Question

State the definition of refractive index, absolute refractive index and relative refractive index.

Answer 1

Hint: Learn about refraction of light and refraction of light for different types of mediums. Laws of refraction, how does light bend for different types of mediums and refractive index of any medium.

Formula used:
Refractive index of a material is defined as the ratio of the velocity of light in vacuum to the velocity of light in that medium.
\[n = \dfrac{c}{v}\]
where,\[n\] is the absolute refractive index, \[c\] is the velocity of light in vacuum and \[v\] is the velocity of light in that medium.

Complete step by step answer:
We know that when a light wave travels from one medium to another medium it bends.Laws of refraction states that the incident ray, reflected ray and the normal, to the interface of any two given mediums; all lie in the same plane. Second law of refraction states that, the ratio of the sine of the angle of incidence and the sine of the angle of refraction is constant.

This constant is seen to be the ratio of the absolute refractive index of the two mediums or the ratio of the speed of light in the respective mediums. So, whenever a light ray changes medium the velocity of it changes, as an effect to this the light bends towards the normal or away from the normal, drawn on the point of incidence depending on the mediums which the light travels through.

Refractive index is the measure of this bend of light when it changes a medium, the more the value of the refractive index the more it bends. So, the definition of refractive index of a medium can be given as:
The refractive index of any substance is a dimensionless number which describes how fast light travels through the material with respect to vacuum or any other medium. It measures how much a light ray bends when passing from one medium to another.

Absolute refractive index: The absolute refractive index of a material is defined as the ratio of the velocity of the light when travelling in the vacuum with the velocity of the light ray in that medium.
\[n = \dfrac{c}{v}\]
Where, \[n\] is the absolute refractive index, \[c\] is the velocity of light in vacuum and \[v\] is the velocity of light in that medium.

Relative refractive index: The relative refractive index of a medium with respect to another medium is the ratio of velocity of light in the first medium to the velocity of light in the second medium.It is given by,
\[{}_1{n_2} = \dfrac{{{v_1}}}{{{v_2}}}\]
where \[{}_1{n_2}\] is the relative refractive index of second medium with respect to the first medium, \[{v_1}\] is the velocity of light in first medium and \[{v_2}\] is the velocity of light in the second medium.

Note: Relative refractive index of any medium can also be written in terms of absolute refractive index. It is given by, \[{}_1{n_2} = \dfrac{{{n_2}}}{{{n_1}}}\] where, \[{}_1{n_2}\] is the relative refractive index of first medium with respect to the second medium \[{n_2}\] is the absolute refractive index of the second medium and \[{n_1}\] is the absolute refractive index of the first medium.