Wavelength
From Wikinfo
[[de:Wellenl�nge]]
The wavelength is the distance between repeating units of a wave pattern. It is commonly designated by the greek letter lambda (λ).
In a sine wave, the wavelength is the distance between peaks:
The x axis represents distance, and I would be some varying quantity (for instance air pressure for a sound wave or strength of the electric or magnetic field for light), at a given point in time as a function of x.
Wavelength has an inverse relationship frequency, the number of peaks to pass a point in a given time. The wavelength is equal to the speed of the wave divided by the frequency of the wave. When dealing with electromagnetic radiation in a vacuum, this speed is the speed of light c, so the conversion becomes,
- <math>\lambda = \frac{c}{\nu}</math>
where:
- λ = wavelength of an electromagnetic wave
- c = speed of light = 3×108 m/s
- ν = frequency of the wave
For radio waves this relationship is easily handled with this formula: meters of wavelength = 300/frequency in megahertz (MHz)
When light waves (and other electromagnetic waves) enter a medium, their wavelength is reduced by a factor equal to the refractive index n of the medium, but the frequency of the wave is unchanged. The wavelength of the wave in the medium, λ' is given by:
- <math>\lambda^\prime = \frac{\lambda_0}{n}</math>
where λ0 is the vacuum wavelength of the wave. Wavelengths of electromagnetic radiation are usually quoted in terms of the vacuum wavelength, although this is not always explicitly stated.
Louis-Victor de Broglie discovered that all particles with momentum have a wavelength, called the de Broglie wavelength. For a relativistic particle, this wavelength is given by
- <math> \lambda = \frac{h}{p} = \frac {h}{mv} \sqrt{1 - \frac{v^2}{c^2}}</math>
where h is the Planck constant, p is the particle's momentum, m is the particle's mass, and v is the particle's velocity.
See also: frequency, period, amplitude
Wavelength is the title of a 1978 album by Van Morrison.
References
- Adapted from the Wikipedia article, "Wavelength" http://en.wikipedia.org/wiki/Wavelength, used under the GNU Free Documentation License
