# Optical physics and principle of reversibility [duplicate]

I know that if a ray is incident at the medium boundary at critical angle, the ray after refraction moves towards the medium boundary. So, is it possible that if a ray is passed through the medium boundary, it will deviate towards the denser medium? if not then can it be called an exception of principle of reversibility of light rays. Please help me through this paradox.

• no thats not what i am saying – Avnish Singh Apr 18 '18 at 18:30
• we all know the principle of reversibility of path of light – Avnish Singh Apr 18 '18 at 18:30
• so when a light ray is incident at a point at angle equal to critical angle it grazes the surface – Avnish Singh Apr 18 '18 at 18:31
• so i am just asking that by the principle of reversibility can we reverse the path i.e will a ray grazing the surface move towards the denser medium at that very point – Avnish Singh Apr 18 '18 at 18:32
• or this is an possible exception – Avnish Singh Apr 18 '18 at 18:33