Chapter 2: The human eye and the colourful world Notes

Human Eye

The human eye is the most significant organ of our body and enables us to see various objects and allow us to gather various information about all the objects around us. We see the world around us through our eyes. The light from various objects reaches our eyes and then our eyes transfer the information from the light to the brain and then the brain forms the image of the object around us.

The human eye can be compared to a camera which allows light to pass through its sensor and forms the image. The human eye is a spherical ball of diameter 2.3 cm and is filled with some fluid. The size of eyeballs in all humans is almost fixed but can vary marginally.

Structure of Human Eye

The human eye is a spherical structure of diameter 2.3 cm and there is some fluid filled inside the eye. It is connected to the human skull through some muscles that allow the eyeball to move freely inside the eye cavity. The eye cavity is protected from the outside by the eyelid which provides the required protection to the eyes from foreign particles.

There are various parts of the human eye that are discussed below in the article.

Different Parts of the Eye

The human eye is made up of various parts and all of the parts of the human eye are discussed below.

Human Eye

Vitreous Chamber: The inner volume of the eyeball where the eyeball is placed is called the Vitreous chamber. It maintains the proper pressure within the eye.

Sclera: The outer covering of the eyeball acts as a protective covering and is called the sclera. It is the white part of the eyeball.

Cornea: The part of the eye through which the light enters the eyeball is called the cornea. It is the front part of the Sclera.

Iris: The dark ring-like structure of the eye inside the cornea is called the Iris of the eye. It is the part that provides colour to the eyes and it helps the brain to adjust the exposure of the light entering the eyes.

Pupil: The pupil is a small opening in the Iris that allows the entry of light inside the eyeball. It is controlled by the Iris.

Lens: The lens is actually a lens made of muscles that is placed behind the iris that allows light to converge on the specific point inside the eye to form the image. The lens can adjust its focal length to allow light from all the sources to converge accordingly.

Retina: The light-sensitive layer at the end of the eyeball, where the light ray meets and the image is formed in the retina of the eye and the retina converts this image into electrical impulses that are then sent to the brain.

Optic Nerves: A nerve connected to the retina that transfers all the electrical information to the human brain is called the Optic Nerve. There are two types of optic nerves,

  • Rods: These are the nerve cell that helps in peripheral vision and it is sensitive to even low light.
  • Cones: These are the nerve cell that is used in visualizing various colors and are more sensitive to bright light.

What is Blindspot?

The junction at which the optic nerve meets with the retina has no sensory nerve cell and so if the light ray falls at that spot its image does not forms and thus this spot is called the Blindspot.

Apart from these, there are six different types of muscles that are used for the proper working of the human eye.

Working of the Human Eye

Human eye is a sensory organ that allows us to see by gathering information from the light. It can be compared to the camera and its working is as follows,

  • The light first enters the eye from the cornea.
  • The intensity of the light is then adjusted by the Irisis by changing the size of the pupil.
  • It is then focused in the eye lens, which focuses it to meet at the retina of the eye.
  • Then the image is formed on the retina where rod cells and cone cells capture all the information about the object.
  • The optic nerve then transfers all this information to the brain which then forms the image of the object.

And thus, we see the environment around us.

Function of Human Eye

The eye is a sensory organ that allows light from various objects to fall on its retina and then forms the image of that object. The lens of the eye adjusts automatically to allow the light to properly converge on the retina and then the image formed on the retina is converted to electrical impulses that are transferred to the human brain for further processing through optic nerves.

The amount of light entering the human eye is controlled by the iris and the cornea. The space inside the eyeball is filled with aqueous humor and vitreous humor which allow light to get refracted and meet at the fixed focal point on the retina.

Range of Vision of Human Eye

The human eye is a very incredible instrument that allows us to see at infinite distances till the light from that object can reach our eyes. Thus the far range of the human eye is infinity. We see the stars in the night sky that are very far away from us and the light from them reaches our eyes and thus we see them.

For the near point of the eye, it is the point till which the human eye can see distinctly and the near point of the human eye is, 25 cm, i.e. any object till 25 cm can be distinctly viewed by the human eye.

Lens of Eye

lens placed behind the cornea of the human eye is called the eye lens. It is an optical lens made of proteins and other organic materials. It is situated exactly behind the Iris that allow light to pass through the lens and the eye lens then converges the light to the Retina of the eye.

It is ellipsoidal in shape and is roughly 10 mm long and 4 mm wide. It is made up of translucent protein molecule and thus allow light to pass through it.

What is the work of Lens in Human Eye?

The eye lens of the eye works similarly to other optical lenses that allow light to converge or diverge at a particular point. Similarly, in the eye lens in the human eye, all light converges on the retina of the eye and then the image of the object is formed. The lens in the human eye can adjust its focal length by changing its shape and thus allow the light from any source to focus on the retina of the eye. We can compare the eye lens to any convex lens that can change its focal accordingly.

Defects in Eyes

There are various defects that develop in our eyes because of aging or carelessness. Some of them are mentioned below:

  • Myopia
  • Hypermetropia
  • Presbyopia
  • Cataract
  • Glaucoma
  • Astigmatism

Let’s study their causes and correction in detail.


Cause: Due to a strong refractive index of the eye or elongation of the eyeball

Correction: Shortsightedness is corrected by employing a biconcave (curved inwards) lens that is placed ahead of a myopic eye, moving the image back to the tissue layer and creating it clearer. Hyperopia is corrected by employing a convex (outward-facing) lens.

