Electromagnetic spectrum
The varieties of electromagnetic radiation form a continuum known as the Electromagnetic Spectrum. Its broad categories are called
The types of electromagnetic radiation are listed above in decreasing order of wavelength, and hence increasing order of frequency. (When we study a little quantum mechanics later in the course, we will learn that this is also the order of increasing energy for the individual photons.)
Comments on Regions of the Electromagnetic Spectrum -- adapted from http://calspace.ucsd.edu/ames144a/ch7/ch7.html
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Long-wave radio |
>10 m |
<3x107 hz | Includes traditional AM radio region. These frequencies can travel long distances by multiple reflections between the surface of the earth and its ionosphere. |
Short-wave radio | 10 cm - 10 m | 3x107 - 3x109 | Used for TV, FM, and other communication purposes. Generally travels only relatively short distances because the ionosphere is transparent to it. |
Microwave | 1 mm - 10 cm | 3x109 - 3x1011 | Present limit of radio technology for most purposes. |
Far infrared | 30 mm - 1 mm | 3x1011 - 1013 | 3 K radiation fills universe. |
Thermal infrared | 3 mm - 30 mm | 1013 - 1014 | Thermal emission of earth and planets. |
Near infrared | 700 nm - 3mm | 1014 - 4x1014 | Solar and stellar emission. |
Visible | 400 nm
- 700nm
(1.7 - 3 eV) |
4x1014 -7x1014 | Peak of solar radiation. Visible to human eye, standard photographic film and CCD video detectors. |
Ultraviolet | 200 nm
- 400nm
(3 - 6 eV) |
7x1014
-
1.5x1015 |
Divided at 300 nm by atmospheric (ozone) cutoff. Appreciable solar flux causes sunburn. |
Vacuum UV (EUV) | 10 nm
- 200 nm
(6 - 120 eV) |
1.5x1015 - 3x1016 | Very strong absorption in matter, hence very difficult to observe. |
X-rays | 120 eV- 100keV | 3x1016 - 3x1019 | Produced by electron beams in X-ray tubes, and by inner atomic transitions. Progressively more penetrating as E increases, up to many centimeters in water. |
g-rays | 100 keV | 3x1019 | Produced by nuclear and other high energy processes. Can penetrate up to meters in water. |