Intensity, Energy Density, the Poynting Vector, and Their Spectral Distributions

Abstract

In the previous chapter a quantity called “intensity of radiation” was introduced when deducing expressions for the scattering cross section. In Eq. (4.12), for example, we introduced the intensity I = E ₀ ²/µ _o c appropriate to a plane monochromatic wave; it is the power flux through unit area placed perpendicular to the propagation direction of the wave. (This quantity is more properly called the irradiance, but we shall use here the more common description.)