When a ray of light moving in a medium enters obliquely into another medium, it bends from its path. This phe…

When a ray of light moving in a medium enters obliquely into another medium, it bends from its path. This phenomenon is called refraction of light. The ability of a medium to refract light is also expressed in terms of optical density. It is not the same as mass density. We use the terms ‘rarer medium’ and ‘denser medium’ which actually means ‘optically rarer medium’ and ‘optically denser medium’ respectively. When we say that a medium ‘A’ is optically denser than the other medium ‘B’, we mean that the refractive index of medium A is more than the refractive index of medium ‘B’. The speed of light is higher in a rarer medium than a denser medium. Thus a ray of light travelling from a rarer medium to a denser medium slows down and bends towards the normal.