How is the refractive index of a medium related to the speed of light ? Obtain an expression for refractive index of a medium with respect to another in terms of speed of light in these two media ?

Explanation

refractive index of a medium `(n)=("velocity of light in vaccum"(c ))/("velocity of light in medium" (v))`
as c is fixed, therefore, `n prop (1)/(v)`. For a rarer medium, n is smaller, therefore v is larger, i.e., light travles faster in a rarer medium than in a denser medium.