wavenumber

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:

(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.