大学物理双语版奥本汉姆课件ChapConDie.pptVIP

* Chapter 22 Conductor and Dielectrics (电介质) in Electrostatic Field Conductor Capacitance Dielectrics Energy Stored in an Electric Field 22-1. A Charged Isolated Conductor (P473) Conductor: there exist a lot of Free moved charges. Insulator(绝缘体): almost no free moved charges. Semiconductor(半导体): between them. 1. Interaction between electrostatic field and conductor A conductor in uniformly electric field : electrostatic equilibrium (静电平衡状态)导体内部和表面都没有电荷的宏观移动 导体 静电感应 electrostatic field free charges redistributing (electrostatic induction) + + + - - - - - - - - - + + + + + + E=0 P473 2. Condition of electrostatic equilibrium (静电平衡) If it were not, then it would have a component along the conductors surface that would exert forces on surface charges, causing them to move. Electric field ?at and just outside the conductors surface must be perpendicular to that surface (导体表面的电场强度垂直于导体表面). 2 The electric field inside conductor must be zero. 1 导体等势是导体体内电场强度处处为零的必然结果 Proof: Choose two arbitrary points a b in a conductor, The potential of conductor at any point is constant. That is, conductor, inside and its surface, are equipotential (导体是等势体,表面是等势面)(P511). 3 i.e. V = C Another expression of the condition of electrostatic equilibrium 3. Distribution of charges on a conductor under the electrostatic equilibrium (P495) P S Choose an arbitrary G.S. in the internal conductor. From Gauss’ Law, —— there is no net charge in any small volume of internal conductor Charge placed on an isolated conductor will move entirely to the surface of the conductor. None of the excess (过量的,额外的) charge will be found within the conductor (导体内净电荷为零). 1 ?S q=??S E: produced by all charged bodies in the space. ?: related to all charge distribution in the space. —— 空间电场与导体电荷相互作用达到平衡的结果。 The magnitude of the at a location just outside a conductor (导体外表面)is proportional to surface charge density at that location on the conductor. 2 (P494) q0 3 An isolated conductor with a cavity (