FLUCTUATING FIELDS

A fluctuating current in a wire or a variable charge gradient between two nearby objects gives rise to a magnetic field and an electrical field in combination. These fields leapfrog through space so that the EM field can travel long distances with less attenuation than either an electrical field or a magnetic field alone. The electrical and magnetic fields in such a situation are perpendicular to each other everywhere in space. The direction of travel of the resulting EM field is perpendicular to both the electrical and magnetic lines of flux, as shown in Fig. 1.

Fig. 1. An EM wave is comprised of fluctuating, mutually perpendicular electrical and magnetic lines of flux. The field travels perpendicular to both sets of flux lines.

In order for an EM field to exist, the electrons in a wire or other conductor not only must be set in motion, but they also must be accelerated. That is, their velocity must be made to change. The most common method of creating this sort of situation is the introduction of an alternating current (ac) in an electrical conductor. It also can result from the bending of charged-particle beams by electrical or magnetic fields.