An electromagnetic field is a region in space in which electric and magnetic forces interact. A magnetic compass will detect a magnetic field when held close to an electric wire carrying current to a lit lightbulb. The region around the wire has both electrical and magnetic properties and is, therefore, an electromagnetic field.
At one time, scientists thought that electricity and magnetism were totally different forms of energy. The fact that a magnet can pick up certain kinds of materials was thought to have no connection with the flow of electrons through a wire. During the early 1800s, however, experiments began to disprove this view. The movement of electrons and magnetic poles are, as it turned out, closely related to each other.
In the simplest possible case, imagine a single charged particle, such as an electron, traveling through space at a constant speed and in a straight line. The electron creates an electric field around itself. An
electric field is a region in space in which a charged particle is affected. A second electron in the path of the first electron would be deflected by the movement of the first electron, that is, by the electric field created by the first electron.
But the moving electron also generates a magnetic field around itself. The field consists of circular lines of magnetic force around the electron's path. A tiny magnet placed near the electron's path would be twisted in one direction or another by this magnetic field.
The electromagnetic field surrounding the moving electron, then, is some combination of these electric and magnetic fields. That electromagnetic field can be expressed mathematically.
Studying the nature of electromagnetic fields produced by changing electric currents is a more difficult task. The solution to such problems was first devised by English physicist James Clerk Maxwell (1831–1879). Maxwell discovered a set of mathematical equations that can be used to describe the combined electric and magnetic fields produced by a flow of charges.
Maxwell's discovery was one of the great achievements of nineteenth-century physics (the science of matter and energy). It demonstrated that electricity and magnetism are not totally distinct from each other but, instead, are closely related forms of energy. Maxwell's work was the first major step in a long-term effort by physicists to show how all forms of energy are related to each other.
Maxwell's equations are also important because they apply to such a vast range of phenomena. Cosmic rays, X rays, ultraviolet light, infrared radiation, visible light, radar, radio waves, and microwaves may appear to be very different from each other. Yet, they are all forms of energy with which electromagnetic fields are associated. They can all be understood through the use of Maxwell's equations.