The Electromagnetic Spectrum

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From http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html from Dept. Physics & Astronomy at the University of Tennessee and http://www.pbs.org/wgbh/aso/tryit/radio/radiorelayer.html from the WGBH Educational Foundation . 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 Wavelength Frequency Energy (Angstroms) (centimeters) (Hz) (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. 1 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. 2 FM vs AM: What's the difference? FM radio works the same way that AM radio works. The difference is in how the carrier wave is modulated, or altered. With AM radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM, the frequency (the number of times each second that the current changes direction) of the carrier signal is varied. FM signals have a great advantage over AM signals. Both signals are susceptible to slight changes in amplitude. With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude don't matter -- since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all. 3.

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