1、Classical ElectrodynamicsJingbo ZhangHarbin Institute of TechnologyChapter 1Classical ElectrodynamicsSection 3ElectrodynamicsAug 26, 2004Classical ElectrodynamicsReviewIn last two sections, we obtained two set vector partial differential equations for electrostatics and magnetostatics, respectively.

2、 They seam to be the independent theories.Aug 26, 2004Classical Electrodynamics1 Electric Charge Conservation LawElectric charge is conserved and electric current is a transport of electric charge. The electric charge conservation law can be formulated in the equation of continuity, It means that th

3、e time rate of change of electric charge density is balanced by a divergence in the electric current density.Aug 26, 2004Classical Electrodynamics2 Maxwells Displacement CurrentIn magnetostatics, we got the source equation for magnetic field,In the case, we used the condition of stationary currents,

4、However, in general case of non-stationary sources and fields, we must follow the equation of continuity,Aug 26, 2004Classical ElectrodynamicsMaxwells source equation for time-varying fieldThe second term on the right side, is so-called Maxwells displacement current.The real current j(t,x) represent

5、 the density of electric current,including conduction current, polarisation current and magnetisationcurrent.The displacement current behaves like a current in vacuum. It predicts the existence of electromagnetic radiation. Aug 26, 2004Classical ElectrodynamicsSymmetric Discussion III First time bro

6、kenElectrostaticsMagnetostaticsAug 26, 2004Classical Electrodynamics3 Faradays Law of InductionOhms Law and Electromovtive ForceUnder certain physical conditions, and for certain materials, thereis a linear relationship between the current density and electricField,where,is the electric conductivity

7、.The electromotive force is defined byThus, we haveAug 26, 2004Classical ElectrodynamicsFor static electric field is conservative field, the closed line integral for it is vanished.Faradays Law the non-conservation EMF field is produced in a closed circuit if the magnetic flux through this circuit v

8、aries with time.Aug 26, 2004Classical ElectrodynamicsAug 26, 2004Classical Electrodynamics4 Maxwells EquationsMicroscopicMaxwells equations relate and j to the fields. with theinitial and boundary conditions,the four vector partial differentialEquations completely determinethe electric and magnetic fields.In the equations, is the totalelectric charge density, free andinduced charges. And j is the totalelectric currents, i.e. conductioncurrents and atomistic currents. Aug 26, 2004Classical ElectrodynamicsMacroscopicThe microscopic field equtionsprovide a correct classical picturefor fields a