21.1 Introduction
Maxwell's theory predicts the existence of specific electromagnetic fields, known as electromagnetic rates. These fields, once created by time-varying currents and charges, continue to move with a finite velocity independent of the sources that produced them. Much of the rest of this book is devoted to the analysis of various types of elec- tromagnetic waves. In this chapter the simplest type of wave known as a uniform plane time, is considered. Although they are the simplest, uniform plane waves are of extreme practical importance actual waves radiating from sources are sph but at large from sources they become practically plane waves, and in addition, more complicated wave types can be represented as a superposition of plane waves.