Question

The speed of light depends:
$A.$ Elasticity of the medium only
$B.$ On inertia of the medium only
$C.$ On elasticity as well as inertia.
$D.$ Neither on elasticity nor on inertia

Answer 1

Hint: We know that the speed of light in the medium depends only on the refractive index of the medium. We will use the concept of absolute refractive index of the medium. Absolute refractive index of any medium is defined as the ratio of speed of light in vacuum or air to that of the medium.
Formula Used:
We are going to use the following given formula in order to solve the problem:-
$\mu =\dfrac{c}{v}$ .

Complete answer:
We know that there are two types of medium, one is called rarer medium and other is called denser medium. Rarer medium is the medium in which speed of light is relatively more and the medium in which the speed of light in relatively less is called denser medium. For example, when a light ray travels from air to water then air is rarer medium and water is denser medium because speed of light is relatively more in air.
Absolute refractive index of any medium is defined as the ratio of speed of light in vacuum or air to that of the medium. Mathematically, it is given as follows:-
$\mu =\dfrac{c}{v}$, where $\mu $ is the absolute refractive index, $c$ is the speed of light in vacuum and $v$ is the speed of light in the medium. The medium which has a lower value of refractive index has greater speed of light. A medium with relatively more speed of light is more elastic and the medium with relatively less speed of light is less elastic in nature. Therefore, we can see that the speed of light depends only on the elasticity of the medium.

Hence, option $(A)$ is correct.

Note:
Elasticity in optics means the presence of forces which tend to restore parts of the medium to its original place or position. We should give our attention towards the fact that the speed of light only depends on the refractive index of the medium. We should also be clear about the fact that we are dealing here with only absolute refractive index.