Question

Define the term refractive index of a medium. Can it be less than 1?

Answer 1

The refractive index of the second medium with respect to the first medium is defined as the ratio of the sine of the angle of incidence in the first medium to the sine of the angle of refraction in the second medium. Refractive index of a medium is always greater than 1 (it cannot be less than 1) because the speed of light in any medium is always less than that in a vacuum.