电气专业专用英语课件

Impedancen.阻抗 resistancen.阻力，电阻，阻抗

resistn.阻抗

resistor(er)n.电阻器

resistiven.电阻性的

resistivityn.电阻率reactancen.电抗

componentreactance电抗分量

capacitivereactance容抗

inductivereactance感抗WhatIsResistance?Impedancen.阻抗 resistancen.阻力，电阻，阻抗

resistn.阻抗

resistor(er)n.电阻器

resistiven.电阻性的

resistivityn.电阻率reactancen.电抗

componentreactance电抗分量

capacitivereactance容抗

inductivereactance感抗insulatorn.绝缘体

insulatedconductor绝缘线conductorn.导体Semiconductorn.半导体ohmn.欧姆voltagen.电压，伏特数Currentn.电流amperen.安培wattagen.瓦特数ratingn.额定seriesn.连续，串联paralleln.平行线，并联capabilityn.能力，性能，容量materialn.材料，原料formulan.公式，规则precisionn.精确accuracyn.精确性confusionn.混乱between…and在……之间ontheotherhand另一方面takeadvantageof利用closein包围,封闭,渐短Freeelectron自由电子thenumberof…的数目displacementequalsonehalftimesaccelerationandtimesquared.

displacementequalsonehalfmultipliedbyaccelerationandtimesquared.

displacementequalsaccelerationtimestimesquaredovertwo.

displacementequalsaccelerationmultipliedbytimesquareddividedbytwo.

displacementequalshalfoftheaccelerationtimestimesquared1.Logic逻辑∃thereexist∀forallp⇒qpimpliesq/ifp,thenqp⇔qpifandonlyifq/pisequivalenttoq/pandqareequivalent2.Sets集合x∈AxbelongstoA/xisanelement(oramember)ofAx∉AxdoesnotbelongtoA/xisnotanelement(oramember)ofAA⊂BAiscontainedinB/AisasubsetofBA⊃BAcontainsB/BisasubsetofAA∩BAcapB/AmeetB/AintersectionBA∪BAcupB/AjoinB/AunionBA/BAminusB/thedifferencebetweenAandBA×BAcrossB/thecartesianproductofAandB3.Realnumbersx+1:xplusone x-1:xminusonex±1:xplusorminusone

xy:xy/xmultipliedbyy(x-y)(x+y):xminusy,xplusyx/y:xovery=:theequalssignx=5:xequals5/xisequalto5x≠5:x(is)notequalto5x≡y:xisequivalentto(oridenticalwith)yx>y:xisgreaterthanyx≥y:xisgreaterthanorequaltoyx<y:xislessthanyx≤y:xislessthanorequaltoy0<x<1:zeroislessthanxislessthan10≤x≤1:zeroislessthanorequaltoxislessthanorequalto13.Realnumbers|x|modx/modulusxx2xsquared/x(raised)tothepower2x3xcubed x4xtothefourth/xtothepowerfourxnxtothenth/xtothepowernx−nxtothe(power)minus(square)rootx/thesquarerootofxcuberoot(of)xfourthroot(of)xnthroot(of)x(x+y)2xplusyallsquared(x/y)2xoveryallsquared4.Functionsf(x)fx/fofx/thefunctionfofxf:S→TafunctionffromStoTx→yxmapstoy/xissent(ormapped)toyf'(x)fprimex/fdashx/the(first)derivativeoffwithrespecttoxf''(x)fdouble-primex/fdouble-dashx/thesecondderivativeoffwithrespecttoxf'''(x)triple-primex/ftriple-dashx/thethirdderivativeoffwithrespecttoxf(4)(x)ffourx/thefourthderivativeoffwithrespecttox

