A light ray passes from water to (i) air, and (ii) glass. In each case, state how does the speed of light change?

As we know,

Refractive index of air, μ_a = 1.0003

Refractive index of water, μ_w = 1.33

Refractive index of ordinary glass, μ_g = 1.5

With the help of the above values, we can see that μ_g > μ_w > μ_a

When a ray of light gets refracted from a rarer to a denser medium, the speed of light decreases, while if it is refracted from a denser to a rarer medium, the speed of light increases.

So on the basis of above information, we can say that —

(i) When a ray of light passes from water to air, its speed increases as it is moving from a denser to a rarer medium.

(ii) When a ray of light passes from water to glass, its speed decreases as it is moving from a rarer to a denser medium.