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,
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:
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
is the Planck constant
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.