4.Functionsthepartial(derivative)offwithrespecttox1

thesecondpartial(derivative)offwithrespecttox1

theintegralfromzerotoinfinitythelimitasxapproacheszerothelimitasxapproacheszerofromabovethelimitasxapproacheszerofrombelowlogytothebasee/logtothebaseeofy/naturallog(of)ylogytothebasee/logtothebaseeofy/naturallog(of)y5.Linearalgebra线性代数‖x‖thenorm(ormodulus)ofxOA/vectorOAOA/thelengthofthesegmentOAATAtranspose/thetransposeofAA−1Ainverse/theinverseofAthesoundsfxmaybeinterpretedasanyof:fx,f(x),fx,FX,,.Thedifferenceisusuallymadeclearbythecontext;itisonlywhenconfusionmayoccur,orwherehe/shewishestoemphasisethepoint,thatthemathematicianwillusethelongerforms:fmultipliedbyx,thefunctionfofx,fsubscriptx,lineFX,thelengthofthesegmentFX,vectorFX.Whatisresistance?什么是电阻Weknowthatcertainmaterialssuchascopperhavemanyfreeelectrons.我们知道像铜这类物质中有许多自由电子。Othermaterialshavefewerfreeelectronsandsubstancessuchasglass,另外一些物质只有很少的自由电子。还有一些物质如玻璃、

rubber,micahavepracticallynofreeelectronmovement橡皮及云母实际上没有可以自由移动的电子，

thereforemakinggoodinsulators.因此，可以做成很好的绝缘体。Betweentheextremesofgoodconductorssuchassilverandcopper在好的导体如银和铜两端之间layotherconductorsofreducedconductingability,

放置别的减少导通能力的导体，they"resist"theflowofelectronshencethetermresistance.它们阻碍对“电子流”因此叫做电阻。Thespecificresistanceofaconductoristhenumberofohms.

用欧姆数来精确描述导体电阻值的大小。SomeexamplesonthatbasisareSilver=9.75ohms,Copper=10.55ohms,Nickel=53.0ohmsandNichrome=660ohms基于这一基础上的一些例子是：银=9.75欧姆，铜=10.55欧姆，镍=53.0欧姆，镍铬合金=660欧姆。Fromthisinformationwecandeducethatforavoltageappliedtoapieceofnichromewire,从这个信息中我们可以推导出当一个电压加在一段镍铬线上时，

onlyaround10.55/660=0.016oftheamountofcurrentwillflowasopposedtothecurrentflowinginthesamesizecopperwire.流过它的电流只是相当于相同的电压加在相同尺寸铜线上的10.55/660=0.0016倍。Theunitofresistanceistheohm电阻的单位是欧姆，and1ohmisconsideredtheresistanceofroundcopperwire,0.001"diameter,0.88"(22.35mm)longat32degF(0degC).1欧姆相当于直径为0.001英寸、长度为0.88英寸(22.35mm)的圆铜线在32度（华氏）或0度（摄氏）时的电阻。Resistanceinseriesandparallel1.串联和并联电阻Itfollowsiftwosuchpiecesofwirewereconnectedendtoend(inseries)如果两根电线头尾相连接（串联），thentheresistancewouldbedoubled,那么电阻就为原来的两倍；ontheotherhandiftheywereplacedsidebyside(inparallel)

另一方面，如果它们的两端相连（并联），thentheresistancewouldbehalved!那么电阻是一根线的一半。Thisisamostimportantlessonaboutresistance.这是关于电阻的重要理论。

ResistorsinseriesaddtogetherasR1+R2+R3+电阻串联时电阻是以R1+R2+R3……的方式增加；Whileresistorsinparallelreduceby1/(1/R1+1/R2+1/R3+)并联时电阻是以1/（1/R1+1/R2+1/R3+……）的方式减小。Considerthreeresistorsof10,22,and47ohmsrespectively.

例如三个阻值分别为10欧姆、20欧姆和47欧姆的电阻。Addedinseriesweget10+22+47=79ohms.

以串联方式连接得到的电阻是10+22+47=79欧姆；

Whileinparallelwewouldget1/(1/10+1/22+1/47)=5.997ohms.以并联方式连接得到的电阻是1/（1/10+1/22+1/47）=5.997欧姆。ResistanceandPower2．电阻和功率Nextweneedtoconsiderthepowerhandlingcapabilityofourresistors.

下面讨论电阻器的功率性能。Resistorswhicharedeliberatelydesignedtohandleandradiatelargeamountsofpowerareelectriccooktops,ovens,radiators,electricjugsandtoasters.

在电炉灶面、烤箱、电暖炉、电水壶和烘箱上设置电阻器，其目的是利用它处理和消耗很大的功率。Theseareallmadetotakeadvantageofpowerhandlingcapabilitiesofcertainmaterials.这些电器都是根据某些物质的这一功率性能而制成。Fromohm’slawwelearntthatP=I*I*Rthatis,从欧姆定理我们知道：P=I*I*R，powerequalsthecurrentsquaredtimestheresistance.即功率等于电流的平方乘以电阻。Considerourexampleaboveofthethreeresistorsinseriesprovidingatotalresistanceof79ohms.

