Question

why is refractive index of a medium always greater than 1

Answer 1

Because refractive index(n) is nothing but the ratio of speed of light in vacuum(c) to the speed of light in that medium(v). n = c/v ; c is always greater than v . So numerator is always greater than denominator that's why n is always greater and equal to 1.

Answer 2

If it is 1 then there will b no refraction so we can say both the mediums r same