesofpassiveelementsareresistors capacitors andinductors themostimportantactiveelementsarevoltageorcurrentsourcesthatgenerallydeliverpowertothecircuitconnectedtothem section2circuitelements independentsourcesanidealindependentsourceisanactiveelementthatprovidesaspecifiedvoltageorcurrentthatiscompletelyindependentofothercircuitvariables anindependentvoltagesourceisatwo terminalelement suchasabatteryoragenerator whichmaintainsaspecifiedvoltagebetweenitsterminals thevoltageiscompletelyindependentofthecurrentthroughtheelement thesymbolforavoltagesourcehavinguvoltsacrossitsterminalsisshowninfig 1 4 a thepolarityisasshown section2circuitelements indicatingthatterminalaisuvoltsaboveterminalb 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 section2circuitelements wemightobserveatthispointthatthepolaritymarksonfig 1 4 b areredundantsincethepolaritycouldbedefinedbythepositionsofthelongerandshorterlines fig 1 4symbolsforindependentvoltagesources a usedforconstantortime varyingvoltage b usedforconstantvoltage dc section2circuitelements anindependentcurrentsourceisatwo terminalelementthroughwhichaspecifiedcurrentflows thecurrentiscompletelyindependentofthevoltageacrosstheelement thesymbolforanindependentcurrentsourceisshowninfig 1 5 whereiisthespecifiedcurrent thedirectionofthecurrentisindicatedbythearrow fig 1 5symbolsforindependentcurrentsources section2circuitelements independentsourcesareusuallymeanttodeliverpowertotheexternalcircuitandnottoabsorbit thusifuisthevoltageacrossthesourceanditscurrentiisdirectedoutofthepositiveterminal thenthesourceisdeliveringpower givenbyp ui totheexternalcircuit otherwiseitisabsorbingpower forexample infig 1 6 a thebatteryisdelivering24wtotheexternalcircuit infig 1 6 b thebatteryisabsorbing24w aswouldbethecasewhenitisbeingcharged section2circuitelements fig 1 6symbolsforindependentsources a asourcedeliveringpower b asourceabsorbingpower section2circuitelements dependentsourcesanidealdependent orcontrolled sourceisanactiveelementinwhichthesourcequantityiscontrolledbyanothervoltageorcurrent dependentsourcesareusuallydesignatedbydiamond shapedsymbols asshowninfig 1 7 fig 1 7symbolsfordependentsources a dependentvoltagesource b dependentcurrentsource section2circuitelements sincethecontrolofthedependentsourceisachievedbyavoltageorcurrentofsomeotherelementinthecircuit andthesourcecanbevoltageorcurrent itfollowsthattherearefourpossibletypesofdependentsources namely 1 avoltage controlledvoltagesource vcvs 2 acurrent controlledvoltagesource ccvs 3 avoltage controlledcurrentsource vccs 4 acurrent controlledcurrentsource cccs dependentsourcesareusefulinmodelingelementssuchastransistors operationalamplifiersandintegratedcircuits section2circuitelements itshouldbenotedthatanidealvoltagesource dependentorindependent willproduceanycurrentrequiredtoensurethattheterminalvoltageisasstated whereasanidealcurrentsourcewillproducethenecessaryvoltagetoensurethestatedcurrentflow thusanidealsourcecouldintheorysupplyaninfiniteamountofenergy itshouldalsobenotedthatnotonlydosourcessupplypowertoacircuit buttheycanabsorbpowerfromacircuittoo foravoltagesource weknowthevoltagebutnotthecurrentsuppliedordrawnbyit bythesametoken weknowthecurrentsuppliedbyacurrentsourcebutnotthevoltageacrossit