上面例子中，三个电阻器串联得到79欧姆电阻器，

Iftheseresistorswereplacedacrossa24voltpowersupply如果在它们上面加上24伏特电压，thentheamountofcurrentflowing,fromohmslaw,isI=E/R=24/79=0.304amperes.从欧姆定理就可知流过的总电流：I=V/R=24/79=0.304安培。Usinganyofourpowerformulaswedeterminethat0.304amperesflowingthroughour79ohmresistancedissipatesacombined7.3wattsofpower!用任何功率公式我们都可以确定0.304安培的电流流过79欧姆的电阻总共要消耗7.3瓦特的能量！Worse,becauseourresistorsareofunequalvaluethepowerdistributionwillbeunequalwiththegreaterdissipationinthelargestresistor.而且，当电阻器上的电阻大小不等时，电阻越大，消耗的能量也就越多。Itfollowsasafundamentalruleinusingresistorsinelectroniccircuits电路中消耗能量的电阻器的使用有其基本规律，thattheresistormustbeabletocomfortablyhandlethepoweritwilldissipate.即电阻必须能够充裕地处理它将要消耗的功率

Aruleofthumbistouseawattageratingofatleasttwicetheexpecteddissipation.即用到的电阻的额定功率至少是有效使用功率的两倍，这是一个很重要的经验规律。Commonresistorsinuseinelectronicstodaycomeinpowerratingsof0.25W,0.5W,1Wand5W.

目前通常使用的电阻器是0.25W，0.5W，1W和5W。Otherspecialtypesareavailabletoorder.别的特殊类型可以定做。Becauseofprecisionmanufacturingprocessesitispossibletoobtainresistorsinthelowerwattageratingswhicharequitecloseintoleranceoftheirdesignatedvalues.由于制造精密，低功率的电阻器误差有可能在设计允许的范围内，

Typicalofthistypearethe.25Wrangewhichexhibitatoleranceofplus/minus2%ofthevalue.这一类型的典型是0.25瓦的电阻器，其实际值与设计值误差在±2%。ResistorscomeinarangeofvaluesbutthetwomostcommonaretheE12andE24series.电阻器有不同的取值范围，但最常用的两种是E12和E24系列。

TheE12seriescomesintwelvevaluesforeverydecade.E12系列每个十进制有十二个值；TheE24seriescomesintwentyfourvaluesperdecade.E24系列每个十进制也有二十四个值。E12series-10,12,15,18,22,27,33,39,47,56,68,82E24series-10,11,12,13,15,16,18,20,22,24,27,30,33,36,39,43,47,51,56,62,68,75,82,91E-24±1%，±2％，±5％E-96±1%Ｅ24系列适用于±1％、±2、±5％的产品，用3位数表示阻值，前2位有效数字，第3位代零的个数。阻值小于10Ω时，R是小数点。

E96系列适用于±1％的产品，用4位数表示阻值，前3位是有效数字，第4位代表零的个数。阻值小于100Ω时，R是小数点。

101112131516182022242730333639434751566268758291100102105107110113115118121124127130133137140143147150154158162165169174178182187191196200205210215221226232237243249255261267274280287294301309316324332340348357365374383392402412422432442453464475487499511523536549562576590604619634649665681698715732750768787806825845866887909931953976YouwillnoticewiththeE12valuesthateachsucceedingvaluefallswithintheplus/minus10%ofthepreviousvalues.

我们注意到对于E12每个连续的值之间相差上述值的±10%。Thisstemsfromtherealolddayswhenresistanceswerestatedaswithin20%tolerance(accuracy).过去对精度公差的描述是20%，Latervaluesofplus/minus5%tolerance后来的公差范围是±5%，ledtotheE24rangeofresistance.

