what is rarer medium and denser medium??????????????????

Hi Kalyan

Rarer medium:- If the light travels faster in the second medium, then this medium is called the rarer medium.

Rarer and denser medium refers to the comparison between the densty of various mediums through which a beam of light passes.

For eg. air is much less dense than glass, so glass is a denser medium whereas air is a rarer one. Light always bends towards the normal when passing form a rarer to denser medium i.e. in simpler words, a dense medium slows down light's speed, so it tries to cover the same distance(d) it would have in covered in air in time (say t)
also in the glass medium and thus bends towards the perpendicular to shorten the distance. And vice versa is also true.