Question

What are the factors that influence refractive index?

Answer 1

Hint : To answer this question, we need to use the basic formula of the refractive index, which relates the speeds of lights in different mediums. Then, on investigating the factors which can vary the speed of light in a particular medium, we can list them.

Formula used: The formula which are used in solving this question are given by
$\Rightarrow \mu = \dfrac{c}{v}$, here $\mu $ is the refractive index of a medium, $c$ is the velocity of light in vacuum, and $v$ is the velocity of light in the medium.
$\Rightarrow v = \lambda \nu $, here $v$ is the speed of a wave having wavelength $\lambda $ and frequency $\nu $.

Complete step by step solution:
We know that the refractive index of a medium is the ratio of the speed of light in vacuum to that in the medium. That is
$\Rightarrow \mu = \dfrac{c}{v}$ ………………….(1)
So, the refractive index is basically a measure of how much the velocity of light deviates from its value in vacuum. Now, as the only variable in the expression for the refractive index is the velocity $v$, so we need to see the factors which affect the speed of light in a medium. These are:
-Nature of medium: By the nature of a medium, we are actually referring to the optical density of that particular medium. We know that the speed of light is inversely proportional to the optical density. Hence, denser is a medium, less is the speed of light, and from (1) we can say more is the refractive index of that medium.
-Temperature: We know that the volume of a substance increases with the increase in temperature. Increase in the volume means the decrease in density. So the photons of light, which describe its motion, find less resistance for their movement in that substance. So, the velocity of light will increase with the increase in temperature. Hence from (1) we can say that the refractive index will decrease with the increase in temperature.
-Wavelength: We know that the light is basically an electromagnetic wave, whose speed is given by $v = \lambda \nu $. Since the frequency is a constant for a given light wave, so the speed of light is proportional to the wavelength of the light used. Hence, increasing the wavelength increases the speed of light, and thereby decreasing the refractive index.

Note:
The refractive index is a useful quantity used in many real life applications. For example, it is used in measuring the concentration of an aqueous solution. The concentration of a drug is measured in the pharmaceutical company with the value of the refractive index. By measuring the concentration, we can also determine the purity of a substance. Also, it is used in the identification of different substances.