critical angle

[ krit-i-kuhl ang-guhl ]

noun

1. 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.
2. Also called angle of stall,. 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.

critical angle

noun

1. the smallest possible angle of incidence for which light rays are totally reflected at an interface between substances of different refractive index
2. See stalling angle
   another name for stalling angle

critical angle

/ krĭt′ĭ-kəl /

1. 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.

Word History and Origins

Origin of critical angle¹

First recorded in 1870–75

Example Sentences

The heavy line indicates what is commonly known as the critical angle.

From Project Gutenberg

The question is, is the critical angle really as high as Mr. Seller's experiments would show.

From Project Gutenberg

When this condition is reached, the angle of incidence is called the critical angle.

From Project Gutenberg

For diamond this critical angle, as it is called, is very nearly 24° from a perpendicular to the surface.

From Project Gutenberg

Glass is made in many varieties, each with a special critical angle, never much different from that of water.

From Project Gutenberg