电气工程及自动化专业英语55.1 IntroductionMagnetismhasbeenstudiedformanyyears.Somemetalsintheirnaturalstateattractsmallpiecesofiron.Thispropertyiscalledmagnetism.Materialsthathavethisabilityarecallednaturalmagnets.Thefirstmagnetsusedwerecalledlodestones.Now,artificialmagnetsaremadeinma...
5.1 IntroductionMagnetismhasbeenstudiedformanyyears.Somemetalsintheirnaturalstateattractsmallpiecesofiron.Thispropertyiscalledmagnetism.Materialsthathavethisabilityarecallednaturalmagnets.Thefirstmagnetsusedwerecalledlodestones.Now,artificialmagnetsaremadeinmanydifferentstrengths,sizes,andshapes.Magnetismisimportantbecauseitisusedinelectricmotors,generators,transformers,relays,andmanyotherelectricaldevices.Theearthitselfhasamagneticfieldlikealargemagnet.5.2 PermanentMagnetsFig.5-1 Magneticfluxlinesdistortedthroughapieceofiron5.2 PermanentMagnetsFig.5-2 Horseshoemagnet5.3 MagneticFieldAroundConductorsandaCoil5.3.1 MagneticFieldAroundConductors5.3.2 MagneticFieldAroundaCoil5.3.3 Electromagnets5.3.1 MagneticFieldAroundConductorsFig.5-3 Thedirectionrelationshipofcurrentflowandmagneticflux5.3.2 MagneticFieldAroundaCoilFig.5-4 Magneticfiledaroundaloopofwire5.3.2 MagneticFieldAroundaCoilFig.5-5 Magneticfiledaroundacoilofwire5.3.3 ElectromagnetsFig.5-6 Magneticfiledaroundacoilofwirewithacore5.4 Ohm’sLawforMagneticCircuitsArelationshipsimilartoOhm’slawforelectricalcircuitsexistsinmagneticcircuits.Magneticcircuitshavemagnetomotiveforce(MMF),magneticflux(Φ),andreluctance(R).MMFistheforcethatcausesamagneticfluxtobedeveloped.Magneticfluxconsistsofthelinesofforcearoundamagneticmaterial.Reluctanceistheoppositiontothedevelopmentofamagneticflux.Thesetermsmaybecomparedtovoltage,current,andresistanceinelectricalcircuits.5.5 DomainTheoryofMagnetismAtheoryofmagnetismwaspresentedinthenineteenthcenturybytheGermanscientistWilhelmWeber.Weber’stheoryofmagnetismwascalledthemoleculartheory.Itdealtwiththealignmentofmoleculesinmagneticmaterials.Weberfeltthatmoleculeswerealignedinanorderlyarrangementinmagneticmaterials.Innonmagneticmaterials,hethoughtthatmoleculeswerearrangedinarandompattern.5.6 ElectricityProducedbyMagnetism1.magnetism2.electromagnetism3.magnet4.magnetic5.clockwise6.counterclockwise7.compass8.loop9.coil10.turns11.winding12.flux5.6 ElectricityProducedbyMagnetism13.magnetomotive14.molecular15.align16.generator17.magnetic18.induction19.slip20.carbon21.commutator22.reluctance5.6 ElectricityProducedbyMagnetismFig.5-7 BasicACgenerator
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