Astrophysics (Index)About

wavenumber

(ν, spatial frequency)
(reciprocal of wavelength)

A wave's wavenumber (or spatial frequency) is the reciprocal of its wavelength which is the number of wavelengths per unit distance, a useful quantity in the analysis and modeling of waves such as EMR and sound waves. An example unit is 1/cm, aka cm-1. which means "number of complete waves in a cm" (or "fraction of a complete wave that spans a cm"). If you viewed the ocean and noticed that at some instant, over a distance of 10 meters, there were four waves (for an average wavelength of 2.5 meters), you could cite the average wavenumber as 0.4 m-1. Pattern regarding wave terms:

time space
quantity wave period wavelength
reciprocal frequency wave number

(the wave period or period being the length of time it takes a complete oscillation of the wave to pass some point in space.) Relations between the terms (given compatible base units, e.g., m and 1/m):

 wavelength × wavenumber = 1
 frequency × period = 1
 wavelength × frequency = wave speed
For EMR:
 wavelength × frequency = c

The symbol ν is sometimes used for the wavenumber, but also often for frequency. Sometimes, for wavenumbers, a tilda (~) is placed over ν (i.e., ṽ) to distinguish it.

The angular wavenumber is 2π times the wavenumber.


(EMR,measure,waves)
Further reading:
https://en.wikipedia.org/wiki/Wavenumber
https://www2.chemistry.msu.edu/faculty/harrison/cem483/wavenumbers.pdf
https://www.techtarget.com/whatis/definition/wave-number
https://www.rp-photonics.com/wavenumber.html

Referenced by pages:
detective quantum efficiency (DQE)
frequency (ν)
Kolmogorov spectrum
visibility

Index