1. The refractive index of a medium is defined as the ratio of the speed of light in vacuum or air to the speed of the light in the given medium.
\(\text{Refractive index of the medium (n)} = \frac{\text{Speed of the lightin vacuum or air (c)}}{\text{Speed of the light in the given medium (v)}}\)
2. Since it is a ratio, it does not have any unit.
Thus, the refractive index of a medium is defined as the ratio of the speed of light in vacuum to the speed of the light in the given medium. It has no units.
