Question

Write a short note on the refractive index.

Answer 1

Hint: In order to answer this question, first we will explain the refractive index and then we will also represent it numerically in terms of the speed of light and the velocity of light. And then we will also explain whether the refractive index is dimensionless or not.

Complete answer:
The refractive index of a substance (also known as refraction index or index of refraction) is a dimensionless quantity that specifies how fast light passes through it in optics. It's described as:
$n = \dfrac{c}{v}$
where, $c$ is the speed of light in vacuum and, $v$ is the phase velocity of light in the medium.

Water, for example, has a refractive index of 1.333, which means light travels 1.333 times slower in water than in air. When the refractive index of a substance is increased, the speed of light in the material decreases.When white light is refracted, the refractive index varies with wavelength, causing it to break into constituent colours. This is referred to as dispersion.

It can be seen in prisms and rainbows, as well as in lenses as chromatic aberration. A complex-valued refractive index can be used to characterise light propagation in absorbing materials. After that, the imaginary part is in charge of attenuation, while the actual part is in charge of refraction. Across the visible spectrum, the refractive index of most materials changes by several percent with wavelength.

However, refractive indices for materials are frequently reported with a single value for $n$ , which is usually measured at $633\,nm$.The rate of change of refractive index with respect to distance in the material is known as the refractive index gradient. The slope of the refractive index profile at any point is referred to as distance. The reciprocal of a unit of distance is used to express the refractive index gradient.

Note:The slower the speed of light is, the more optically dense the substance is. The refractive index is one such measure of a medium's optical density. The refractive index has no dimensions. It's a number that indicates how much slower a light wave would travel through a substance than it would in a vacuum.