形成了E24系列。

Quitecommontodayare2%tolerancemetalfilmstypes当今金属薄膜型的公差是2%，butforgeneralpurposeusewetendtosticktoE12valuesofresistanceineither1%,2%or5%tolerance.但是作为一般用途我们还是使用公差为1%，%2或%5的E12的电阻序列值。Costisthedeterminingfactor成本是决定因素，andmanyretailersnowstockthe2%rangeofresistanceasastandardtoaccommodatestockinglevelsandalsoatreasonablylowcost.如今许多零售商以2%公差的电阻作为库存调节量的标准，也能适当降低成本。Asexamplesofsaythe"22"types(red-red)fromtheE12seriesweget0.22,2.2,22,220,2,200,22,000,220,000and2,200,000oreightdecadesofresistors.正如例子中说到的出自E12系列中的“22”型，我们能够得到0.22、2.2、22、220、2200、22000、220000和2200000或者八位的十进制的电阻器。InmyopiniontheseoughttobereferredtorespectivelyasR22,2R2,22R,220R,2K2,22K,220Kand2M2.依我之见，上述各阻值应该各自表示为R22、2R2、220R、2K2、22K、220K和2M2。HeretheR,KandMholdplaceswherenodecimalpointsareusedtocauseconfusion.这里用R、K和M取代小数点的位置以免引起混淆。ConsiderifImeanttowrite(intheoldfashionedway)2.2Kinforacircuitvalue如果在电路中写入（以老的风格）2.2K值，butforgottotypeinthe"K"soyoujusthad2.2,wouldthecircuitwork?

忘记写字符“K”，仅仅写了2.2，那电路将如何工作？No!Howeasyisitforyoutoreaddecimalpointsabove.不行！而上面描述的那种读小数点方式，多么方便。Isn't2K2easiertoseeasmeaning2,200ohmsasagainst2.2K?

2K2不是比2.2K代表2200欧姆更容易吗？Whatifyoudidn'tseethedecimalpointin2.2K,couldn'titbetakentomean22Kor22,000ohms?如果没有看到2.2K的小数点，它不就被当作22K或22,000欧姆吗？NowyouknowwhyIprefertouse2K2or22Kor22R-noconfusion.现在你就知道为什么推荐用2K2或22K或22R——这不会引起混淆。Resistancecolorchartcodes3．电阻色表代码Hereinthislargecolorchartistheresistancecolorcode-learnthesequenceforever-这里大的色彩图表是电阻色彩代码——次序是一定要掌握的。BLACK,BROWN,RED,ORANGE,YELLOW,GREEN,BLUE,PURPLE,SILVER,WHITE黑，褐，红，橙，黄，绿，蓝，紫，银，白。Ihaveaccommodatedtwocurrentcolorbandingofresistances-fourbandandfivebandresistancecolorcode.我们已经推荐了两种通用的电阻色条——四条和五条色条电阻色码。ItshouldbeprettyselfexplanatoryIhope.它能够给出我想要的信息。Thefivebandcodeismorelikelytobeassociatedwiththemoreprecision1%and2%types.

五条码能够表示精确度1%和2%的类型的电阻。

Your"gardenvariety"5%generalpurposetypeswillbefourbandresistancecodes.作一般用途、精度为5%的电阻，“色彩变化”是通过四色条电阻代码来表示。

Capacitorn.电容器

capacitiveadj.电容性的

capacityn.电容量，能量，功率

capacitivereactance容抗

=capacityreactancereactancecapacity无功功率

capacitancen.容量，电容（值）

straycapacitance寄生电容

by-passcapacitor.旁路电容器

reservoircapacitor.

存储电容器;充电电容器

resonantcapacitor.谐振电容器WhatIsCapacitorinductorn.电感器

inductiveadj.电容性的

capacityn.电容量

inductivereactance感抗

inductancen.电感，感应

inductancecoil电感线圈

self[mutual]inductance

自【互】感（系数）amplifiern.放大器etc.inductanceamplifier电感耦合放大器

amplifierin[out]放大器输入【出】端

amplifierstage放大级

amplifiertube放大管etc.＝〔拉丁语〕常读作andsoforth等等.leadn.导线VHF30-300MHz甚高频UHF300-3000MHz特（超）高频powerline输电线dielectricsn.电介质

dielectricsconstant介电常数TheletterCstandsforcapacitance.Acapacitorisformedbytwoormoreconductiveparallelplatesseparatedbyaninsulatingmaterialordielectric.Typicaldielectricsyouwillencounterareair,mica,ceramicorplastic.

