How do we say a medium to be rarer or denser? Give two reasons.
A medium can be classified as rarer or denser by following ways.
Rarer medium has less refractive index ex-water (1.33) while denser medium has higher refractive index ex-diamond (2.42).
When light goes from rarer medium to denser medium it bends towards the normal but when light goes from denser to rarer medium it goes away from the normal.