# Complex amplitude of the primary wave

## Description

The Huygens–Fresnel principle is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction.
If a point source located at a point, is vibrating at a frequency f, the disturbance may be described by a complex variable Uo known as the complex amplitude. The disturbance produces a spherical wave with wavelength λ, and wave number k = 2π/λ. The complex amplitude of the primary wave at an arbitrary point located at some distance from the source is related to the distance λ and the wave number k.
(The wavenumber is the spatial frequency of a wave. It is the number of waves that exist over a specified distance). Related formulas

## Variables

 Ur0 Complex amplitude at a distance r0 (dimensionless) U0 Complex amplitude at source (m) e e i Imaginary unit π pi λ Wavelength (m) r0 Distance from the source (m)
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