字母C代表电容。电容器是由两个或更多中间隔着绝缘物质或电介质的平行导电盘组成。典型的电介质是空气、云母、陶瓷或塑料。Consideranairvariablecapacitorofthetypeusedeitherasatrimmeroreventhetuningelementinaradio.Itismerelytwoormoreconductiveplatesseparatedbyair —isthisnotso?一个空气介质可调电容器常用作微调电容器或收音机中的调谐元件。它仅仅是两个或几个隔着空气的导电盘—不是吗？Gobacktoourinductorsabove,couldnotasimilardescriptionapplytothem?回到我们前面讲的电感器，类似的描述不能用于它们吗？Thatiswhyinductorsalsohavecapacitance!Wehavealsolearntasmallpieceofwirehasinductance.Thisiswhycapacitorswithleadsetc.exhibitinductance.

那就是为什么电感器具有电容！我们也知道一小截导线具有电感。这就是带有引线等的电容器存在电感的原因。Atsomepointourinductorwithitsinherentcapacitance(calledstray)willresonate(youwilllearnaboutthatlater)andthisiscalleditsselfresonantfrequency.Thesameruleappliestocapacitors.MostlyitisonlytheVHFandUHFaficionadowhohastobegreatlyconcernedabouttheseproperties.Straycapacitanceiseverywhere.Sometimesitcanbeusedtoadvantage,usuallyyoutakeitintoaccount(thatisanotherfunctionoftrimmers)butoftenit’samonumentalpain.

具有寄生电容的电感器在某些点会发生谐振，成为固有谐振频率。同样的规则可以运用于电容器。通常只有VHF/UHF的发烧友会不得不担心这些特性。寄生电容随处可见。有时它也有好处，通常我们会考虑到它，但它经常是非常痛苦的。Isaidmostly—whichmeansifyouforgetaboutit,thenyoucansurelyguaranteeonedaythispropertywillbiteyou.Thatwillbethedaywhenyou’reworkingonyourpetproject,whichofcoursewon’tworkasexpectedandyoudon’tknowwhyyourtheorydoesn’tworkoutintherealworld—another“gotcha”.

