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Diagram illustrating the relationship between the wavenumber and the other properties of harmonic waves. In the physical sciences, the wavenumber (or wave number), also known as repetency, [1] is the spatial frequency of a wave, measured in cycles per unit distance (ordinary wavenumber) or radians per unit distance (angular wavenumber).
This equation is known as the Planck relation. Additionally, using equation f = c/λ, = where E is the photon's energy; λ is the photon's wavelength; c is the speed of light in vacuum; h is the Planck constant; The photon energy at 1 Hz is equal to 6.626 070 15 × 10 −34 J, which is equal to 4.135 667 697 × 10 −15 eV.
Relationship between wavelength, angular wavelength, and other wave properties. A quantity related to the wavelength is the angular wavelength (also known as reduced wavelength), usually symbolized by ƛ ("lambda-bar" or barred lambda). It is equal to the ordinary wavelength reduced by a factor of 2π (ƛ = λ/2π), with SI units of meter per ...
A molecular vibration is a periodic motion of the atoms of a molecule relative to each other, such that the center of mass of the molecule remains unchanged. The typical vibrational frequencies range from less than 10 13 Hz to approximately 10 14 Hz, corresponding to wavenumbers of approximately 300 to 3000 cm −1 and wavelengths of approximately 30 to 3 μm.
Using two formulas from special relativity, one for the relativistic mass energy and one for the relativistic momentum = = = = allows the equations for de Broglie wavelength and frequency to be written as = = = =, where = | | is the velocity, the Lorentz factor, and the speed of light in vacuum.
Each propagates at generally different speeds determined by the important function called the dispersion relation. The use of the explicit form ω ( k ) is standard, since the phase velocity ω / k and the group velocity d ω /d k usually have convenient representations by this function.
In 1890, Rydberg proposed on a formula describing the relation between the wavelengths in spectral lines of alkali metals. [2]: v1:376 He noticed that lines came in series and he found that he could simplify his calculations using the wavenumber (the number of waves occupying the unit length, equal to 1/λ, the inverse of the wavelength) as his unit of measurement.
The name "dispersion relation" originally comes from optics. It is possible to make the effective speed of light dependent on wavelength by making light pass through a material which has a non-constant index of refraction, or by using light in a non-uniform medium such as a waveguide. In this case, the waveform will spread over time, such that ...