Refractive Index

The ratio of the speed of light in a medium relative to its speed in a vacuum is known as the refractive index. This change in speed from one medium to another is known as the refractive index. This is because when light travels in medium other than the vacuum, the atoms of that medium constantly absorb and reemit the particles of light, slowing down the speed light travels at. In this article, let us discuss the refractive index in detail.

What Is Refractive Index?

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. Optical density is the tendency of the atoms in a material to restore the absorbed electromagnetic energy. The more optically dense material is, the slower the speed of light. One such indicator of the optical density of a medium is the refractive index. Before we look at the relationship between the two, let us first understand what refractive index is.

How can we calculate refractive index?

Refractive index is dimensionless. It is a number that indicates the number of times slower that a light wave would be in a material than it is in a vacuum. Refractive index, represented by symbol n, is the velocity of light in vacuum divided by the velocity of light in a medium. The formula of refractive index is given as follows:

n=c/v (1)

where

n is the refractive index

c is the velocity of light in vacuum ( 3 × 108 m/s)

v is the velocity of light in a substance

The vacuum has a refractive index of 1. The refractive index of other materials can be calculated using equation (1). Higher the refractive index, higher the optical density and slower the speed of light. The table below lists the refractive index of different media.

Material

Refractive Index

Air

1.0003

Water

1.333

Diamond

2.417

Ice

1.31
Ethyl Alcohol

1.36

Example of refractive index

The refractive index of glass ng is 1.52 and that of water nw is 1.33. Since the refractive index of glass is higher than the water, the speed of light in water is faster than the speed of light in glass. If the refractive index of a medium is greater than that of another, then the first medium is said to be optically denser. Most of the substances we know have a positive refractive index having value more than zero. Substances with negative permittivity and permeability have a refractive index of negative value.

The refractive index provides a measure of the relative speed of light in different media. Knowing the refractive indices of different media helps the student to identify the direction in which way the light would bend while passing from one medium to another.

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Frequently Asked Questions on Refractive Index

What is refractive index?

Refractive index is the measure of bending of a light ray when passing from one medium to another. It can also be defined as the ratio of the velocity of a light ray in an empty space to the velocity of light in a substance, n = c/v.

What is the formula to calculate the refractive index of a medium?

The refractive index of a medium can be calculated using the following formula:

n = c/v

where n is the refractive index of the medium

c is the velocity of light in vacuum

v is the velocity of light in the medium

Is the speed of light faster in glass or water?

The speed of light is faster in water. The refractive index of water is 1.3 and the refractive index of glass is 1.5. From the equation n = c/v, we know that the refractive index of a medium is inversely proportional to the velocity of light in that medium. Hence, light travels faster in water.

What is the refractive index of the medium in which the speed of light is 1.5 × 108 m/s?

The refractive index of the medium can be calculated using the formula:

n = c/v

Substituting the values in the equation, we get

n = 3 × 108 m/s/1.5 × 108 m/s = 2

The refractive index of the medium is 2.

The speed of light in an unknown medium is 1.76 × 108 m/s. Calculate the refractive index of the medium.

The refractive index of a medium is calculated by the formula:

n = c/v

where c is the speed of light in vacuum

v is the speed of light in the medium

Substituting the values in the above equation, we get

n = (3 × 108)/(1.76 × 108) = 1.7045

Stay tuned to Byju’s to know more about Refraction. To know more about laws of refraction and refractive index you can register to BYJU’s or download our app for simple and exciting content.

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