Optically Dense and Rare Medium

Light travels at different speeds through different types of medium (see Table 14.1). The one in which light travels slower is called an optically dense medium; otherwise, it is an optically rare medium.

From Optically Dense Medium to Rare One

Consider a light ray that enters from an optically dense medium to an optically rare one. The angle of refraction is larger than the angle of incidence. When the angle of incidence gradually increases, the angle of refraction increases more, and the refracted ray becomes closer and closer to the boundary surface.