Light & Electromagnetic Wave

James Clerk Maxwell enshrined the wave theory when he successfully conjectured a connection between light, electricity, and magnetism. He came up with equations that described the behavior of electric and magnetic fields, and when they were combined they predicted electromagnetic waves. He found that these electromagnetic waves had to travel at a certain speed: approximately 186,000 miles per second, which is the speed of light.

Light is the visible manifestation of a whole spectrum of electromagnetic waves. This includes what we now call AM radio signals (wavelength = 300 yards), FM radio signals (wave length = 3 yards), and microwaves (3 inches). As the wavelengths get shorter (i.e. the frequency of the wave increases), they produce the spectrum of visible light, ranging from red (25 millionths of an inch) to violet (14 millionths of an inch). Even shorter wavelengths produce ultraviolet rays, X-rays, and gamma rays. When we speak of "light" and the "speed of light," we mean all electromagnetic waves, not just the ones that are visible to our eyes.