Chapter 13 Maxwell s Equation 麦克斯韦方程组 )) (a)沿块球表面传播的地波 2) (b)沿空问直射或经地球反射 (c)沿空经电离层反射或新射 传播的空问波 传播的空问波 图Z1001无线电波传播方式示意图 天线 降体组成。每种光只危由相 的电于 测图 电子枪
Chapter 13 Maxwell’s Equation 麦克斯韦方程组
8 13-1 Displacement Current 位移电流全电流定律 §13-2 Maxwel' s Equation 麦克斯韦方程组的积分形式 Electric Magnetic field Vave's motion
§ 13-2 Maxwell’s Equation 麦克斯韦方程组的积分形式 § 13-1 Displacement Current 位移电流 全电流定律
教学要求 1.理解位移电流及全电流定律; 2.理解麦克斯韦方程组的积分形式; 能总结电磁场理论的基本概念
1. 理解位移电流及全电流定律； 2. 理解麦克斯韦方程组的积分形式； 能总结电磁场理论的基本概念。 教学要求
8 13-1 Displacement Current 位移电流全电流定律 1.Question--Maxwell,'s hypothesis Varying B B E Inducing Varying E °B Inducing?
1.Question—Maxwell’s hypothesis:: B B Varying Inducing E E Varying Inducing? §13-1 Displacement Current 位移电流 全电流定律 E B
James Clerk Can a changing Maxwell electric flux induce considered a magnetic field? certainly!! Displacement Current (varying electric field) The displacement current(位移电流) will set up a magnetic field in exactly the same way as ordinary conduction current 麦克斯韦对电磁场理论的重大贡献的核心是: 位移电流假说
Can a changing electric flux induce a magnetic field? Displacement Current (varying electric field) The displacement current(位移电流） will set up a magnetic field in exactly the same way as ordinary conduction current. 麦克斯韦对电磁场理论的重大贡献的核心是： 位移电流假说 James Clerk Maxwell considered: certainly!!
2 Displacement Current位移电流 As an example of this sort of induction, we consider the charging of a parallelplate capacitor (平行板电容器) with circular plates(very large)as shown in the following figure. Electric field Magnetic field Varving!!
Magnetic field 2. Displacement Current 位移电流 I R As an example of this sort of induction, we consider the charging of a parallelplate capacitor （平行板电容器） with circular plates(very large) as shown in the following figure. Varying!! Electric field
For the loop l: 乐HF·a= To the surface si, we have I·d=l To the surface S,, we have( Contradiction(矛盾) I·d=0 Ampere' s law is invalid(无效 的) for the varying electromagnetic field
H dl ? L = For the loop L: To the surface S1 , we have H dl I L = L S1 S2 I To the surface S2 , we have = 0 L H dl Contradiction (矛盾） Ampere’s law is invalid(无效 的 )for the varying electromagnetic field
Introducing the displacement current Id d d D t ∫D.ds=∫ ds dt dt s at D
S Introducing the displacement current Id : = = = S D d dS t D D S dt d t Φ I S d d d D
Ampere's law is modified(修改)as H d=u+ OpD t Displacement current d L S
L S1 S2 I Displacement current Id t Φ H dl I D L = + 传 Ampere’s law is modified(修改） as
For the surface S+S2, we have d D d dt D·dS+ D·d at at =0+ S d2 According to Gauss's law: 手:4=q() (对本例,在数值上) we have d④ OD dq(t) d 2 d(1+2) ds dt at dt 传
For the surface S1+S2 , we have + = = S S D d D dS dt d t Φ I d d According to Gauss’s law: D dS q(t ) S S = + I 传 dt dq(t ) S t D t Φ I I D d d ( ) = = = = = = + d d d (对本例，在数值上） q(t) L S1 S2 I = + S S D dS dt d D dS dt d = + d I we have