我说通常，意味着如果你忘了，保证会有一天，这个特性会咬住你。那将是这么一天:你的宝贝工程不能象你预期的那样工作，而你不知道为什么理论在现实世界中不能工作。另一个我抓住你的把柄了。['gɒtʧə]Straycapacitanceinsloppylayoutscanaccountforunexpectedoscillations,nooscillations,differentcircuitresponsesandgenerallycauseyouto“becomeavictimofthebottle,eternallycaughtinthegripofthegrapeand,ifyoubecomelikeme,occasionallyruinanotherwisegoodkeyboardwithanevenmuchbetterclaret.”草率布线中的寄生电容是产生意料之外震荡、没有震荡、不同电路响应的原因，常常把你变成瓶子的牺牲品，永远的被葡萄酒掌握，如果你变得像我一样，偶尔用更好的葡萄酒毁坏一个相当好的键盘。Eventhebestofdesignsandcarefullayoutsareaffected.Notonlystraycapacitancebutstrayinductancecanaffectyou.Trysomehighspeed,doublesided,digitalPCBdesigns.甚至最好的设计和仔细的布线都会受影响。不仅寄生电容，寄生电感也会影响你。试一试用高速，双面的数字印刷线路板设计。Backtocapacitors.Apartfromtheirusesinresonantcircuitstheyareusedas:回到电容器。除了在谐振电路中的应用外，它们被用于：(1)DCblockingdevices—AcapacitorwillpassACorRFbutnotDC.Thatisoftenthefunctionofcouplingcapacitorsincircuits.ThecouplingcapacitorwillpassourrequiredsignalbutblocktheDCsupplyfromthepreviousstagee.g.0.001mF(1 000pFor1nF).隔直元件电容器能够通过交流或射频信号，直流则不行。那是电路中耦合电容的作用。耦合电容让需要的信号通过，隔离前级的直流电源。例如：0.001μF(1 000pFor1nF).(2)supplyby-passcapacitor —AcapacitorusedtopassACorRF.Examplesincludeby-passofaDCsupplytoanemitterby-passcapacitor.WhenusedonaDCsupplylinethecapacitorshunts(shorts)togroundanyunwantedACorRFtoavoidcontaminationofoursupplye.g.0.1μF(100000pFor100nF).电源旁路电容电容器被用于通交流或射频。包括直流电源和射极旁路电容。当用于直流电源綫时，电容对地短路，能避免任何不想要的交流或射频污染电源。例如0.1mF(100000pFor100nF).(3)reservoirby-passcapacitor —UsedintheoutputofaDCrectifiertosmoothoutthepowerlineACpulsesandasareservoirbetweenthechargingpulses.Thinkofitasabigwaterstoragetank.Thisiswhereyouhavethehighvaluecapacitorse.g.10 000mF/63V (10000U).存储电容用于直流整流器的输出端用以消除电源线上的交流脉冲和作为两个充电脉冲间的存储器。可以把它想象成一个大的储水容器。这时要用大电容例如10 000μF/63V (10000U).(4)emitterby-passcapacitor —Inthecaseofanemitterby-passourtransistormay,asoneexample,beconsideredastwodistinctmodels,oneunderDCconditionswhichsetsuphowwewantthetransistortooperateandanotherunderACorRFconditionse.g.asanamplifier.Inthiscaseouremitterby-passcapacitormerelymakesanyemitterresistorinvisibleforACorRFpurposestypicalvaluesmightrangefrom2.2μFdownto0.1μF.(2U2downto100N)就射极旁路而言，晶体管可以当作两个不同的模型，一个在直流状态将晶体管置于我们需要的运行状态，另一个在交流状态，例如放大器。既然是这样射极旁路电容只是使射极电阻在交、射场合不可见。典型值范围在2.2μF到0.1μF.ParrallelplatecapaciorshaveaformulaforcalculatingcapacitanceC=0.22248K(A/t)WhereC=capacitanceinpFK=dielectricconstant(air=1)A=areaofplateordielectrict=thickofdielectricorspacinginthecaseofairvariables(5)Seriesorparrallelcapacitors-seriesandparallelcombinationscalculateinoppositefashiontoinductors,i.e.parallelareCtotal=C1+C2+…+CnAndseriesareCtotal=1/[1/C1+1/C2+1/Cn]Nowherecomesomeveryusefulformula.Usingtheoneimmediatelyaboveyoushoulddeterminethata22pfcapacitorinserieswitha15pfcapacitorgivesatotalof8092pf.Goaheaddoit!Checkmeout.Whatifwehavesay105pfalreadyincircuitandneededtoreduceittosay56pf.Arealworldexamplemightbesaytheonlyairvariablecapacitoravailableisonewithamaximumof105pf.whatdoyouputinseriestoreducethemaximumto56pf?Didyouknowtheformulaabove?Ifyoudisbelievemethencheckitoutusing**aboveasadoublecheck.Writeitinyourexercisebook.Ifthat’sflashtrythisred-hotformula.Supposewewantanoscillatortotunefrom7MHZto7.2MHZ.Nowifyoudon’tquiteknowwhatanoscillateisyetdon’tworry.Forreasonswewillexplorelateroninthetutorialsyouwillfindthatyourcapacitancemustvary,fortuningpurpose,inthedirectratioofthefrequencyratiosquaredorCmaxtoCmin=(Fhigh/Flow)2.InthisexampleourfrequencyratioisFhigh/Flow=7.2/7.0=1.0287.ourretiomustbesquaredsotheitbecomes1.02872=1.05796.thismustbeourcapacitanceretioi.e.CmaxtoCmin=1.05796nucleusn.核子['nju:kli:əs]

atomn.原子['ætəm]protonn.质子['prəu,tɒn]

electronn.电子freeelectron自由电子electrochemicaladj.电气化学的ElectricBasicConceptneutralstate中性状态,electroneutrality

n.电中性beelectricallyneutral电性呈中性orbitn.轨道；轨迹

orbitalelectron轨道电子[nju:'træləti]gravityn.地心引力,重力accelerationofgravity重力加速度thecentreofgravity重心，重点specificgravity比重null[zero]gravity无重力，失重chargen.负荷,电荷,费用,充电negativecharge负电荷positivecharge正电荷chargedensity电荷密度like-charged电性相同的attractv.吸引attractionn.吸引,吸引力,oppositesattract异性吸引

