How Dispersion Works: Causes, Effects & Everyday Examples
Dispersion Physics is the breaking or scattering of something.
From our childhood days, we love to see a rainbow. A rainbow is the dispersion or scattering of seven colours of light and giving a beautiful scenic view of the sky.
So, we know that dispersion Physics plays an important role in our day-to-day life.
Dispersion is a phenomenon that we see in the glass of water and the dispersion of water in the glass is similar to the dispersion of tiny water droplets in the rainbow formation; this article discusses the same in detail.
Define Dispersion of Light
Light refers to what we see or to a piece of the electromagnetic spectrum that operates on the optical telescope, especially on the ground, and sometimes, it means the entire electromagnetic spectrum or any electromagnetic radiation.
When this light gets split into different colour lights having varying wavelengths, it is the dispersion of light. The light that we can see is the visible spectrum, the below image shows the wavelengths of each light in the spectrum in nanometers or nm:
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Dispersion Definition Physics
In Physics, dispersion is the division of white light into seven colours of varying wavelengths and frequencies in the sequence of VIBGYOR.
Wave dispersion is observed in wave motion of light, water. It is a phenomenon associated with the propagation of individual waves at respective speeds that totally depend on their wavelengths.
For instance, ocean waves move at speeds directly proportional to the square root of their wavelengths; these speeds vary from a few feet per second for disturbances/ripples to hundreds of miles per hour for tsunamis.
What Is Dispersion??
From the above text, we understood that dispersion is the scattering of something into small or tiny particles.
The dispersion optics talks about the prism, which is kept still, and the light when passed through breaks or disperses into seven colours, i.e., VIBGYOR.
Here, V is for violet, I is for Indigo, B is for blue, G is for green, Y is for yellow, O is for orange, and R is for red.
Here, we talked more about white light, so do you know what white light is and what is dispersion in Physics?
What is Dispersion in Physics?
The complete blend of all the wavelengths of the visible spectrum is known as white light. This indicates that if a person has a beam of light of the visible spectrum, i.e., all the colours of the rainbow, and focuses all of them onto a single spot, the combination of all colours results in a beam of white light.
White light or visible light has a range above infrared rays. At its peak, the Sun emits visible light. However, combining the entire emission power spectrum passes all wavelengths showing that the Sun emits slightly more amount of infrared rays than visible light.
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Dispersion Optics in Physics
Dispersion Optics is the phenomenon in which the phase velocity of a wave depends on its frequency. Media having dispersion optics characteristics is termed dispersive media. We often use the term chromatic dispersion for generalization.
However, the term dispersion optics in Physics is used in the field of optics to describe light and other electromagnetic waves, it applies to any sort of wave motion like acoustic dispersion of sound, seismic waves, in gravity waves, oceanic waves, and also for telecommunication signals along transmission lines, like a coaxial cable or optical fibre.
Dispersion Optics
To understand what is dispersion optics, let’s perform a simple experiment:
Apparatus required for the dispersion optics experiment:
Place a glass prism inside the darkroom.
Place the prism in a position where the direct sunlight can fall upon its surface.
Make a small hole in the window shutter of the room so that the sunlight can pass through this hole like a narrow beam.
Fix a white sheet on another side of the wall where the sun says can directly fall on the prism and get the best result via the reflection.
What do you observe after this process? If you look carefully, the light splits into a spectrum of colours. The sunlight (white light) is having colour combinations as violet, indigo, blue, green, yellow, orange, and red.
Scientists have named these combinations of colours VIBGYOR. The letters in the word define each colour that is present in the sunlight.
The result can be observed in the below diagram:
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Result of the Experiment:
When a beam of light is passed through a refracting medium like a glass prism, the light that is least refracted is the red light and highly refracted in Violet.
The sequence of VIBGYOR can be seen in the image below:
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Application of Dispersion
We find the application of dispersion in many other circumstances, such as group velocity dispersion or GVD that causes pulses to scatter in optical fibres, degrading/decreasing the intensity of signals over long distances; also, as a cancellation between group-velocity dispersion and nonlinear effects leads to soliton waves.
FAQs on Dispersion in Physics Explained
1. What is the dispersion of light in Physics?
Dispersion is the phenomenon of the splitting of a beam of white light into its seven constituent colours when it passes through a transparent medium, such as a glass prism. This band of colours is known as a spectrum. The sequence of colours is typically remembered by the acronym VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
2. What is the primary cause of dispersion through a prism?
The primary cause of dispersion is that the refractive index of the prism's material (e.g., glass) is different for different wavelengths of light. According to Cauchy's relation, the speed of light in a medium depends on its colour or wavelength. Since each colour has a unique wavelength, it travels at a slightly different speed inside the prism, causing each colour to refract or bend at a slightly different angle.
3. Why does violet light bend the most and red light the least?
Violet light bends the most because it has the shortest wavelength, which means it travels the slowest inside the prism and experiences the highest refractive index. Conversely, red light has the longest wavelength, travels the fastest, experiences the lowest refractive index, and therefore deviates or bends the least. The angle of deviation is inversely related to the wavelength of the light.
4. What is a common real-world example of dispersion?
The most famous real-world example of dispersion is the formation of a rainbow. In this case, millions of suspended water droplets in the atmosphere act as tiny prisms. When sunlight enters a water droplet, it undergoes refraction and dispersion, splitting into its constituent colours. This is followed by total internal reflection at the back of the droplet before the light refracts again as it exits, forming the vibrant arc of a rainbow in the sky.
5. How is dispersion different from the scattering of light?
While both phenomena involve light interacting with a medium, they are fundamentally different:
Dispersion is the splitting of light into a spectrum of colours because the refractive index of the medium is wavelength-dependent. It happens inside a medium (like a prism or water droplet).
Scattering is the process where light is absorbed and re-emitted in various directions by particles in a medium. It doesn't split colours in the same way, but the intensity of scattering is wavelength-dependent (e.g., blue light scatters more than red light, making the sky appear blue).
6. Can the colours separated by dispersion be recombined?
Yes, the colours can be recombined. Isaac Newton demonstrated this by placing a second, inverted prism in the path of the dispersed spectrum. The second prism collected all the colours and refracted them in the opposite direction, causing them to merge back into a single beam of white light. This experiment proved that the prism itself does not create the colours but merely separates the ones already present in white light.
7. What is chromatic aberration and how does it relate to dispersion?
Chromatic aberration is an undesirable effect in lenses caused by dispersion. Since a lens acts like a series of prisms, it disperses white light, causing different colours to focus at slightly different points. For example, violet light, which bends more, will focus closer to the lens than red light. This results in blurry images with coloured fringes (like purple or green edges) around objects, especially in simple cameras and telescopes.
8. What is the difference between normal and anomalous dispersion?
The key difference lies in how the refractive index of a medium changes with wavelength.
In normal dispersion, the refractive index decreases as the wavelength of light increases. This is the standard behaviour seen in a glass prism, where red light (longer wavelength) bends less than violet light (shorter wavelength).
Anomalous dispersion is a special case that occurs for wavelengths near an absorption band of the medium. In this region, the trend reverses, and the refractive index starts to increase with an increase in wavelength.
