Fresnel number

English

Etymology

Named after the physicist Template:W.

Noun

1. Template:Lb A dimensionless quantity (denoted $F$), such that for an electromagnetic wave passing through an aperture and hitting a screen, $F=\frac{a^2}{L\lambda }$ where $a$ is the characteristic size (e.g. radius) of the aperture, $L$ is the distance of the screen from the aperture, and $\lambda$ is the incident wavelength.