22.9 Electromagnetic Waves (continued)

Maxwell's Equations, using values for ordinary electric and magnetic properties that are easily measured in the laboratory, predicted the speed of this electromagnetic wave in vacuum, labeled as c, to be
c =

eo and µo describe the electrical and magnetic characteristics of a vacuum -- or free space.

For vacuum, their values give a speed of 3.00 x 108 m/s for the electromagnetic wave. This is so close to the measured speed of light that it could not be considered a mere coincidence. Further investigation showed light to be an electromagnetic wave; light is a moving disturbance of electric and magnetic fields.

EM waves, like all others, may be described in terms of wavelength or in terms of frequency. Radio waves and infra-red radiation are EM waves with wavelengths longer than light. X-rays and ultra-violet radiation are EM waves with shorter wavelengths. EM waves with still shorter wavelengths are known as gamma rays. The figure below illustrates the wide range of wavelengths or frequencies available in EM waves. Such a description is called the EM spectrum. All are electromagnetic waves. Due to the enormous variation in wavelength, waves with different labels are produced and detected by very different means.

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(c) Doug Davis, 2002; all rights reserved