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Dispersion of Light by Prism

  • Last Updated : 20 Jul, 2021

Light dispersion happens when white light is split into its constituent hues due to refraction and Snell’s law. White light looks white simply because it contains every hue in the visible spectrum. Despite their near proximity, the index of refraction for each color is distinct in non-vacuous materials. Because of these distinct indices, each wavelength takes a different route.

Light dispersion is the breaking of white light into its constituent colors as a result of the surface’s refractive index and the wavelength of the light.

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 Dispersion of Light 

Dispersion is defined as the separation of white light into different colors when light is transmitted to a prism. The scattering of light depends on the length of the light. Therefore, it can be argued that the degree of deviation depends on the wavelengths. Deviation from the light path is the opposite of the standard length.



White light is mainly associated with the light of different wavelengths (colors). Violet, indigo, blue, green, yellow, and red with a very long length while violet has a very low length.

The red light has a slight deviation and very violet. As all long distances suffer from a variety of deviations, when white light passes from one to another, different colors of the light split, and this object of light dispersion into its parts as a result of refraction.

Dispersion of Light through a prism

Refraction Of Light Through Prism

When light passes from one medium to another medium speed of propagation of light changes as a result the light is refracted or the light is bent. Now when the light passes through the r prism, refracted towards the base of the triangle.

Different colors in the light range have different wavelengths. Therefore, the speed at which they bend all varies depending on the wavelength, in which the violet bends most, the short distance and the red curve slightly, and has the longest length.

As a result, the scattering of white light in its color range occurs when it is emitted by a prism.

Visible Light Spectrum

The light disperses into a wide range of colors on a glass slide. We can see this by looking at it from a different perspective. Before we move on you should know something about refractive indices. They do not change constantly. They vary in frequency of light which is why their wavelengths.

Now, in order for the white light to pass through the glass slide or glass prism, it is emitted not once, but twice. It starts from the air into the glass and then from the glass to the air. At the first instance of refraction, slow down and the second speed straight?



Now what happens to the glass container is All light rays slow down and accelerate at the same rate because both the surfaces are parallel. And then, to the observer, it would seem that white light had penetrated and left the slide. But this case is different from the prism.

The surfaces aren’t parallel to each other, so the light rays out of the prism finally follow the path that is different from each other, giving a scattered effect.

Prism Experiment

Newton was the first to make this experiment by transmitting light through a prism. He let the sunlight pass through the prism expecting to see the white light on the screen set to one side but instead, he saw the spectrum of light after the scattering. He was a little skeptical about the importance here but decided to do something here to confirm it.

By controlling the intensity of the incoming light, he allowed only one color to pass through the prism. Apparently, the ray of light was refracted and didn’t undergo any further dispersion.

Therefore, he noticed that different colors of the spectrum of light bend differently as they have different wavelengths.  He made the impression that violet bent the most and red the least because of their shorter and longer wavelengths respectively.

Some examples where the dispersion of light take place:

Rainbow: Dispersion of light is the reason behind the rainbow. When it rains the tiny water droplets remain in the air. When the sunlight passes through water droplets the light is dispersed. We will see the dispersed light in the form of a Rainbow.

Oil droplets on water: When an oil droplet falls on water, we will be able to see the different colors in them. This is because the light undergoes refraction when it passes from oil medium to water medium or vice versa. Hence the light is dispersed and we will be able to see different colors

Prism

Prism is a transparent, homogeneous refracting substance (such as glass) surrounded by two inclined plane refracting surfaces at a fixed angle termed the refracting angle of prism angle It features two triangle bases and three rectangular lateral surfaces that are inclined to each other.



The angle of the prism is the angle at which the surfaces are slanted. It’s also referred to as the refracting angle. 

The angle of deviation of a prism is the angle between the incident and emerging rays.

The angle of incidence is the angle formed by the normal and the ray of light when a beam of light strikes a surface at a specific location. 

The angle of emergence refers to the angle at which light emerges or comes out from a prism.

Refraction Of Light Through Prism

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. 

The wavelengths of different colours 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 colours as a result of this.

Dispersion 

When white light passes through a glass prism, it separates into its spectrum of 7 colours (in order violet, indigo, blue, green, yellow, orange, and red), a process known as dispersion.



Dispersion of white light by a glass prism: When white light passes through a glass prism, it splits into its seven constituent colours, which is known as dispersion of white light. Violet, Indigo, Blue, Green, Yellow, Orange, and Red are among the colours visible. The colour sequence is remembered as VIBGYOR. The spectrum is a grouping of seven colours. With respect to the incidence angle, each component colour 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 colours, including violet, indigo, blue, green, yellow, orange, and red.

Monochromatic light is defined as light that has only one colour or wavelength, for example, sodium light.

Polychromatic light is defined as light that has more than two colours or wavelengths, such as white light.

Prism Experiment

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 colours. He repeated the experiment, this time with the second prism reversed in relation to the first prism. It allowed all of the spectrum’s colours 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 colours that may be seen.

Visible Light Spectrum

Light, in fact, disperse into its range of colours 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.



Rainbow: The spectrum of sunshine in nature is known as a rainbow. It is generated when sunlight is dispersed by a tiny water droplet present in the atmosphere

The rainbow’s creation: 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 colours reach the observer’s eye due to light dispersion and internal reflection. The colour 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.

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 into 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 colours (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 become approximately 4 min 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 2 minutes earlier than usual and sets about 2 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: 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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