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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>


For radio waves this relationship is easily handled with this formula: meters of wavelength = 300/frequency in megahertz (MHz)

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} {mv} = \frac {h} {m_0v} \sqrt{1 - \frac{v^2}{c^2}}</math>

where h is the Planck constant, m0 is the particle's rest mass, and v is the particle's velocity.

Wavelength is the title of a 1978 album by Van Morrison.

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