The Electromagnetic
Spectrum

The electromagnetic spectrum is the distribution of electromagnetic radiation according to energy (or equivalently, by virtue of the relations in the previous section, according to frequency or wavelength).

Regions of the Electromagnetic Spectrum

The following table gives approximate wavelengths, frequencies, and energies for selected regions of the electromagnetic spectrum.

Spectrum of Electromagnetic Radiation
Region Wavelength
(Angstroms)
Wavelength
(centimeters)
Frequency
(Hz)
Energy
(eV)
Radio > 109 > 10 < 3 x 109 < 10-5
Microwave 109 - 106 10 - 0.01 3 x 109 - 3 x 1012 10-5 - 0.01
Infrared 106 - 7000 0.01 - 7 x 10-5 3 x 1012 - 4.3 x 1014 0.01 - 2
Visible 7000 - 4000 7 x 10-5 - 4 x 10-5 4.3 x 1014 - 7.5 x 1014 2 - 3
Ultraviolet 4000 - 10 4 x 10-5 - 10-7 7.5 x 1014 - 3 x 1017 3 - 103
X-Rays 10 - 0.1 10-7 - 10-9 3 x 1017 - 3 x 1019 103 - 105
Gamma Rays < 0.1 < 10-9 > 3 x 1019 > 105


The notation "eV" stands for electron-volts, a common unit of energy measure in atomic physics. A graphical representation of the electromagnetic spectrum is shown in the figure below.

The electromagnetic spectrum


Thus we see that visible light and gamma rays and microwaves are really the same things. They are all electromagnetic radiation; they just differ in their wavelengths.

The Spectrum of Visible Light

The visible part of the spectrum may be further subdivided according to color, with red at the long wavelength end and violet at the short wavelength end, as illustrated (schematically) in the following figure.

The visible spectrum


How Roy G. Bv Lost a Vowel

The sequence of colors red, orange, yellow, green, blue, and violet may be remembered by memorizing the name of that fine fellow "ROY G. BV". This was originally "ROY G. BIV", because it used to be common to call the region between blue and violet "indigo". In modern usage, indigo is not usually distinguished as a separate color in the visible spectrum; thus Roy no longer has any vowels in his last name.


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