return newwordsandexpressions activea 有源的 有功的 有效的 活动的 主动的 积极的 活性的 放射的 激励的activeelement有源元件resistorn 电阻 电阻器capacitorn 电容器inductorn 电感器sourcen 电源 光 能 动力 信号 辐射 根 来 起 源voltagesource电压源currentsource电流源idealindependentsource理想独立源 newwordsandexpressions constantvoltagesource恒定电压源independentsource独立源dependentsource受控源controlledsource受控源voltage controlledvoltagesource电压控制电压源current controlledvoltagesource电流控制电压源voltage controlledcurrentsource电压控制电流源current controlledcurrentsource电流控制电流源 newwordsandexpressions generatorn 发电机 脉冲 信号 气体 发生器 振荡器 加速器acgenerator交流发电机diamond shapeda 菱形的transistorn 晶体管 半导体管operationala 运算的 计算的 操作的 工作的 业务的 运转的amplifiern 放大器integratedcircuit集成电路 newwordsandexpressions tokenn 标记 象征 记号 特征 证明bythesametoken同理 同样 另外 还有 return translationstandard 准确明白 通顺严密 简练全面 专业英语翻译是对原文的一种再创作 其标准为 translationstandard 掌握英语语法知识 具有一定深度的专业知识和较为广博的科学知识 有较高的汉语修养 为达到以上翻译标准 必须做到 掌握翻译方法和技巧 return exercises i choosethebestanswerintotheblank 1 anindependentvoltagesourceisa whichmaintainsaspecifiedvoltagebetweenitsterminals a one terminalelementb two terminalelementc three terminalelementd four terminalelement2 resistorsareelements a passiveb activec independentsourced dependentsource exercises i choosethebestanswerintotheblank 3 anidealdependentsourceisanelementinwhichthesourcequantityiscontrolledbyanothervoltageorcurrent a passiveb activec independentd inductive4 therearepossibletypesofdependentsources a twob threec fourd five exercises i choosethebestanswerintotheblank 5 foravoltagesource itsterminalvoltageisknownbutitsmustbedeterminedbytheexternalcircuitconnectingwithit a electromotiveforceb currentc controlcoefficientd polarity exercises ii answerthefollowingquestionsaccordingtothetext 1 whatdifferenceistherebetweenanindependentsourceandadependentsource 2 whatelementisanidealindependentsource 3 isthevoltageofanindependentvoltagesourcedependentofthecurrentthroughtheelement howtofindthecurrentthroughit 4 whatarefourpossibletypesofdependentsources 5 istheterminalvoltageofindependentvoltagesourcealwaysconstant exercises iii translatethefollowingintochinese allthesimplecircuitelementsthatwillbeconsideredintheworkthatfollowscanbeclassifiedaccordingtotherelationshipofthecurrentthroughtheelementtothevoltageacrosstheelement forinstance ifthevoltageacrosstheelementisdirectlyproportionaltothecurrentthroughit oru ki weshallcalltheelementaresistor othertypesofsimplecircuitelementshaveaterminalvoltagewhichisproportionaltothetimederivativeortheintegralwithrespecttotimeofthecurrent there exercises iii translatethefollowingintochinese arealsoelementsinwhichthevoltageiscompletelyindependentofthecurrentorthecurrentiscompletelyindependentofthevoltage thesearetheindependentsources furthermore weshallneedtodefinespecialkindsofsourcesinwhichthesourcevoltageorcurrentdependsuponacurrentorvoltageelsewhereinthecircuit suchsourceswillbetermeddependentsourcesorcontrolledsources return section2end section3ohm slaw text newwordsandexpressions exercises end processoftranslation section3ohm slaw thecircuitelementusedtomodelthecurrent resistingbehaviorofamaterialistheresistor theresistoristhesimplestpassiveelement georgsimonohm 1787 1854 agermanphysicist iscreditedwithformulatingthecurrent voltagerelationshipforaresistorbasedonexperimentsperformedin1826 