Question

Predict why the refractive index of air is slightly higher than the refractive index of a vacuum?

Answer 1

Refractive index is also well known as index of refraction. The refractive index is the measure of bending of a light ray when passing from one medium to another. Every material that interacts with light has a refractive index.

Complete step by step answer:
Another definition of refractive index is that it is defined as the ratio of speed of light in vacuum to the speed of light in a particular medium.
So, the formula for refractive index is,
$n = \dfrac{c}{v}$
Where,
$n$ is the refractive index of a particular medium
$c$ is the speed of light in vacuum
$v$ is the speed of light in a particular medium
In the case of vacuum, the speed of light in the medium $v$ is equal to the speed of light in vacuum $c$(as the medium is vacuum), i.e.,
$v = c$
So, $n = \dfrac{c}{c}$
$n = 1........(1)$
But if the medium is air, then, as we know that the light travels slower in the air as compared to vacuum.
So, $0 < v < c$
$n = \dfrac{c}{v} > 1$
$n > 1.........(2)$
Hence, from equation (1) and equation (2), the value of refractive index in air is higher than the value of refractive index in vacuum.

Additional information: The practical use of refractive index is that it is used to determine the sugar content. It is further used to determine the focusing power of lenses, and the dispersive power of prisms.

Note: Refractive index is a unitless quantity. This is because refractive index is defined as the ratio of speed of light in vacuum to the speed of light in a particular medium. We know that the unit of the ratio of two quantities with similar dimensions is unitless.