repelv.排斥repulsionn.排斥magneticadj.磁的,有磁性的,有吸引力的magneticfield

磁场electricfield

电场linesofforce力线currentflow电流electromotiveforce=EMF电动势counter-electromotiveforce=CEMF反电动势potentialadj.势的,位的(electric)potentialdifference电位差adifferencebypotentialignorevt.忽略，不理睬,忽视alternatorn.交流发电机['):ltə,neitə]alternateadj.交替的alternatingcurrent交流电流alternating-current交流（电）的generatorn.发电机motorn.电动机voltagesources电压源amagneticinduction电磁感应terminaln.终端,接线端,电路接头kilovoltn.千伏特millivoltn.毫伏(特)(=1/1000伏(特),略作mV或mv)microvoltn.微伏(等于1伏特的百万分之一)

1.Electriccharge电荷1.1neutralstateofanatom

1.1中性的原子Elementsareoftenidentifiedbythenumberofelectronsinorbitaroundthenucleusoftheatomsmakinguptheelementandbythenumberofprotonsintheatom.元素是通过组成该原子的核子轨道上的电子数及核子中的质子数来区分的。Ahydrogenatom,forexample,hasonlyoneelectronandoneproton.例如，一个氢原子只有一个电子和一个质子。Analuminumatom（illustrated）has13electronsand13protons.一个铝原子有13个电子和13个质子（如图）。Anatomwithanequalnumberofelectronsandprotonsissaidtobeelectricallyneutral.一个有相同数目的电子和质子数的原子电性呈中性。1.2positiveandnegativecharges

正负电荷Electronsintheouterbandofanatomareeasilydisplacedbytheapplicationofsomeexternalforce.原子的外圈的电子很容易由于受到外力的作用而被移走。Electronswhichareforcedoutoftheirorbitscanresultinalackofelectronswheretheyleaveandanexcessofelectronswheretheycometorest.由于电子从轨道移走而造成该原子缺少电子，而移入电子的原子电子过剩。Thelackofelectronsiscalledapositivechargebecausetheraremoreprotonsthanelectrons.使由于质子数多于电子数，缺少电子的成为正电荷。Theexcessofelectronshasanegativecharge.电子过剩的称为负电荷。Apositiveornegativechargeiscausedbyanabsenceorexcessofelectrons.电子不足或过剩产生正或负电荷。Thenumberofprotonsremainsconstant.质子数始终是恒定不变的。

1.3attractionandrepulsionofelectriccharge电荷之间的吸引和排斥Theoldsaying,”oppositesattract”istruewhendealingwithelectriccharges.俗话说，“异性吸引”，处理电荷时是正确的。Chargedbodieshaveaninvisibleelectricfieldaroundthem.每个电荷四周有一个看不见的电场。Whentwolike-chargedbodiesarebroughttogether,theirelectricfieldwillworktorepelthem.当两个电性相同的电荷靠近时电场将相斥，Whentwounlike-chargedbodiesarebroughttogether,theirelectricfieldwillworktoattractthem.当两个电性不同的电荷靠近时电场将相吸。Theelectricfieldaroundachargedbodyisrepresentedbyinvisiblelinesofforce.电荷周围的电场通过不可见的电力线表示，Theinvisiblelinesofforcerepresentaninvisibleelectricfieldthatcausestheattractionandrepulsion.不可见的电力线表示引起吸引和排斥的不可见的电场。Linesofforceareshownleavingabodywithapositivechargeandenteringabodywithanegativecharge.正电荷用离开的电力线表示、负电荷用进入的电力线表示。

2.Current电流

Electricityistheflowoffreeelectronsinaconductorfromoneatomtothenextatominthesamegeneraldirection.电是在导体中的从一个原子以相同方向流向下一个原子的自由电子流。Thisflowofelectronsisreferredtoascurrentandisdesignatedbythesymbol”I”.这种电子流就是电流，由符号表示为“I”。Electronsmovethroughaconductoratdifferentratesandelectriccurrenthasdifferentvalues.电子以不同的速度流过导体，电流有不同的值。Currentisdeterminedbythenumberofelectronsthatpassthroughacross-sectionofaconductorinonesecond.电流的大小由在一秒中内流过导体横截面的电子数量所决定。Wemustrememberthatatomsareverysmall.我们必须记住原子是非常小的。Ittakesabout1,000,000,000,000,000,000,000,000atomstofullonecubiccentimeterofacopperconductor.在一立方厘米的铜导体中有1,000,000,000,000,000,000,000,000个原子。

