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Classical Electrodynamics. Jingbo Zhang Harbin Institute of Technology. Chapter 3 Electromagnetic Potentials. Section 1 Electrodynamic Potentials. Section 2 Gauge Transformations. Review. Field Equations. Fields and Potentials. Potential Equations. 1 Lorentz Gauge. In Lorentz gauge.
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Classical Electrodynamics Jingbo Zhang Harbin Institute of Technology
Chapter 3Electromagnetic Potentials Section 1Electrodynamic Potentials Section 2Gauge Transformations
Review Field Equations Fields and Potentials Potential Equations Classical Electrodynamics
1 Lorentz Gauge In Lorentz gauge uncoupled imhomogeneous wave equations coupled imhomogeneous wave equations Classical Electrodynamics
Introducing d’Alembert operator Lorentz equations for potentials Classical Electrodynamics
Retarded Potentials the solutions of Lorentz potential equations The solutions at time t at field point x are dependent on the behaviour at an early time t’ of the source point x’. Classical Electrodynamics
2 Coulomb Gauge In Coulomb gauge coupled imhomogeneous wave equations Poisson equation and imhomogeneous wave equations Classical Electrodynamics
solution of Poisson equation • solution of imhomogeneous wave equation The scalar potential is only dependent on charge density source at time t. The retardation effects occur only in the vector potential. Classical Electrodynamics
3 Gauge Transformations • Turning the potentials simultaneously into the new one according to the following transformation, where, is an arbitrary differentiable scalar function is called the gauge function. A transformation of the potentials which leaves the fields and Maxwell’s equations invariant is called a gauge transformation. A physical law or quality which doesn’t change under a gauge transformation is said to be gauge invariant. Classical Electrodynamics
Gauge invariant of Lorentz wave equations, If we require the gauge function itself be restricted to fulfill the following equation, such transformation would keep the Lorentz equations invariant. Classical Electrodynamics
Homework 3.2 • (Textbook page 46)Example 3.1 In Dirac’s symmetrised form of electrodynamics, derive the inhomogeneous wave equations with introducing the potentials. Classical Electrodynamics