5 steady electric currentnew

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1、Chapter5SteadyelectriccurrentsConductioncurrents:Driftmotionofconductionelectronsofholesinconductororsemicond.Electrolyticcurrents:Migrationofpositiveor/negativeions.Convectioncurrents:Motionofelectionsionsinvacuum.Kirchhoff’svoltagelaw:ElectromotiveforceKirch

2、hoff’scurrentlaw:ConservationofchargeOhm’slaw:V=IR5-2CurrentDensity&Ohm’slawΔQKKΔQ=Nqu⋅aˆΔSΔt(Volume)currentdensity，JnKK2ThechargepassingthroughthesurfaceΔSJ=Nqu(A/m)KKNK：chargecarriersperunitvolumeΔI=JΔ⋅SKKu：velocityI=∫J⋅Sd(A)SKKΔI：thetimerateofchangeofcharge

3、J=ρuΔQKρ=Nq：freechargeperunitvolumeΔI==Nqu⋅aˆΔSnKΔtKJ：convectioncurrentdensity=NquΔ⋅SEx：5-1KCathodeEfield:Kdyφ()d⎛12⎞dφ(y)Ey(0==)aEˆˆyy()0=−ay=0⎜mu⎟=edydy⎝2⎠dySteadystate:12K⇒mu=eφatJa=−ˆˆyyJay=ρρ()()uy[:∵Negativenumber]2KK2eφ⎧u()0=0NewtonslawF'=mau=⎨m⎩φ()0=0d

4、uy()dφ()yme=−E()y=eA()dydy−−3119mke=×9.1110()g;−eC=−×1.610(oul)dududydud⎛⎞12m===mmu⎜⎟mudtdydtdydy⎝⎠2u(A)K2ρDetermineφ()y,mustfindPoisson’sEquation∇φ=−ε011Jm−43J⎛m⎞4ρ=−=−Jφ2V4=2⎜⎟d0u2e3ε0⎝2e⎠213dφρJm−4ε02e⎛A⎞2⇒J=V2⎜⎟2=−=φ202dyεε2e9dm⎝m⎠003dφJαV2:Bothsidesmultip

5、liedby20dychild–langmuirlaw21⎛dφ⎞4Jm⎜⎟2C⎜⎟=φ+⎝dy⎠ε02edφy=,0φ=0=0⇒C=0dy11−J⎛m⎞44d2φφ=⎜⎟dyε0⎝2e⎠Leftside：φ=0toV0Rightside：y=0tod*Manycarrier(e、p、ion…)KKAmpÇSemiconductor(electronsandholes)J=∑Niqiui(2)imσ=−ρeμe+ρhμhÅMetallicconductor⎧μ=.038KKe2uE(m)μe>>μh:Ge:⎨m=−

6、μeμ=.018sec⎩hV⋅sec2⎧μ=.012⎛m⎞eμ:electronmobility⎜⎟Si:⎨e⎜⎟μ=.003⎝V⋅sec⎠⎩h2Cu:2.310−3⎛⎜m⎞⎟KKμ=×e⎜⎟[pointform]of⎝V⋅sec⎠J=σE2ohm’slaw−4⎛m⎞Al:μ=4.1×10⎜⎟e⎜⎟⎝V⋅sec⎠Circuitry:ohm’slaw2−3⎛m⎞Agμ=2.5×10⎜⎟e⎜⎟VR=RI⎝V⋅sec⎠KKKJ=ρu=−ρμEeeeK⎛Amp⎞=σE⎜⎟2⎝m⎠σ=−ρμ:conduictivityeeP

7、ointformohm’slawKKJ=σEIV12⎛l⎞=σ⇒V12=⎜⎟IPotentialDifferenceofterminalsSl⎝σS⎠1&2islV=RI⇒R=12V=E⋅lσS12Vl:lengthE=12lS:cross-sectionKKI=∫J⋅dS=JSPointformohm’slawKKSderiveJE=σIVJ=and12J=σE=σcombineCktohm’slawVR=RISlEx：5-2Sol:a)Cu7(S):σ=8.5×10cum3()()−32−6()2l=10m,S

8、=π10=10πmlR==.549()ΩcuσScub)Al7()S:σ=.354×10AlmlR==.899()ΩAlσSAlConductance(G)b)ParallelG=1=S()()Soror(Ω−1)111σ=+RRRRR1112Circuitrya)SeriesG=G+G1112R=R+RSr125-3ElectromotiveForce&K