Question

Can the absolute value of the refractive index be less than unity?

Answer 1

Refractive index:

1. The Refractive index is also referred to as the refraction index or index of refraction. The speed of light in a medium depends on the properties of the medium. In electromagnetic waves, the speed is dependent on the optical density of the medium.
2. The refractive index is dimensionless. It is a number that indicates the number of times slower than a light wave would be in the material than it is in a vacuum. The refractive index, represented by the symbol $n$, is the velocity of light $\left(c\right)$ in a vacuum divided by the velocity of light in a medium $\left(v\right)$.
3. The formula of the refractive index is as follows:

$n=\frac{c}{v}$

No, if the absolute refractive index is lower than unity. then

1. The speed of light in that medium is faster than in a vacuum, which is impossible.
2. The rate of the speed of light in a vacuum to the speed of light in that medium is the absolute refractive index of that medium.
3. In a vacuum, the speed of light is always faster than in any other medium.
4. The rate of light speed in a vacuum to light speed in any other medium is always larger than one.
5. Any medium's absolute refractive index is always larger than 1.