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1、Chapter1ElectricandElectronicTechnologyFundamentalsUnit1ElectricElementsandComponentsTextNewWordsandExpressionsExercisesEndUnit1ElectricElementsandComponentsIntroductionElectricalelementsareconceptualabstractionsusedintheanalysisofelectricalnetworks.Anyel
2、ectricalnetworkcanbeanalyzedasmultiple,interconnectedelectricalelementsinaschematicdiagramorcircuitdiagram,eachofwhichaffectsthevoltageinthenetworkorcurrentthroughthenetwork.Theseidealelectricalelementsrepresentreal,physicalelectricalorelectroniccomponent
3、sbuttheydonotexistphysicallyandtheyareassumedtohaveidealpropertiesaccordingtoalumpedelementmodel,whilecomponentsareobjectswithlessthanidealproperties,adegreeofuncertaintyintheirvaluesandsomedegreeofnonlinearity,eachofwhichmayrequireacombinationofmultiplee
4、lectricalelementsinordertoapproximateitsfunctions.Circuitanalysisusingelectricelementsisusefulforunderstandingmanypracticalelectricalnetworksusingcomponents.Byanalyzingthewayanetworkisaffectedbyitsindividualelementsitispossibletoestimatehowarealnetworkwil
5、lbehave.Unit1ElectricElementsandComponentsTheelementsThefourfundamentalcircuitvariablesarecurrent,I;voltage,V,charge,Q;andmagneticflux,Φ.Only5elements,producedbymanipulatingthesefourvariables,arerequiredtorepresentanycomponentornetworkinaLinearsystem.Twos
6、ources:·Currentsource,measuredinamperes-producesacurrentinawire.Anidealcurrentsourceisamathematicalmodel,whichrealdevicescanonlyapproachinperformance.Thecurrentthroughanidealcurrentsourceisindependentofthevoltageacrossit.Unit1ElectricElementsandComponents
7、·Voltagesource,measuredinvolts-producesapotentialdifferenceacrosstwopoints.Anidealvoltagesourceisonlyexistsinmathematicalmodelsofcircuits.Similarly,thevoltageacrossanidealvoltagesourceisindependentofthecurrentthroughit.Threepassiveelements:·ResistanceR,me
8、asuredinohms-producesavoltageproportionaltothecurrentflowingthroughtheelement.Relatesvoltageandcurrentaccordingtotherelation·CapacitanceC,measuredinfarads-producesacurrentproportionaltotherateofchangeofvoltageacross