A light ray enters from medium $ A $ to medium $ B $ as shown in the figure. The refractive index of medium $ B $ relative to $ A $ will be-

(a) greater than unity    (b) less than unity    (c) equal to unity    (d) zero
"

The correct answer will be option(a) greater than unity.

Explanation

Refraction is the bending of the light wave. When it enters from a fast medium to a slow medium, it bends towards the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media.

The refractive index is the measurement of the bending of a beam of light as it travels from one medium to another. 

In this case, since ray of light in medium B bends towards the normal, which means medium A is rarer and medium B is denser.

So, the speed of light in a rarer medium, A (v₁) is greater than the speed of light in a denser medium, B(v₂) that is v₁>v₂.

Thus the refractive index of B relative to A, $n=\frac{{v}_{1}}{{v}_{2}}$ 

$\Rightarrow n>1$

So, the refractive index of medium B with respect to medium A is greater than unity.

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Updated on: 10-Oct-2022

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