thisrelationshipisknownasohm slaw section3ohm slaw ohm slawstatesthatthevoltageacrossaresistorisdirectlyproportionaltothecurrentflowingthroughtheresistor theconstantofproportionalityistheresistancevalueoftheresistorinohms thecircuitsymbolfortheresistorisshowninfig 1 8 forthecurrentandvoltageshown ohm slawis fig 1 8circuitsymbolfortheresistor 1 9 section3ohm slaw wherer 0istheresistanceinohms rearrangingeq 1 9 intotheformr u t i t weseethatlohm lv athesymbolusedtorepresenttheohmisthecapitalgreekomega sincerisconstant eq 1 9 istheequationofastraightline forthisreason theresistoriscalledalinearresistor agraphofu t versusi t isshowninfig 1 9 whichisalinepassingthroughtheoriginwithaslopeofr obviously astraightlineisthe section3ohm slaw onlygraphpossibleforwhichtheratioofu t toi t isconstantforalli t resistorswhoseresistancesdonotremainconstantfordifferentterminalcurrentsareknownasnonlinearresistors forsucharesistor theresistanceisafunctionofthecurrentflowinginthedevice fig 1 9voltage currentcharacteristicforalinearresistor section3ohm slaw asimpleexampleofanonlinearresistorisanincandescentlamp atypicalvoltage currentcharacteristicforthisdeviceisshowninfig 1 10 whereweseethatthegraphisnolongerastraightline sincerisnotaconstant theanalysisofacircuitcontainingnonlinearresistorismoredifficult fig 1 10typicalvoltage currentcharacteristicforanonlinearresistor section3ohm slaw inreality allpracticalresistorsarenonlinearbecausetheelectricalcharacteristicsofallconductorsareaffectedbyenvironmentalfactorssuchastemperature manymaterials however closelyapproximateanideallinearresistoroveradesiredoperatingregion weshallconcentrateonthesetypesofelementsandsimplyrefertothemasresistors section3ohm slaw sincethevalueofrcanrangefromzerotoinfinity itisimportantthatweconsiderthetwoextremepossiblevaluesofr anelementwithr 0iscalledashortcircuit asshowninfig 1 11 a forashortcircuitu ir 0 1 10 showingthatthevoltageiszerobutthecurrentcouldbeanything inpractice ashortcircuitisusuallyaconnectingwireassumedtobeaperfectconductor thus ashortcircuitisacircuitelementwithresistanceapproachingzero section3ohm slaw similarly anelementwithr isknownasanopencircuit asshowninfig 1 11 b foranopencircuit 1 11 fig 1 11 a shortcircuit r 0 b opencircuit r section3ohm slaw indicatingthatthecurrentiszerothoughthevoltagecouldbeanything thus anopencircuitisacircuitelementwithresistanceapproachinginfinity anotherimportantquantitywhichisusefulincircuitanalysisisknownasconductance definedbytheconductanceisameasureofhowwellanelementwillconductelectriccurrent theunitofconductanceisthesiemens s 1 12 return newwordsandexpressions ohm欧姆 电阻 电抗 阻抗的单位 ohm slaw欧姆定律resistancen 电阻 电阻器 件 装置 阻力 阻尼 抵抗 抵制 反对resistanceload电阻 性 负载magneticresistance磁阻measuringresistance标准电阻 测量用电阻rearrangev 重新整理 安排 布置 排列 调整 newwordsandexpressions lineara 线性的 一次的 直 线的 直线型的 线状的linearresistor线性电阻nonlineara 非线性的 非直线的nonlinearresistor非线性电阻incandescenta 白炽 热 的 炽热的incandescentlamp白炽灯voltage currentcharacteristic伏安特性shortcircuit短路opencircuit开路 newwordsandexpressions conductancen 电导 导电性 导纳 传导 性 率 系数 导率siemensn 西门子 电导单位 return processoftranslation 理解阶段主要是通过辨明词义 弄清各种语法成分及其相互关系 并把前后句子贯串起来理解 形成对原文的完整印象 真正掌握原文的内容和实质 表达阶段是在理解的基础上 以忠实于原意为前提 灵活地运用各种翻译方法和技巧 写出符合汉语规范