A wave's wavenumber (or spatial frequency) is the reciprocal of its wavelength, the number of cycles per unit distance, a convenient quantity in the analysis and modeling of waves including EMR and sound waves. An example unit is 1/cm, which means "number of complete waves in a cm" (or "fraction of a complete wave that spans a cm"). Pattern regarding wave terms:
(the wave period or period being the length of time it takes one cycle of the wave to pass.) 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 to distinguish it.
The angular wavenumber is 2π × the wavenumber.