Angle of incidence and Critical angle

Angle of incidence noun - The angle that a line makes with a line perpendicular to the surface at the point of incidence.

Critical angle and angle of incidence are semantically related. In some cases you can replace phrase "Critical angle" with "Angle of incidence", this phrases are similar.

Critical angle noun - The smallest angle of incidence for which light is totally reflected.

Angle of incidence and critical angle are semantically related. You can use "Angle of incidence" instead a noun phrase "Critical angle".