Electromagnetic spectrum

Electromagnetic spectrum

The varieties of electromagnetic radiation form a continuum known as the Electromagnetic Spectrum. Its broad categories are called

Radio waves

microwaves

infrared light

visible light

ultraviolet light

X-rays

gamma rays

The only difference between these manifestions of electromagnetic radiation is due to differences in the frequency and wavelength of the oscillations. These two quantities are related by the formula
(velocity) = (frequency) x (wavelength), which in this case reads c = f l.

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 Region Wavelength range (approx.) Frequency range (approx.) Comments 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. Electromagnetic waves index examples Lecture index

Region	Wavelength range (approx.)	Frequency range (approx.)	Comments
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.