《大学物理简明教程》 课件 16-2 Reactances

AlternatingVoltagesandCurrentsPowerinACCircuitsandRMSValuesRectification-DiodeCapacitorsandInductorsinACCircuits-Reactance&phasedifferenceRLCCircuits–ReactanceandImpedanceResonanceinElectricalCircuitsContentsofACCircuitsCapacitorwithACvoltage

orinadvanceACvoltageiscalledthereactance-“capacitivereactance”

=R?Inversely

proportionaltothefrequency!unit-ΩCalculatethecapacitivereactanceofa5.00μFcapacitorwhen60Hzand10kHzvoltagesareappliedWhatisthermscurrentateachfrequencyiftheappliedrmsvoltageis120V?ComparewithresistorswithACvoltage?nophasedifferenceVR

=IRRC

Solution?PhasedifferencebetweenVandIBothresistorandcapacitor?PhasedifferencebetweenVandI

circuitis“purely

capacitive”

circuitis“resistive”asifthecapacitorisjustawire,allowingcurrenttopassMaybehighfrequencyCapacitorsblockthelowfrequencies(includingDC)letthehighfrequenciespassthroughInductorinACcircuit

Or

isthephasedifferenceI

lagsbehind

Reactance

isthe“inductivereactance”

proportionaltothefrequency!Calculatetheinductivereactanceofa3.00mHinductorwhen60Hzand10kHzvoltagesareappliedWhatisthermscurrentateachfrequencyiftheappliedrmsvoltageis120V?letthelowfrequencies(includingDC)passthroughInductorsblockthehighfrequenciesVR

=IRR

Inductorwithresistor

PowerinCapacitorsC=2.0FWewanttoknowInstantaneousPowerAveragePowerPowerflowsintoandoutofcapacitorNo

net

powerisconsumedbycapacitor

PowerininductorsPowerflowsintoandoutofinductorNonet

powerisconsumedbyinductor

SimilartocapacitorOnlyresistorscontributetotheaveragepower(consumed),intheformofJouleheatingReactancecapacitiveinductiveresistiveExpressionRPhasedifferenceI

leadsV

by

π/2I

lagsbehindby

π/2I

and

V

inphaseHighfrequencyequivalentc