Figure 3.7 Monthly Sunspot Activity Since 1950

Since the earliest consideration was given to the nature of the electromagnetic field and how it behaves thereʼs been discussion concerning whether the field is made up of some type of particles or whether itʼs actually some kind of wave. Some considerations regarding electromagnetic signal propagation are more consistent with the particle view of energy transmission, while others are more consistent with the wave view. To begin exploring these considerations, itʼs good to start with the most basic (and historically earlier) detailed explanations of the electromagnetic field presented by James Maxwell.

The Electromotive Force

When speaking about electromagnetism there are some fundamental quantities that are considered, calculated, estimated, and measured. When we talk about a transmitter sending some energy out into space weʼre ultimately talking about some electrons that were moving around in the radiating element and a magnetic and electrical field moving outward from the radiator. Electrons are in motion and the resulting electromagnetic field is propagating. The field is ultimately going to do the work of moving the electrons in the receiving antenna.

While itʼs electrons (particles with mass) that are moving in the electrically conducting element of an antenna itʼs an electric and magnetic field (forces without accompanying mass) that move in the field pattern surrounding the antenna. It was Albert Einstein who equated mass and energy. In fact, we can consider the implications of Einsteinʼs work in the context of field propagation. Moving objects with mass have momentum. Isaac Newton pointed out that an object in motion would remain in motion unless acted on by some outside force. He described the quality of momentum. When an objectʼs mass or its velocity is increased it becomes harder to change the velocity or direction of the resulting motion. It turns out those equations considering things without mass (like electromagnetic radiation) can involve something similar to momentum as well, even if the thing thatʼs moving doesnʼt actually have mass. The characteristic thatʼs similar to momentum is called momentum density and it manifests itself with a vector quantity called the vector potential of the field. Thank you Albert.

In the discussions of electrostatics and electromagnetism that follow, only the simplest features will be involved. Armed with some solid basic math and a hint of calculus, the reader should have few problems gleaning insight from the text.

Copyright 2003 - Joseph Bardwell