Question

A light ray passes through a glass slab at an angle from air. The same glass slab is now placed in a tank of water. If the same light ray is now allowed to pass through the glass slab, compare the lateral displacement of the light ray in both the cases.
(Given that $n_{water}=1.33$ and $n_{glass}=1.5$)

Answer 1

Glass has a higher refractive index than air and hence light will travel slower in glass than in air. It will travel $1.5$ times slower in glass than in air.

When a light ray travelling through air enters a glass slab,it gets refracted and bends towards the normal. Now, the direction of the refracted ray changes again when it comes out of the glass slab back into air. Since the ray of light is travelling from denser to rarer medium, it bends away from the normal.

In this case, incident ray and the emergent ray are parallel. The ray gets laterally displaced.

When the glass is placed in water, the relative refractive index of the setup becomes

$n_{\text{gw}}=\frac{n_{glass}}{n_{water}}=\frac{1.5}{1.33}=1.125$

$1<1.125<1.5$

The relative refractive index is greater than 1 but lesser than the refractive index of glass alone. So the lateral displacement will be less than the case for glass alone.