E磁场对电流的作用.ppt

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1、Chapter8MagneticForceonCurrents§1MagneticforceoncurrentsAmpere’slaw§2Magneticfieldactsonaloopofwire§3Theworkofmagneticforce§4Lorentzforce§5Chargedparticlemovinginelectricandmagneticfield§6Halleffect§1MagneticforceoncurrentAmpere’slaw1Experiment实验现象Acurrent-carryingwireinamagneticfi

2、eldexperienceaforce：IfwireisperpendiculartoB，theforce：F=IBL；IfwireisparalleltoB，theforce：F=0；IftheanglebetweenwireandBisα,theforce:F=IBLsinαForcedirectionisdeterminedbylefthandrule.2Ampere’slawMagnitude：Direction：Forceontotalcurrent:3ExamplesEx1determinetheforcebetweentwoparallelst

3、raightwiresI1，I2，0，aa0I1I2Thefieldbywire(I1)atwire(I2):MagneticforceoncurrentelementDirectionasshowninFigTheforceperunitlengthwire取a=1m,f=210-7N/m,I=1AParallelwirescarryingcurrentinthesamedirectionattractoneanotherEx2determinetheforceonasemicircularsectionofwireofradiusRcarryin

4、gacurrentIinamagneticfield.Discuss(1)TheforceonrigidcircularwireCorollary:任一段弯曲载流导线在均匀磁场中所受的磁场作用力，等于从起点到终点连接的直导线通过相同的电流时所受的作用力。(2)刚性1/4圆线圈受力(3)连接两端点的直线电流受力方向:与x轴夹角/4yxOIEx3Twocurrent-carryingwiresisshowninFig(MNiscoplanarwithwireI1).CalculatetheforceonwireMN.Magneticforceoncurrent

5、elementI2dl：MagneticforceonMN:ThefieldbycurrentI1atcurrentI2:DirectiondownintopageDirection:asshownintheFigMFxI2dl300aNI1b§2Magneticfieldactsonaloopofwireabcdad=bc=l1ab=cd=l2Result：Acurrent-carryingloopinamagneticfieldexperiencesatorquebc：downwardsda：upwardsab：a(b)d(c)⊙Directionas

6、showninFigcd：equalandopposite,buttheydonotactalongthesameline,sotheycreateatorque(力矩)TorqueM＝IBl1l2cos=IBScosIINotea(b)d(c)⊙(1)Themagnetictorque(2)Extremumofmagnetictorque=π/2：M=Mmax=0：M=0Stableequilibrium=π:M=0Unstableequilibrium(3)CarryingcurrentloopinuniformmagneticfieldTh

7、eforceontheloopofuniformmagneticfieldiszero.Thetorqueontheloopofuniformmagneticfieldisnotzero.Appendix:(1)AcurrentloopofanyshapeAlthoughtheequationisarrivedforthespecialcaseofarectangularloop,therelationcanbegeneralizedtoacurrentloopofanyshapebyapproximatingtheloopascloselyasdesire

8、dbyanumberofrectangularloo