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The wavelength of a wave is the distance from one crest to the next.
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Wavelength

The wavelength of a wave describes how long the wave is. The distance from one crest to the next, or from one trough to the next, of a wave is its wavelength. Water waves in the ocean, sound waves in air, and light waves of electromagnetic radiation all have wavelengths.

The greek letter "l" (lambda) is often used in equations to represent wavelength. The wavelength of a wave is inversely proportional to the wave's frequency. A long wavelength means a low frequency, while a short wavelength means a high frequency.

Sound waves in the range that humans can hear have wavelengths ranging from less than 2 cm (an inch) to about 17 meters (56 feet). The waves of electromagnetic radiation that make up the visible light that we can see have wavelengths between 400 (purple light) and 700 (red light) nanometers (10-9 meters).

The frequency and wavelength of a wave are related to each other by this equation:

l = c / f

where "l" is the wavelength, "c" is the speed of the wave, and "f" is the frequency. For light or other electromagnetic waves traveling in a vacuum, c = 299,792.458 km/sec (186,282 miles/sec), the speed of light. For sound waves moving through air, c is around 343 meters/second (767 miles/hour).

Red light with a frequency around 440 terahertz has waves about 682 nm long ( l = c / f = 2.99 x 108 m s-1 / 440 x 1012 s-1 = 682 x 10-9 m = 682 nm).

Sound waves with a pitch of 1,000 hertz (1 kHz) produce waves with wavelengths around 34 cm (l = c / f = 343 m s-1 / 1000 s-1 = 0.343 meter).

Last modified August 22, 2006 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA