A light ray in passing from water to a medium (a) speeds up (b) slows down. In each case, (i) give one example of the medium, (ii) state whether the refractive index of medium is equal to, less than or greater than the refractive index of water.

As we know that, 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.

(a) (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.

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

(a) (ii) The refractive index of the medium (air) is less than that of water as the speed of refracted ray increases.

(b) (ii) The refractive index of the medium (glass) is more than that of water as the speed of refracted ray decreases.