Define Relative Refractive Index

Answer: Relative refractive index refers to the speed of the light when it changes medium. The rate of light’s speed changes as it comes out of a medium and goes inside a medium. This change in the refractive index is known as the relative refractive index. 

How to calculate the relative refractive index: 

To calculate the relative refractive index, we need to know the refractive index of the two mediums through which the light is travelling. Even if you are aware of the speed of light in different mediums, you can calculate the answer. 

Then we can use one of the two given methods to get the answer: 

1. Divide the refractive indexes of both mediums. 
2. Divide the speed of light in both mediums. 

We can write the formula for deriving the refractive index as 

1. either C1/C2, where C denotes the speed of light in mediums 1 and 2, respectively. 
2. Either n1/n2, where n represents the refractive index of the mediums. 

Example of relative refractive index: 

If medium 1 is air with a refractive index of 1.0003 and medium 2 is water with a refractive index of 1.33, the relative refractive index will be equal to 1.0003/1.33 = 0.752 (approx.). 

Difference between absolute refractive index and relative refractive index: 

The absolute Refractive index is derived by dividing the speed of light in vacuum and air, respectively. Thus the two mediums in this case are vacuum and air. The formula used is n= c/v. 

But in the case of a relative refractive index, the mediums can be anything. We try to find the change in the speed of light while travelling in those mediums only and not in vacuum.