Thisnumbercanbesimplifiedusingmathematicalexponents.这个数字可以用数学的指数形式来化简，Insteadofwriting24zerosafterthenumber1,write1024.用1024来代替24个零。Tryingtomeasureevensmallvaluesofcurrentwouldresultinunimaginablylargenumbers.试图测量如此微小的电流将产生难以想象的巨大的数字。Forthisreasoncurrentismeasuredinampereswhichisabbreviated”amp”.所以，电流用安培数来度量，安培可以简写为“amps”。Thesymbolforampistheletter:A”.安培可以用符号“A”来表示。Acurrentofoneampmeansthatinonesecondabout6.24×1018electronsmovethroughacross-sectionofconductor.一安培的电流意味着在一秒中之内有6.24×1018个电子流过导体的截面。Thesenumbersaregivenforinformationonlyandyoudonotneedtobeconcernedwiththem.这些数字只是信息，并不需要去关心。Itisimportant,thattheconceptofcurrentflowbeunderstood.但是重要的是理解电流的概念。

2.1unitsofmeasurementforcurrent测量电流的单位Thefollowingchartreflectsspecialprefixesthatareusedwhendealingwithverysmallorlargevalueofcurrent:下面的图表反映了处理很小和很大的电流时的计量单位的词头：Prefix词头symbol符号decimal十进制1kiloampere1千安1KA1000A1milliampere1毫安1mA1/1000A1microamoere1微安1μA1/1000000A2.2

directionofcurrentflow电流的方向Someauthoritiesdistinguishbetweenelectronflowandcurrentflow.一些权威将电子流和电流区分，Conventionalcurrentflowtheoryignorestheflowofelectronsandstatesthatcurrentflowsfrompositivetonegative.传统上电流理论忽略电子流，而认为电流是从正极流向负极。Toavoidconfusion,wewillusetheelectronflowconceptwhichstatesthatelectronsflowfromnegativetopositive.为了避免混淆，我们使用电子流概念是电子从负极流向正极。

3.voltage电压Electricitycanbecomparedwithwaterflowingthroughapipe.电可与流过管子的水相比较。Aforceisrequiredtogetwatertoflowthroughapipe.水流过管子需要一个力的作用，Thisforcecomesfromeitherawaterpumporgravity.这个力来自水泵或水的重力。Voltageistheforcethatisappliedtoaconductorthatcauseselectriccurrenttoflow.电压就是作用于导体上的引起电流流动的力。Electronsarenegativeandareattractedbypositivecharges.电子的电性是负的并能被正电荷吸引，Theywillalwaysbeattractedfromasourcehavingaexcessofelectrons,thushavinganegativecharge,toasourcehavingadeficiencyofelectronswhichhasapositivecharge.电子总是从由于多余电子而呈负电荷的地方到由于缺乏电子而呈现电荷为正的地方。Theforcerequiredtomakeelectricityflowthroughaconductoriscalledadifferencebypotential,electromotiveforce(emf),ormoresimplereferredtoasvoltage.这种使得电子流过导体的力叫做电势差、电动势或简单地称为电压。Voltageisdesignatedbytheletter”U”,ortheletter“V”.电压用字符“E”或“V”表示。Theunitofmeasurementforvoltageisvoltwhichisdesignatedbytheletter“V”.度量电压的单位是伏特，伏特用字符“V”表示。

3.1voltagesources电压源Anelectricvoltagecanbegeneratedinvariousways.可以有多种产生电压的方式。Abatteryusesanelectrochemicalprocess.电池利用电化学过程，Acar’salternatorandapowerplantgeneratorutilizeamagneticinductionprocess.而汽车的发电机和电厂的发电机是利用电磁感应作用。Allvoltagesourcessharethecharacteristicofanexcessofelectronsatoneterminalandashortageattheotherterminal.所有的电压源共有的特性是在一端电子多余并在另一端电子不足，Thisresultsinadifferenceofpotentialbetweenthetwoterminals.这就导致了在两端具有不同的电势。3.2voltagesymbol电压符号Theterminalsofabatterya