Question

what happens usually when a ray of light falls pn a surface or boundary two media.

Answer 1

So, sine(angle of refraction)* index of refraction of the refractive medium is also equal to 0. Now, index of refraction of the refractive medium cannot be 0, so angle of incidence would be equal to 0. So, we get the result that the light ray will pass without any deviation i.e. at o degrees.

Answer 2

The light reflects back in the same direction as it came.