### wavenumber

**(ν, spatial frequency)**
(reciprocal of wavelength)

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").
If you viewed the ocean and noticed that at some instant,
over a distance of 10 meters, there were three waves, you
could cite the average wavenumber as 0.3 1/m.
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 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*.

(*EMR,measure,waves*)
**Further reading:**

http://en.wikipedia.org/wiki/Wavenumber

**Referenced by pages:**

detective quantum efficiency (DQE)

frequency

Kolmogorov spectrum

visibility

Index