CBSE Class 12-science Answered

When light travels from a rarer to denser medium it bends towards the normal, the condition for total internal reflection requires the ray to bend away from the normal till 90 degree angle is attained. In the rarer to denser case if the incident ray is at 0 degree ( parallel to normal) the refracted ray is also at 0 that mean it is passing straight through, at 90 degree angle of incident ray there will total internal reflection but then incident ray is actually not passing through rarer medium. Hence it will not be a case of rarer to denser medium refraction.