磁性材料的特性.pptx

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1、CHAPTER16MAGNETICPROPERTIESOFMATERIALS16.1EffectonMagneticFieldbyMaterials16.2Magnetization16.3VectorHandItsCircuitalTheorem16.4MagneticShielding16.1EffectonMagneticFieldbyMaterialsTheinteractionbetweenmagneticfieldsandmaterialscanbeTheinteractionbetweenmagneticfieldsandmaterialscanbeobservedexperim

2、entally.Themostsimplemethodistousealongobservedexperimentally.Themostsimplemethodistousealongstraightwithvacuumorairinsidefirst(Fig.16.1(a)andmeasurethestraightwithvacuumorairinsidefirst(Fig.16.1(a)andmeasurethemagneticfieldinitwhencurrentIisflowinginthecoils.magneticfieldinitwhencurrentIisflowingin

3、thecoils.Nextfillthesolenoidwithsomematerialandthenmeasureagainthemagneticfieldinitwhenthesamecurrentisledinthecoils(Fig.16.1(a).LetB0andBbethemagneticfieldmeasuredinthetwocasesrespectively.Experimentalresultsshowthatthetwodifferfromeachotherandcanrelatedas16.2MagnetizationInanatom,theelectronsorbit

4、aroundthenucleusandhavealsospin.Inanatom,theelectronsorbitaroundthenucleusandhavealsospin.Thenucleusalsohasspin.ThesemotionallfromequivalentcircularThenucleusalsohasspin.Thesemotionallfromequivalentcircularelectriccurrents.Asawholethesemotionsofchargesinamoleculeelectriccurrents.Asawholethesemotions

5、ofchargesinamoleculemaybeconsideredasconstituteasinglemicroscopiccircularcurrentmaybeconsideredasconstituteasinglemicroscopiccircularcurrentcalledcalledmolecularcurrentmolecularcurrentiwithiwithmolecularmagneticmomentmolecularmagneticmomentm.m.Example16.1Alongstraightsolenoidofnturnperunitlengthisfi

6、lledExample16.1Alongstraightsolenoidofnturnperunitlengthisfilledinsidewithuniformmaterialofrelativepermeability.Findthesurfaceinsidewithuniformmaterialofrelativepermeability.Findthesurfaceboundcurrentdensityonthesurfaceofthematerialinthesolenoid.boundcurrentdensityonthesurfaceofthematerialinthesolen

7、oid.16.3VectorHandItsCircuitalTheorem16.4MagneticShieldingWhenabockofferromagneticWhenabockofferromagneticmaterialisputinamagneticmaterialisputinamagneticfield.Sinceitsisverylarge.field.Sinceitsisverylarge.ThesurfaceboundcurrentThesurfaceboundcurrentproducedbymagnetizationisproducedbymagnetizationis

8、verylarge.Thesuperpositionofverylarge.Thesuperpositionofthemagneticfieldproducedbythemagneticfieldproducedbytheseboundcurrentsonthetheseboundcurrentsontheoriginalexternalfieldwouldoriginalexternalfieldwouldchargethedistributionofthechargethedistributionofthelaterdrastically.Pictorially,thelaterdrast

9、ically.Pictorially,theresultantfieldlineswouldberesultantfieldlineswouldbeconcentratedorcollectedintheconcentratedorcollectedintheferromagneticmaterialasferromagneticmaterialasshowninFig.16.4.showninFig.16.4.Iftheferromagneticmaterialsismadetohaveahollowinterior,suchasanironbox,themagneticfieldlineswouldbecollectedintheironwallasshowninFig.16.5Inthehollowspaceinthebox,themagneticfieldwouldbeveryweak.Thuswhensomethingisputintheclosedbox.Itwillnot(oronlyslightly)beaffectedbyexternalmagneticfields.Thisistheprincipleofmagneticshieldingusingironbox.SUMMARY