 A scottish physicist named James Clerk Maxwell showed that electric and magnetic fields fluctuating together can form a propagating wave, which was named an electromagnetic wave. Light is this type of wave

 Maxwell knew that a changing electric field produced a magnetic field. He hypothesized that a changing magnetic field would produce an electric field because most things in nature are balanced. Based on the work of Farady and Hertz, this was discovered to be true.

 A common way to generate an electromagnetic wave is to have an antenna connected to an alternating current which will cause a changing magnetic field which will cause another changing magnetic field and so on. These waves are also produced in stars in the form of UV rays, X rays, and Gamma rays.

 An electromagnetic wave, like other waves, has a frequency f, a speed v and a wavelength, which are related by the equation. In vacuum or in air, to a good approximation, the speed v = c (speed of light: m/s) So the relationship would be

 The photo shows the electromagnetic spectrum, which depicts electromagnetic waves over a huge range, for values less than 104 Hz to those greater than 1022 Hz. Because all of these waves travel at the same speed, this drawing can also be used to figure out the wavelengths. We can also see the grouping of the spectrum into radio waves, infrared, ultraviolet, x and gamma rays. Shown here the boundaries are sharp but in actual practice the boundaries are not so well defined and the regions overlap.

 Beginning on the left are the radio waves. The lower frequency radio waves are generally produced by electric oscillator circuits while the higher frequency waves (microwaves) are generated using electron tubes called klystrons. The next set, called infrared or loosely reffered to as heat waves, generally originate with the vibration and rotation of molecules within a material.