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.
Information supplied by: http://csep10.phys.utk.edu