Can relative refractive index of a medium with respect to another medium be less than unity? If yes, give example.
Refraction Plane Surfaces
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Question

Can relative refractive index of a medium with respect to another medium be less than unity? If yes, give example.

KnowledgeBoat · Accepted Answer

Yes, the relative refractive index can be less than 1 when light travels from a denser medium to a rarer medium.

Refractive index of a medium is given by,

$\text {Refractive index} = \dfrac{\text{Speed of light in air or vacuum}}{\text {Speed of light in that medium}}$

In this case, the speed of light increases. For example, the refractive index of water with respect to glass is less than unity.

Physics