If the speed of light in air is represented by e and the speed in a medium is u, then the refractive index of the medium can be calculated using the formula_______.

The refractive index of a medium is defined as the ratio of the speed of light in a reference medium (usually vacuum or air) to the speed of light in the specific medium being measured [2]. According to the provided context, the speed of light in air is marginally less than in a vacuum, and for practical purposes, the refractive index is calculated by dividing the velocity of light in air or vacuum by its velocity in the material medium [3]. In this specific question, the speed of light in air is represented by 'e' and the speed in the medium is 'u'. Therefore, the refractive index (n) is given by the formula n = e/u. This ratio is a dimensionless quantity that indicates how much the light slows down and bends when entering the medium.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.2 The Refractive Index > p. 148
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > What you have learnt > p. 159
3. [3] https://www.britannica.com/science/refractive-index