Editing Plane wave (section)

===Sinusoidal plane wave===
{{Main|Sinusoidal plane wave}}

The term is also used, even more specifically, to mean a "monochromatic" or [[sinusoidal plane wave]]: a travelling plane wave whose profile <math>G(u)</math> is a [[sinusoidal]] function.  That is,
<math display="block">F(\vec x, t) = A \sin\left(2\pi f (\vec x \cdot \vec n - c t) + \varphi\right)</math>
The parameter <math>A</math>, which may be a scalar or a vector, is called the [[amplitude]] of the wave; the scalar coefficient <math>f</math> is its "spatial frequency"; and the scalar <math>\varphi</math> is its "[[phase shift]]".

A true plane wave cannot physically exist, because it would have to fill all space.  Nevertheless, the plane wave model is important and widely used in physics. The waves emitted by any source with finite extent into a large homogeneous region of space can be well approximated by plane waves when viewed over any part of that region that is sufficiently small compared to its distance from the source.  That is the case, for example, of the [[light wave]]s from a distant star that arrive at a telescope.