Electromagnetic Radiation Explained

In 1864, James Clerk Maxwell set up a series of mathematical equations to provide a general statement of the relationships between electric and magnetic fields under any and all conditions. In balancing this series of equations to achieve mathematical symmetry, he was led to some very interesting conclusions. The equations seemed to indicate that the hitherto existing assumption that all of the energy contained in the electric and magnetic fields accompanying the flow of current in a conductor returned into the conductor when the source of emf was cut off was not wholly true. Some part of the field, it appeared, would detach itself entirely and escape into space in the form of electromagnetic radiation, carrying with it a comparable part of the total energy.

This led to the further conclusion that a moving electric field can exist in the absence of any electric charges, despite the fact that an electric field is usually thought of as being made up of lines of electric force always terminating on electric charges. Furthermore, if a moving electric field can exist independently in space, it must be thought of as being equivalent in certain ways to a flow of electric current. In other words, the moving electric field in free space must set up, or be accompanied by, a moving magnetic field just as it would be in the case of current flow along conductors.

With respect to radiation, the Maxwell equations indicate, and experience confirms, that for a given current the amount of energy radiated depends upon the square of the frequency. Naturally, the amount of radiation also depends upon the intensity of the current. What is of major significance from a practical viewpoint is the fact that the amount of radiation goes up very rapidly as the frequency increases.

It was not until some twenty years after Maxwell developed his famous equations that Heinrich Hertz demonstrated experimentally the truth of the electromagnetic radiation hypothesis; and it was some years later before experimenters began to develop methods for taking advantage of this radiation phenomenon to transmit electric energy through space for useful purposes.

Back to page 1 with a more mathematical development.