The refractive index of a certain glass is 1.66. for what incident angle is light reflected

If light is moving inside the glass, it will be reflected when the angle of incidence is above the critical angle of the material, which is given by

where
is the refractive index of air
is the refractive index of this type of glass

If we plug the numbers into the equation, we find

So, light will be reflected inside the glass when the angle is equal or greater than this value.

The duration of a photographic flash is related to an rc time constantly