Question

Light travels more quickly through water than through glass
(a). Which is optically denser: water or glass
(b)If a ray of light passes from glass into water ,which way will it bend: towards the normal or away from the normal

Answer 1

Hint : Light travels faster in a rarer medium than in denser medium. When light travels from denser medium to rarer medium it bends away from the normal and when it travels from rarer medium to denser medium it bends towards the normal. An optically denser medium has more refractive index and an optically rarer medium has less refractive index.

Complete step-by-step solution:
a) An optically denser medium is one in which the velocity of light decreases and refractive index increases and an optically rarer medium is one, in which the velocity of light increases and the refractive index decreases. So it means that refractive index and velocity are inversely proportional to each other. Refractive index of water is $1.33$ and the refractive index of glass is$1.5$. So the refractive index of water is less as compared to glass. Therefore the light travels faster in optically rarer medium and slower in optically denser medium and it also causes change in the direction of light. Since light travels faster in water, glass will be optically denser than water.
b) The phenomenon of bending of light is based on refraction through a medium. Glass is an optically denser medium whereas water is an optically rarer medium. Refractive index of glass is more as compared to water. When light travels in a medium of more refractive index it bends towards the normal as refractive index increases and when it travels into a medium of less refractive index then it bends away from the normal as refractive index decreases. Since water is an optically rarer medium than glass, the light will bend away from the normal when it travels from glass to water, as refractive index is decreasing.
So we can conclude that in the first case Glass is optically denser medium and in the second case when light rays pass from glass to water then it bends away from normal.

Note: Angle of refraction becomes greater than angle of incidence when light travels from denser medium to rarer medium and angle of refraction is less than angle of incidence when light travels from rarer medium to denser medium. Also if the ray of light hits perpendicularly on any surface it will not bend in any direction.