Electromagnetic forces

Electromagnetic forces are the forces between electrical charges and currents. Our most direct access to those is when our hand touches a door handle after walking on synthetic carpet, or brushing up against an electrical fence. A more powerful example of electromagnetic forces is the lightning we see during thunderstorms. The electrical force is the force between electri- cal charges. The magnetic force is the force between electrical currents.

Electrons are particles that carry a negative electrical charge. There are other particles too, but electrons are responsible for most of what we need to know about how radio behaves.Let us look at what is happening in a piece of straight wire, in which we push the electrons from one and to the other and back, periodically. At one moment, the top of the wire is negatively charged all the negative electrons are gathered there.

This creates an electric field from plus to minus along the wire. The next moment, the electrons have all been driven to the other side, and the electric field points the other way. As this happens again and again, the electric field vectors (arrows from plus to minus) are leaving the wire, so to speak, and are radiated out into the space around the wire.

What we have just described is known as a dipole (because of the two poles, plus and minus), or more commonly a dipole antenna . This is the simplest form of omnidirectional antenna. The motion of the electric field is commonly referred to as an electromagnetic wave