电子信息与通信工程专业英语lesson2-1[001].ppt

2020 3 19 可编辑 1 Chapter2CircuitSystemandDesign Outline2 1CircuitandSystem2 2AnalogandDigitalCircuitsDesign2 3RadioReceiverCircuit 2020 3 19 可编辑 2 2 1CircuitandSystem OutlineBasicconceptsCircuitandSystem 2020 3 19 可编辑 3 Terminology chargen 负荷 电荷 费用 主管 充电 充气 装料conductivityn 传导性 传导率insulatorn 绝缘体 绝热器gravitationaladj 重力的voltagen 电工 电压 伏特数voltsn 直流电压amperen 安培ohmn 物 欧姆coulombn 电 库仑 电量单位 diametern 直径inductancen 感应系数 自感应 2020 3 19 可编辑 4 dielectricn 电介质 绝缘体adj 非传导性的faradn 电 法拉 电容单位 polarityn 极性potentialdifference 电 电位差 电势差equivalentresistance等效电阻SuperpositionTheorem叠加定理Thevenin sTheorem戴维南定理Norton sTheorem诺顿定理 2020 3 19 可编辑 5 IntheBohrtheoryoftheatom namedafterNielsBohr 1885 1962 electronsorbitanucleuscontainingneutronsandprotons Electricchargeismeasuredincoulombs Thisrelativemobilityofelectronswithinamaterialisknownaselectricconductivity Conductivityisdeterminedbythetypesofatomsinamaterial thenumberofprotonsineachatom snucleus determiningitschemicalidentity andhowtheatomsarelinkedtogetherwithoneanother Introduction Texttour BasicconceptsChargeandconductivity 2020 3 19 可编辑 6 Itshouldalsobeunderstoodthatsomematerialsexperiencechangesintheirelectricalpropertiesunderdifferentconditions Whilethenormalmotionof free electronsinaconductorisrandom withnoparticulardirectionorspeed electronscanbeinfluencedtomoveinacoordinatedfashionthroughaconductivematerial Thisuniformmotionofelectronsiswhatwecallelectricity orelectriccurrent Therecanbeelectriccurrentonlywherethereexistsacontinuouspathofconductivematerialprovidingaconduitforelectronstotravelthrough Ifthepathisblocked the flow willnotoccur 2020 3 19 可编辑 7 Electriccircuits voltageandcurrent Anelectriccircuitisformedwhenaconductivepathiscreatedtoallowfreeelectronstocontinuouslymove Thiscontinuousmovementoffreeelectronsthroughtheconductorsofacircuitiscalledacurrent anditisoftenreferredtointermsof flow justliketheflowofaliquidthroughahollowpipe Theforcemotivatingelectronsto flow inacircuitiscalledvoltage whichtechnicallyisameasureofpotentialenergyperunitchargeofelectrons Themoremasssomethinghasandthehigherweliftit themorepotentialenergyithas 2020 3 19 可编辑 8 Onevoltisdefinedasthatmagnitudeofelectromotiveforcerequiredcauseacurrentofoneamperetopassthroughaconductorhavingaresistanceofoneohm CurrentflowisrepresentedbythelettersymbolI Thebasicunitinwhichcurrentismeasuredistheampere amp Oneampereofcurrentisdefinedasthemovementofonecoulombpastanypointofaconductorduringonesecondoftime 2020 3 19 可编辑 9 Freeelectronstendtomovethroughconductorswithsomedegreeoffriction oroppositiontomotion Thisoppositiontomotionismoreproperlycalledresistance TheresistanceofamaterialthatfollowsOhm slawisconstant orindependentofvoltageorcurrent andtherelationshipbetweencurrentandvoltageislinear Wheneveranelectricvoltageexistsbetweentwoseparatedconductors anelectricfieldispresentwithinthespacebetweenthoseconductors Electricalenergycanbestoredinanelectricfield Thedevicetobecapableofdoingthisiscalledacapacitororacondenser Resistance capacitanceandinductance 2020 3 19 可编辑 10 Ifacondenserisconnectedtoabattery theelectronswillflowoutofthenegativeterminalofthebatteryandaccumulateonthecondenserplateconnectedtothatside Thusthecondenserissaidtobecharged Thecapacitanceisdirectlyproportionaltothedielectricconstantofthematerialandtotheareaoftheplatesandinverselytothedistanceoftheplates Thelargertheplatearea thesmallerthespacebetweenthem thegreaterthecapacitance Wheneverelectronsflowthroughaconductor amagneticfieldwilldeveloparoundthatconductor Thiseffectiscalledelectromagnetism Magneticenergycanbestoredinamagneticfield Thedevicetobecapableofdoingthisiscalledaninductor 2020 3 19 可编辑 11 Tostoremoreenergyinaninductor thecurrentthroughitmustbeincreased Thismeansthatitsmagneticfieldmustincreaseinstrength andthatchangeinfieldstrengthproducesthecorrespondingvoltageaccordingtotheprincipleofelectromagneticself induction Whenthecurrentthroughaninductorisincreased itdropsavoltageopposingthedirectionofelectronflow actingasapowerload Inthisconditiontheinductorissaidtobecharging becausethereisanincreasingamountofenergybeingstoredinitsmagneticfield Notethepolarityofthevoltagewithregardtothedirectionofcurrent 2020 3 19 可编辑 12 2 CircuitandSystem Ohm sLawThefirst andperhapsmostimportant relationshipbetweencurrent voltage andresistanceiscalledOhm sLaw discoveredbyGeorgSimonOhmin1827 Ohm sprincipaldiscoverywasthattheamountacircuitisdirectlyproportionaltothevoltageofelectriccurrentthroughametalconductorinimpressedacrossit foranygiventemperature Ifweknowthevaluesofanytwoofthethreequantities voltage current andresistance inacircuit wecanuseOhm sLawtodeterminethethird 2020 3 19 可编辑 13 Kirchoff sCurrentLawandKirchoff sVoltageLawKirchoff sCurrentLawisthetotalchargeflowingintoanodemustbethesameasthetotalchargeflowingoutofthenode Kirchhoff sVoltageLaw orKirchhoff sLoopRule isaresultoftheelectrostaticfieldbeingconservative Itstatesthatthetotalvoltagearoundaclosedloopmustbezero Ifthiswerenotthecase thenwhenwetravelaroundaclosedloop thevoltageswouldbeindefinite 2020 3 19 可编辑 14 IntroductiontonetworktheoremsInelectricnetworkanalysis thefundamentalrulesareOhm sLawandKirchhoff sLaws Whilethesehumblelawsmaybeappliedtoanalyzejustaboutanycircuitconfiguration evenifwehavetoresorttocomplexalgebratohandlemultipleunknowns therearesome shortcut methodsofanalysistomakethematheasier 2020 3 19 可编辑 15 SuperpositionTheoremThestrategyusedintheSuperpositionTheoremistoeliminateallbutonesourceofpowerwithinanetworkatatime usingseries parallelanalysistodeterminevoltagedrops and orcurrents withinthemodifiednetworkforeachpowersourceseparately Then oncevoltagedropsand orcurrentshavebeendeterminedforeachpowersourceworkingseparately thevaluesareall superimposed ontopofeachother addedalgebraically tofindtheactualvoltagedrops currentswithallsourcesactive 2020 3 19 可编辑 16 Thevenin sTheoremThevenin sTheoremstatesthatitispossibletosimplifyanylinearcircuit nomatterhowcomplex toanequivalentcircuitwithjustasinglevoltagesourceandseriesresistanceconnectedtoaload Thevenin sTheoremisespeciallyusef