北京理工大学电磁场静场1

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,北京理工大学,Beijing Institute of Technology,Static Electric Fields,Field,: a,spatial distribution,of a scalar or vector quantity,Static,: not be a function of,time,Scalar field : for example, altitude field,Vector filed : for example, Electric Field and Magnetic Field,Static Electric Fields:,Postulates of Electrostatics in Free Space,Definition: Electric Field Intensity,Two postulates:,Volume charge density,Static electric field are irrotational,Static Electric Fields:,Postulates of Electrostatics in Free Space,Two postulates in integral form:,Based on Helmholtzs Theorem,A vector field is determined to within an additive constant if both,its divergence,and its,curl,are specified everywhere.,Gausss law,Static Electric Fields:,solution for different charge distribution,+q,For a single point charge,Coulombs Law,Static Electric Fields:,solution for different charge distribution,+q,- q,Derived Coulombs Law,Static Electric Fields:,solution for different charge distribution,q,Static Electric Fields:,solution for different charge distribution,For a system of discrete charges,q,q,1,q,2,q,3,q,4,q,5,q,6,q,7,Vector addition of fields caused by all individual charges,Static Electric Fields:,solution for different charge distribution,Electric dipole,+q,z,o,d,q,Static Electric Fields:,solution for different charge distribution,Electric Field of Electric dipole,Electric dipole moment,Static Electric Fields:,solution for different charge distribution,For a continuous distribution of charges,Charge is distributed on a surface,Charge is distributed alone a line,Static Electric Fields:,solution for different charge distribution,An infinite long ,straight ,line charge,P,z,o,a,0,Ri,Static Electric Fields:,solution for different charge distribution,r,E,a,Electric Field of a spherical cloud of electrons,outside,of spherical cloud:,Ro,Static Electric Fields:,solution for different charge distribution,a,0,Ri,r,E,a,Electric Field of a spherical cloud of electrons,inside,of spherical cloud:,Ro,Static Electric Fields:,electric potential,Base on the identity I :,For static electric field,So electric field can be expressed as the gradient of a scalar field,The scalar field V is called,electric potential,If we know,electric potential, the electric field can be found by gradient operation.,Static Electric Fields:,electric potential,Physical significance of electric potential:,Work,done in carrying a charge from one point to another.,Form Definition of Electric Field Intensity,Static Electric Fields:,Conductors in Static Electric Field,Materials : Conductor, Semiconductor , insulators(or dielectrics),For,Conductors,: the electrons in the outermost shells of atoms,can easily migrate from one atom to another,For,insulators,: the electrons all confined to their orbits.,For,Semiconductors:,they posses a relatively small number of freely movable charges.,Static Electric Fields:,Conductors in Static Electric Field,Inside conductor :,On surface :,Conductor,Free space,d,Conductor/free space boundary conditions,For charged conductor,Static Electric Fields:,Conductors in Static Electric Field,Static Electric Fields:,Dielectrics in Static Electric Field,Nonpolar molecules,Polar molecules,Without external electric field,external electric field,Static Electric Fields:,Dielectrics in Static Electric Field,Definition :Polarization Vector,Volume density of electric dipole moment,Electric dipole moment,E,Static Electric Fields:,Dielectrics in Static Electric Field,Electric dipole moment of an elemental volume,Static Electric Fields:,Dielectrics in Static Electric Field,Static Electric Fields:,Dielectrics in Static Electric Field,Static Electric Fields:,Dielectrics in Static Electric Field,Static Electric Fields:,Dielectrics in Static Electric Field,Gausss law,Static Electric Fields:,Dielectrics in Static Electric Field,