ABSTRACT
This chapter begins with acquainting ourselves with the polarization of matter. The fundamental quantity describing how an interstellar grain responds to an electromagnetic wave is the dielectric permeability which relates the polarization of matter to the applied field. The chapter explores the basic equations of electrodynamics and outlines how plane waves travel in an infinite non-conducting medium and in plasma. It summarizes the properties of harmonic oscillators, including the absorption, scattering and emission of light by individual dipoles. The chapter discusses the optical constant from the viewpoint that matter is made of harmonic oscillators. It explains the emission of an accelerated charge, compute how an oscillator is damped by its own radiation and evaluate the cross section for absorption and scattering of a single oscillator. In the harmonic oscillator model, the electrons transfer kinetic energy in collisions to the lattice.
