It is an important observation that all electromagnetic radiation, radio waves through gamma rays, moves at the same universal speed. This is the speed of light, c = 3 x 10 or 30,000,000,000 centimeters per second. For any such radiation we can write

= c = 3 x 10 cm .

Because the speed of light is constant, if we know either the frequency or the wavelength of electromagnetic radiation we can calculate the other quantity.