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What is Dispersion of Light?

  • Last Updated : 05 Aug, 2021

Aren’t rainbows beautiful? Have you ever wondered how a rainbow comes to be? It is a basic physics phenomenon known as light dispersion. So, what exactly is light dispersion? When white light is transmitted through a prism, it is split into seven component colors. A prism is a transparent optical device with flat, polished surfaces that refract light. Refraction of light refers to the change in the direction of propagation of light as it passes through a different medium.

What is Refraction of Light?

When a light goes from one medium to another, the speed at which it propagates changes, and it bends or refracts as a result. Light is now refracted towards the triangle’s base when it passes through a prism, this results in the refraction of light.

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The wavelengths of different colors in the spectrum of light are varied. As a result, the rate at which they bend varies depending on the wavelength, with violet bending the most due to its shortest wavelength and red bending the least due to its longest wavelength. When white light is refracted via a prism, it disperses into its spectrum of colors as a result of this.



In other words, when white light is transmitted through a prism, it is split into seven component colors. A prism is a transparent optical device with flat, polished surfaces that refract light. Refraction of light refers to the change in the direction of propagation of light as it passes through a different medium.

Dispersion

When light passes through a prism, it is separated into distinct color components. This is referred to as light dispersion. A prism is a transparent glass with two flat surfaces that are angled at an angle. A white light beam is divided into seven hues by a prism: violet, indigo blue, green, yellow orange, and red. The band of colors scattered by light entering a glass prism is referred to as the spectrum.

When white light passes through a glass prism, it separates into its spectrum of seven colors (in order violet, indigo, blue, green, yellow, orange, and red), a process known as Dispersion.

Causes of Dispersion 

  • Because each colors’ light has distinct wavelengths, white light disperses into seven colors. Red light has the longest wavelength in this range of seven colors, while violet light has the shortest.
  • In a vacuum, all colors of light travel at the same speed. However, in any transparent material, such as glass or water, various colors of light move at different rates.
  • Various colors’ lights bend through different angles due to differences in their velocity. Red light travels the fastest through any transparent medium, whereas violet light travels the slowest.
  • As a result, red light bends the least while violet light bends the most.
  • Thus, the dispersion of white light into seven colors happens when various colored photons bend at different angles while passing through a glass prism.

Dispersion of white light by a Prism

Dispersion of white light by a glass prism

When white light passes through a glass prism, it splits into its seven constituent colors, which is known as dispersion of white light. Violet, Indigo, Blue, Green, Yellow, Orange, and Red are among the colors visible. The color sequence is remembered as VIBGYOR. The spectrum is a grouping of seven colors. With respect to the incidence angle, each component color of light bends at a different angle. Violet light bends the least, whereas red light bends the most.

  • White light is made up of seven different colors, including violet, indigo, blue, green, yellow, orange, and red.
  • Monochromatic light is defined as light that has only one color or wavelength, for example, sodium light.
  • Polychromatic light is defined as light that has more than two colors or wavelengths, such as white light.

Prism Experiment

Newton was the first to experiment with light flowing through a prism. He allowed sunlight to pass through the prism, expecting to see white light on the other side of the screen, but instead saw the spectrum of light after dispersion. He had a little intuition about the relevance of this, but he chose to do something else to prove it. 

By adjusting the size of the intake, he was able to enable just one color (and hence only one wavelength of light) to flow through the prism. Obviously, the light ray was refracted and did not disperse farther.

As a result, he recognised that various colors of the light spectrum bend differently because they have distinct wavelengths. He discovered that violet bent the most and red bent the least due to their shorter and longer wavelengths, respectively.

Visible Light Spectrum

In fact, light disperses into its color spectrum in a glass slab as well. We can notice this if we look at it in a specific manner. Before we begin, you should be familiar with refractive indices. They are not consistent. They differ according to the frequency of light and hence the wavelength. White light is refracted twice as it passes through a glass slab or a glass prism. It goes from air to glass and then back to air. It slows down at the first occurrence of refraction and accelerates up at the second? 



So, what occurs in a slab of glass? Because both surfaces are parallel, all light rays slow down and accelerate at the same pace. As a result, it seems to an onlooker that white light has entered and exited the slab. In a prism, however, the situation is different. Because the surfaces are not parallel to each other, the light rays emanating from the prism eventually travel a route that is distinct from one other, resulting in a scattered effect.

