Chapter 29 Maxwell,s Equations and Electromagnetic Waves They are contradict. To make them coordinate we need to consider the continuity of current. o dd +o dqd(Sσ)cd S □-dt dt dt dt do dd do D=o D dt dt dt B dd dyp y=SDⅠ=S dt dt 麦克斯韦假设电场中某一点位移电流密度等 于该点电位移矢量对时间的变化率
Chapter 29 Maxwell’s Equations and Electromagnetic Waves They are contradict. To make them coordinate, we need to consider the continuity of current. t S t S t q I d d d d( ) d d c = = = t j d d c = D = t t D d d d d = t Ψ t D I S d d d d Ψ = SD c = = + + + + + - - - - - I t D d d D c j c j − + I B A 麦克斯韦假设 电场中某一点位移电流密度等 于该点电位移矢量对时间的变化率
Chapter 29 Maxwell,s Equations and Electromagnetic Waves ◆ the density of displacement current(位移电流 密度) aD at displacement current C ad dyp ds Js at 通过电场中某一截面的位移电流等于通过该截面 电位移通量对时间的变化率 全电流、=l。+Ja
Chapter 29 Maxwell’s Equations and Electromagnetic Waves t D j = d the density of displacement current (位移电流 密度 ) displacement current t Ψ s t D I j s S S d d d d d d = = = 通过电场中某一截面的位移电流等于通过该截面 电位移通量对时间的变化率. + + + + + - - - - - d I c I 全电流 s c d I = I + I
Chapter 29 Maxwell,s Equations and Electromagnetic Waves So, at non-steady current, Ampere law can be rewritten as: h- dl=l L s I dy aD h. dl as at 1)全电流是连续的; 2)位移电流和传导电流一样激发磁场; 3)传导电流产生焦耳热,位移电流不产生焦耳热
Chapter 29 Maxwell’s Equations and Electromagnetic Waves t Ψ H l I I L d d d = s = c + == + s d ( c ) ds t D H l j L So, at non-steady current, Ampere law can be rewritten as: 1）全电流是连续的； 2）位移电流和传导电流一样激发磁场； 3）传导电流产生焦耳热，位移电流不产生焦耳热
Chapter 29 Maxwell,s Equations and Electromagnetic Waves Explanations: (1) Fictitious displacement current between the plates is associated with that changing E-field (iH 过某个面积的位移电流为通过该面积的电位移通量对时 间的变化率) ddp dopE 二 dt odt (2) The displacement current given by maxwell is, in nature, that a changing electric flux will always induce a magnetic field whenever it occurs
Chapter 29 Maxwell’s Equations and Electromagnetic Waves t t I D E d d d d d 0 = = (1) Fictitious displacement current between the plates is associated with that changing E-field. (通 过某个面积的位移电流为通过该面积的电位移通量对时 间的变化率). Explanations: (2) The displacement current given by Maxwell is, in nature, that a changing electric flux will always induce a magnetic field whenever it occurs
Chapter 29 Maxwell,s Equations and Electromagnetic Waves 3) Although I and ld are equivalent at producing magnetic field, they are different in that displacement current is varying electric field 位移电流是变化的电场,可以存在于一切物质或真空中而 传导电流是导体中电荷的定向运动
Chapter 29 Maxwell’s Equations and Electromagnetic Waves (3) Although I and Id are equivalent at producing magnetic field, they are different in that displacement current is varying electric field. 位移电流是变化的电场,可以存在于一切物质或真空中而 传导电流是导体中电荷的定向运动