# Lecture1 - Lecture 1 Notes 95.658 Spring 2012...

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Lecture 1 Notes, 95.658, Spring 2012, Electromagnetic Theory II Dr. Christopher S. Baird, UMass Lowell 1. Review Class Policy and Syllabus 2. Overview of Electrodynamic Theories LOW SPEED HIGH SPEED (close to speed of light) BIG SIZES Classical Electrodynamics (includes electrostatics, magnetostatics) Maxwell Equations Relativistic Electrodynamics Covariant Maxwell Equations SMALL SIZES (atomic) Classical Quantum Electrodynamics Schrödinger Equation Relativistic Quantum Electrodynamics Dirac Equation 3. Overview of the Course - Last semester we covered electrostatics, magnetostatics, pseudo-magnetostatics, and an introduction to electrodynamics. - This semester we will study electrodynamics in depth, as well as special relativity and relativistic electrodynamics, which is best handled in covariant form. - In electrodynamics, changing magnetic fields can give rise to electric fields which in turn can give rise to new magnetic fields. This feedback process continues indefinitely and a self-sustaining electromagnetic wave propagates and becomes independent of any electric charges or currents. - Seen from a physical perspective, every electrodynamic system necessarily involves electromagnetic waves, whether created, destroyed or transmitted. - We will therefore focus this semester on: - The interaction of waves with materials (reflection, refraction, dispersion, absorption) - Bounded electromagnetic waves (waveguides, cavities) - The creation of electromagnetic waves (radiation, antennas, etc.) - The interaction of waves with objects (scattering) - Special relativity - In this course, a self-sustaining electrodynamic field will be referred to as a “wave” or as “light”. Although in many contexts the word “light” narrowly refers to visible light, it is used in this course to mean any electromagnetic wave of any frequency (radio waves, microwaves, X-rays, etc.) and even those without well-defined frequencies. - It should be noted that waves that are on the high-frequency end of the spectrum (gamma rays, X- rays, ultraviolet, and often even visible) have such a small wavelength that they are often better described using quantum electrodynamics when interacting with materials.

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3. Review of the Maxwell Equations - The behavior of classical electrodynamic fields are completely described by Maxwell's equations: ∇⋅ D = , ∇⋅ B = 0 ∇× E =− B t , ∇× H = J D t - The free electric charge density ρ gives rise to a diverging electric field D . - The change of the total magnetic field B in time gives rise to a curling total electric field E . - The total magnetic field B is always non-diverging (there are no magnetic charges). - The free electric current density J as well as the change of the electric field D in time give rise to a curling magnetic field H . - These equations cannot be used until the material's response to the electromagnetic fields is
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Lecture1 - Lecture 1 Notes 95.658 Spring 2012...

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