Refraction and Dispersion of Light Through A Prism



A ray of white light while travelling obliquely from one medium to another, it is seen to deviate from its original course. Along with that, while passing through a transparent substance like a glass prism, the white light distributes in its constituent spectrum of colours. Based on these two concepts of physics, the tutorial intends to include an effective discussion regarding refraction and dispersion of light through a prism.

What Is The Dispersion of Light?

The phenomenon of dispersion can be defined as the splitting of visible light into its component colours. Light is considered a mixture of different colours which have different wavelengths and similar points of frequency at a singular point. The visibility and wave of white light, in physics, is considerably known as a significant form of electromagnetic waves.

Figure 1: Visible light spectrum

White light gets its visibility when all the spectrums are seen together. Based on these conditions, the human eye can catch all the visible spectrum of light when it incidents on a glass prism (Lefèvre, 2022).

For the reason of having changed speed, the entire spectrum becomes visible as it appears in a multicolour pattern; this particular incident is defined as the dispersion of light.

What Is The Refraction of Light?

The refraction means the incident where a ray of light deviates from its original course. The main reason for refraction is the variation of velocity a ray of light beholds in different mediums.

For example, the light travels slower in a medium, which is dense whereas the speed of light becomes faster in a rarer medium. Two laws of refraction work at this moment,

  • first one states that the refracted and incident rays are in the plane the same as the normal (Bhattacharjee, 2021).

  • The second law states that if the incident ray comes from one medium and falls on the boundary of one medium, while refraction the ratio of the sign angle of incidence and of refraction is constant.

Refraction of Light through a Glass Prism

Figure 2: Refraction of light through a glass prism

A glass prism is visibly beheld 3 rectangular surfaces that are lateral and 2 triangular bases, all inclined at an angle. In the above figure, the D is the angle of the prism. As per the laws of refraction of light, the light bends towards the normal as it travels through a denser medium from a rarer medium and it bends from the normal when the path of travelling becomes denser to a rarer medium (Kapoor, 2021).

The glass is denser in comparison to normal air, therefore the ray JP bends towards normal GP.

Glass Prism-Desperation of Light

Figure 3: Desperation of Light by a glass prism

A prison is recognised as a sphere made of five solid sides with two triangle bases along with rectangular surfaces that are angled inward. The angles of the distinct colours of light bend again as the refraction are induced second time by the second rectangular surface of the prism. The main reason of refraction of light is that a ray of white light has a range array of seven colours.

These seven colours have the subsequent angles of deviation. Among the colours, the deviation of the Red colour is the least and got the position at the top of the series of a band of colours the refraction of white light makes.

In such cases, the violate deviates the most, and for this reason, the colour violet gets the musician at the bottom of the colour band. After entering polychromatic lights into the lens dense medium, it is for the refraction that every colour of light takes a different path.

Examples of Dispersion of Light

The examples of different dispersions of light are as follows:

Dispersion by a prism: The time when white light falls on the surface of a glass prism, a ban of seven different colours is found that comes out from the prism for the dispersion.

Formation of Rainbow: A rainbow is generally known as a multicoloured arch, formed when the ray of sunlight strikes and dispersion of the ray happens by water droplets present in the air (Geeksforgeeks, 2021).

Dispersion in a diamond: As a dense medium in comparison to air, diamond also causes dispersion of light that is also known by the name of diamond fire.


The present tutorial has cast light on the concept of refraction and dispersion of light through a prism, made of glass. Here, it is observed that the light is made of different coloured spectrums which have different wavelengths too. For this reason, when a ray of light travels through a denser substance from rarer, the angle of refraction of light bends and the multicoloured spectrum is formed. In this tutorial, the laws of refraction and examples of dispersion are included.


Q1. Why does dispersion happen from a prism and not through a glass slab?

A scattering of light can be seen in a prism whereas a glass slab works as double prison through which the ray of light passes directly.

Q2. Why rainbow is observed after a rainfall?

After a rainfall, the droplets that are present in the air start to act like a prism that helps to scatter the ray of sunlight into various colours that forms a visually colourful arch.

Q3. What is a prism?

A prism is identified as a solid and transparent body that is made of three rectangular lateral surfaces and two triangular surfaces that are inclined at an angle.

Q4. What is the difference between refraction and reflection of light?

Refraction of light causes a change in the direction f light whereas the reflection can be seen when rays of light bounce off a medium.



Bhattacharjee, P. R. (2021). Discovery of total failure of the traditional laws of reflection and refraction of light to explain the phenomena of reflection and refraction. Optik, 240, 166923. Retrieved from:

Kapoor, S. (2021). Prisms in ophthalmology. Journal of Clinical Ophthalmology and Research, 9(3), 152. Retrieved from:

Lefèvre, H. C. (2022). Comments about dispersion of light waves. Journal of the European Optical Society-Rapid Publications, 18(1), 1. Retrieved from:

Websites, (2021). Dispersion of Light. Retrieved from: [Retrieved on 10th June 2022], (2022). Human eye and colourful world. Retrieved from: [Retrieved on 10th June 2022]

Updated on 13-Oct-2022 11:19:47