Chapter 29 Maxwell,s Equations and Electromagnetic Waves Chapter 29 Maxwells Equations and Electromagnetic Waves 1.Displacement Current Ampere-Max'Law 2. Maxwells equation 3. Electromagnetic Waves
Chapter 29 Maxwell’s Equations and Electromagnetic Waves Chapter 29 Maxwell’s Equations and Electromagnetic Waves 1. Displacement Current & Ampere-Max’ Law 2. Maxwell’s Equation 3. Electromagnetic Waves
Chapter 29 Maxwell,s Equations and Electromagnetic Waves New words and expressions displacement current位移电流 the density of displacement current位移电流密度
Chapter 29 Maxwell’s Equations and Electromagnetic Waves New words and expressions displacement current 位移电流 the density of displacement current 位移电流密度
Chapter 29 Maxwell,s Equations and Electromagnetic Waves 麦克斯韦(1831-1879) 英国物理学家.经典电磁理 论的奠基人,气体动理论创 始人之一.他提出了有旋场 和位移电流的概念,建立了 经典电磁理论,并预言了以 光速传播的电磁波的存在 在气体动理论方面,他还提 出了气体分子按速率分布的 统计规律
Chapter 29 Maxwell’s Equations and Electromagnetic Waves 麦克斯韦（1831-1879） 英国物理学家 . 经典电磁理 论的奠基人 , 气体动理论创 始人之一 . 他提出了有旋场 和位移电流的概念 , 建立了 经典电磁理论 , 并预言了以 光速传播的电磁波的存在 . 在气体动理论方面 , 他还提 出了气体分子按速率分布的 统计规律
Chapter 29 Maxwell,s Equations and Electromagnetic Waves 1865年麦克斯韦在总结前人工作的基础 上,提出完整的电磁场理论,他的主要贡献是 提出了“有旋电场”和“位移电流”两个假设, 从而预言了电磁波的存在,并计算出电磁波的 速度(即光速) c=台 (真空中) 1888年赫兹的实验证实了他的预言,麦克 斯韦理论奠定了经典动力学的基础,为无线电 技术和现代电子通讯技术发展开辟了广阔前景
Chapter 29 Maxwell’s Equations and Electromagnetic Waves 1865 年麦克斯韦在总结前人工作的基础 上，提出完整的电磁场理论，他的主要贡献是 提出了“有旋电场”和“位移电流”两个假设， 从而预言了电磁波的存在，并计算出电磁波的 速度（即光速）. 1888 年赫兹的实验证实了他的预言, 麦克 斯韦理论奠定了经典动力学的基础，为无线电 技术和现代电子通讯技术发展开辟了广阔前景. 0 0 1 c = ( 真空中 )
Chapter 29 Maxwell,s Equations and Electromagnetic Waves 29-1 Displacement Current Maxwell Equations 1. Displacement Current(位移电流)(P661-p663): Using Ampere-loop law to S, and s2, 乐d=∑=-d (以L为边做任意曲面S) H·dl ds=/ H·dl ds=0
Chapter 29 Maxwell’s Equations and Electromagnetic Waves 29-1. Displacement Current & Maxwell Equations 1. Displacement Current (位移电流)(P661-p663): Using Ampere-loop law to S1 , and S2 , H l j s I L S = = 1 d d + + + + - - - - I （以 L 为边做任意曲面 S ） H l =I l d = s j ds d d 0 2 = = L S H l j s 1 S 2 S L
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