84 Electromagnetic Radiation/Radio Waves
In 1860 he turned his attention to early electrical work by Michael Faraday. Faraday
invented the electric motor by discovering that a spinning metal disk in a magnetic field created an electric current and that a changing electric current also changed a magnetic field
and could create physical motion.
Maxwell decided to mathematically explore the relationship between electricity and
magnetism and the “electrical and magnetic lines of force” that Faraday had discovered.
As Maxwell searched for mathematical relationships between various aspects of electricity and magnetism, he devised experiments to test and confirm each of his results. By 1864 he
had derived four simple equations that described the behavior of electrical and magnetic fields
and their interrelated nature. Oscillating (changing) electrical fields (ones whose electrical current rapidly shifted back and forth) produced magnetic fields and vice versa.
The two types of energy were integrally connected. Maxwell realized that electricity and
magnetism were simply two expressions of a single energy stream and named it electromagnetic energy. When he first published these equations and his discoveries in an 1864 article,
physicists instantly recognized the incredible value and meaning of Maxwell’s four equations.
Maxwell continued to work with his set of equations and realized that—as long as the
electrical source oscillated at a high enough frequency—the electromagnetic energy waves
it created could and would fly through the open air—without conducting wires to travel
along. This was the first prediction of radio waves.
He calculated the speed at which these electromagnetic waves would travel and found
that it matched the best calculations (at that time) of the speed of light. From this, Maxwell
realized that light itself was just another form of electromagnetic radiation. Because electrically charged currents can oscillate at any frequency, Maxwell realized that light was only a
tiny part of a vast and continuous spectrum of electromagnetic radiation.
Maxwell predicted that other forms of electromagnetic radiation along other parts of
this spectrum would be found. As he predicted, X-rays were discovered in 1896 by Wilhelm
Roentgen. Eight years before that discovery, Heinrich Hertz conducted experiments following Maxwell’s equations to see if he could cause electromagnetic radiation to fly
through the air (transmit through space in the form of waves of energy). He easily created
and detected the world’s first radio waves, confirming Maxwell’s equations and
predictions.
Fun Facts: Astronomers have concluded that the most efficient way of
making contact with an intelligent civilization orbiting another star is to use
radio waves. However, there are many natural processes in the universe that
produce radio waves. If we could translate those naturally produced radio
waves into sound, they would sound like static we hear on a radio. In the
search for intelligent life, astronomers use modern computers to distinguish
between a “signal” (possible message) and the “noise” (static).