critical angle

noun

Optics. the minimum angle of incidence beyond which total internal reflection occurs for light traveling from a medium of higher to one of lower index of refraction; the angle of incidence for which refracted rays emerge tangent to the surface separating two media, the light traveling from the medium of higher to the medium of lower index of refraction.

Also called angle of stall, critical angle of attack, stalling angle. Aeronautics. the angle of attack, greater than or equal to the angle of attack for maximum lift, at which there is a sudden change in the airflow around an airfoil with a subsequent decrease in lift and increase in drag.

Origin

1870-75

Examples from the web for critical angle

However, for low energy the channeling critical angle becomes much larger so that the actual situation needs detailed study.
What is measured is the profile of reflectivity as a function of angle beyond the critical angle for total external reflection.
The microstructure that can be seen above the critical angle, the left image, indicates that the sample is strained.
The lower limit is due to the x-ray windows and the upper limit is due to the critical angle of the x-ray mirror.
The speed at which the critical angle of the relative wind is exceeded is the stall speed.

British Dictionary definitions for critical angle

critical angle

noun

the smallest possible angle of incidence for which light rays are totally reflected at an interface between substances of different refractive index

another name for stalling angle

critical angle in Science

critical angle

(krĭt'ĭ-kəl)
The smallest angle of incidence at which radiation, such as light, is completely reflected from the boundary between two media. At angles smaller than the critical angle, some of the radiation enters the second material and is refracted.

Encyclopedia Article for critical angle

in optics, the greatest angle at which a ray of light, travelling in one transparent medium, can strike the boundary between that medium and a second of lower refractive index without being totally reflected within the first medium. (The refractive index of a transparent substance is the ratio of the speed of light in a vacuum to its speed in that substance.) For any angle of incidence smaller than the critical angle, and for any angle at all if the ray strikes the boundary from the other side, part of the beam will penetrate the boundary, being refracted in the process.

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