What is meant by Refractive Index?

Hint: Refractive index is also referred to as refraction index or index of refraction. Refractive index can be defined as the speed of light in vacuum divided by the speed of light in a medium. The speed of light in a medium depends upon the properties of the medium. Higher the refractive index, higher is the density of the medium and slower is the speed of light in that specific material or medium.

Complete answer:
Refractive index can be defined as the ratio of speed of light in vacuum to the speed of light in a medium. Mathematically, refractive index is given by,
$ \mu =\dfrac { c }{ v }$
Where, $\mu$ is the refractive index
             v is the speed of light in a medium
             c is the speed of light in vacuum
Refractive index of various materials can be calculated using the above-mentioned formula. The speed of light depends on the properties of the medium. In case of electromagnetic waves, the speed is dependent on the density of the medium. Greater the density of material or medium, slower is the speed of light. Refractive index helps to measure the speed of light in different media. Refractive index varies with the wavelength of the wave.

Note:
Students must remember that the refractive index is a unitless quantity as it is a ratio of two quantities having same units. The speed of light in vacuum is faster as compared to in air. Students should know the typical refractive indices as sometimes those are not given in the question. Refractive index of water is 1.33, refractive index of air or vacuum is 1 and the refractive index of glass is 1.52.