Rainbow

A rainbow is an example of white light dispersion. A high number of tiny droplets of water remain hanging in the air shortly after the rain. Each drop functions as a tiny prism. When sunlight strikes these droplets, the white light divides into seven distinct colors. A continuous band of seven colors is formed by the scattered light from a huge number of droplets. Rainbow is the name given to this colored band.

As a result of the dispersion of white light by tiny droplets hanging in the air after the shower, a rainbow is formed.

When the sun is behind the viewer, the rainbow appears.

Atmospheric Refraction

Atmospheric Refraction is the refraction of light induced by the Earth’s atmosphere (which consists of air layers with differing optical densities).

  • Position of Star: The temperature and density of the atmosphere’s many layers are constantly changing. As a result, we have a variety of media. A distant star serves as a light source. When starlight enters the Earth’s atmosphere, it experiences constant refraction as the refractive index changes from rarer to denser. It slants in the direction of normalcy. As a result, the star’s apparent position differs from its true position.
  • Twinkling of Star: Atmospheric refraction is partly to blame. The light from a distant star is concentrated at a single point. Because the physical condition of the Earth’s atmosphere is not stationary, the apparent position of the star changes when the beam of starlight deviates from its course. As a result, the amount of light entering our eyes varies, being bright at times and faint at others. This is referred to as the Star Twinkling Effect.

Sample Problems

Problem 1: What is Dispersion of Light?

Solution:

When white light passes through a glass prism, it separates into its spectrum of colors (in order violet, indigo, blue, green, yellow, orange, and red), a process known as dispersion.

Problem 2: Why planets do not twinkle?

Solution:



Planets are closer to Earth and are perceived as an extended source of light or a collection of many little point sources of light. As a result, the glittering effect will be nullified by the overall amount of light entering our eyes from all individual point sources.

Problem 3: Why the duration of the day becomes approximately 4 minutes shorter if there is no atmosphere on earth?

Solution:

In the morning, when the sun is below the horizon, the sun rises. Because of refraction, the beams of light from the sun below the horizon reach our eyes. Similarly, a few minutes after the sun has set, the sun can be seen. As a result, the length of the day will be extended by 4 minutes. This is due to refraction in the atmosphere. As a result, the sun rises about two minutes earlier than usual and sets about two  minutes later than usual. Atmospheric refraction is responsible for the apparent flattery of the Sun’s disc at sunset and daybreak.

Problem 4: In a prism, light splits into its spectrum of colors, but in a glass slab, it does not. Why?

Solution:

Light, in fact, disperse into its range of colors on a glass slab. If we look at it in a certain manner, we can see it. White light is refracted not once, but twice when it passes through a glass slab or a glass prism. It slows down in the first occurrence of refraction and accelerates up in the second. When the glass is broken, both surfaces are parallel, all light rays slow down and speed up at the same pace. 

As a result, it appears to an onlooker that white light has entered and exited the slab. In a prism, however, the situation is different. Because the surfaces aren’t parallel, the light beams that emerge from the prism eventually take a path that isn’t parallel to each other, resulting in a dispersed effect.

Problem 5: What is the relevance of light dispersion into its color spectrum?

Solution:



Newton discovered that when dispersed light passes through an inverted prism, it recombines to produce white light after passing through the prism. He was the first to use a glass prism to capture the spectrum of sunlight. He tried using a different prism to split the spectrum of white light even more, but he couldn’t generate any more colors. 

He repeated the experiment, this time with the second prism reversed in relation to the first prism. It allowed all the spectrum’s colors to pass through the second prism. On the other side of the second prism, he discovered white light. He came to the conclusion that the Sun is made up of seven different colors that may be seen.

Problem 6: What is Prism?

Solution:

A prism is a triangular object made of glass having two triangular bases and three rectangular sides that are inclined at an angle.

Problem 7: How rainbow is created in the atmosphere?

Solution:

Small prisms are formed by the water droplets. They refract and disperse incident sunlight, then internally reflect it, and ultimately refract it as it exits the raindrop. Because of light dispersion and interference, different colors reach the observer’s eye due to light dispersion and internal reflection. The color red appears at the top of the rainbow and violet appears at the bottom. A rainbow always forms in the opposite direction of the Sun.




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