Basic Concepts in Electromagnetic Radiation

This chapter will not discuss the incompleteness of the classical macroscopic electromagnetic theory. Readers who are interested in this topic may find comprehensive discussions in the literature, such as the books by Barrett T W and Rohrlich F. On the contrary, we confine our discussions within the frame of the Maxwell’s theory and try to give an intuitive interpretation to the relationship between the electromagnetic fields and the electromagnetic sources in free space. The electromagnetic fields are solutions to the Maxwell equations. They are generally characterized by some conserved dynamic quantities, of which the most commonly known ones are the electromagnetic energy, the electromagnetic power, the electromagnetic linear momentum, and the electromagnetic angular momentum. We will give a brief introduction to the fundamental notations, concepts, and principles in the classical electromagnetic theory. Detailed and systematic descriptions about the classical electromagnetic theory can be found in classical books.