Question

What happens when a ray of light moves from an optically denser medium to an optically raer medium?

Answer 1

When a ray of light moves from optically denser medium to optically rarer medium it speeds up and bends away from the normal

Answer 2

This phenomenon is followed by the concept of total internal reflection. Optically denser medium has refractive index n greater than the refractive index of optically rarer medium. So, when ray of light moves from denser to rarer medium it will deflect away from the normal and deflected angle will be increased. That deflected angle can be upto 90 degrees. that is explain by snell's law.

see diagram in attachment