Hypermetropia (Hyperopia)

Cause: Due to a weak refractive index of the eye or contraction of the eyeball

Correction: Hyperopia will simply be corrected by sporting glasses with connection lenses or contact lenses. Notwithstanding that the degree of ametropia is tiny, correction remains recommended to forestall secondary issues like headaches or eye irritation


Cause: Solidification of lens fluid

Correction: To correct this defect, someone is prescribed a central lens that has each style of lens convex and concave.


Cause: Protein structures of the lens clubbed together

Correction: Cataract surgery involves removing the clouded lens and substituting it with a transparent artificial lens. The unreal lens, known as the associate in the nursing lens, is positioned within the same place as your natural lens. It remains a permanent part of your eye.


Cause: Abnormal pressure inside the eye

Correction: Glaucoma is treated by lowering your eye pressure (intraocular pressure). Betting on your state of affairs, your choices could embody prescription eye drops, oral medications, optical device treatment, surgery, or a mix of any of those.


Cause: Non-uniform curvature of the cornea

Correction: Astigmatism correction nowadays relies on the employment of special toric contact lenses. Astigmatism can even be corrected by reshaping the membrane through LASIK (laser in place keratomileusis) or PRK (photorefractive keratectomy). PRK removes tissue from the superficial and inner layers of the membrane. LASIK removes tissue solely from the inner layer of the membrane.

Care of Eyes

As the eye is one of the most important sensory organs and it is the most delicate one. One must take care of eyes regularly and the steps that should be used are,

  • One has to be compelled to prefer an Associate in Nursing for everyday eye check-ups.
  • Wear spectacles if the modality is found weak.
  • Invariably study or watch TV in good lightweight. Excess or low light can end in problems. Low light can cause strain and winds up in a very severe headache.
  • Do not examine the sharp provider of sunshine a bit like the sun directly. Excess lightweight can injure the eyes.
  • If mud enters into the eye one should not rub them and rather wash them right away.
  • Maintain a regular distance while reading or observing TV.
  • Take a diet to form certain that you simply get the right nutrients.

What is Night Blindness?

Night blindness conjointly referred to as visual disorder could be a defect within the vision within which individuals cannot read things properly in dim lightweight or at midnight. It mainly happens because of the lack of vitamin A in our body. Thus, always take foods that area unit made of vitamin A like broccoli, inexperienced vegetables, carrot, milk, eggs, curd, papaya, mango, etc.

How do Visually Impaired individuals Read and Write?

A visually impaired person is a person that can not see clearly. So reading and writing through normal means is very difficult for them. We can treat their eyes and they can get back their vision and can read normally and if it is impossible for them to get back their vision they can use the Braille system designed for Blind people to read and write.

Braille System

Braille system is a system developed by Louis Braille for the visually impaired person to read and write. In this system, we arrange dots on paper such that their impression can be felt by the touch. And various dots are used to represent various symbols in this system.

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FAQs on Human Eye

Q1: What are some Sensory Organs?


Various sense organs of the human body are,

  • Eyes
  • Ears
  • Nose
  • Tongue
  • Skin

Q2: What are the parts of Human Eye?


The human eye consists of various parts and parts of the human eye are:

  • Sclera
  • Cornea
  • Iris
  • Pupil
  • Lens
  • Retina
  • Optic nerves

Q3: Define Blind Spot?


At the junction of the retina and the optic nerve, there are no sensory nerve cells and if the light ray falls on that point no image is formed. This point is called the Blind Spot.

Q4: Define lens.


A transparent optical instrument that allows light to pass through it is called the lens. It is used to converge or diverge the light at a point. The human eye also has a lens.

Q5: What are the types of Optic Nerves?


The optic nerve carries information from the retina to the brain. They are of two types,

  • Cones
  • Rods

Q6: What are some common defects of human eyes?


Some common eye defects are,

  • Cataract
  • Myopia
  • Hypermetropia
  • Astigmatism

Q7: Do Human Eyes Grow with Age?


No, the human eye does not grow after the birth of the child.

Q8: What is the Range of Vision of Human Eye?


The range of the human eye is the range through which we can see various objects clearly.

The range of the human eye is,

  • For far range: Infinity
  • For near range: 25 cm

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. This phenomenon of bending of light is known as refraction of light.

Refraction of Light

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.

What is Dispersion of Light?

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 Light Through a Prism

Dispersion of Light Through a 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 choose 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 recognized 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. 

Visible Light Spectrum

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.


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). The following examples illustrate the case of atmospheric refractions:

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.

FAQs on Dispersion of Light

Q1: What do you mean by dispersion of light?


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.

Q2: Why planets do not twinkle?


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.

Q3: Why the duration of the day becomes approximately 4 minutes shorter if there is no atmosphere on earth?


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.

Q4: In a prism, light splits into its spectrum of colors, but in a glass slab, it does not. Why?


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.

Q5: What is the relevance of light dispersion into its color spectrum?


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.

Q6: What is Prism?


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

Q7: How rainbow is created in the atmosphere?


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.

What is Dispersion of Light?

Dispersion is defined as the spitting of white light into different colors when passed through a prism. 

The white light after passing through the prism splits into seven different colours namely,
  • Violet
  • Indigo
  • Blue
  • Green
  • Yellow
  • Orange
  • Red

Together these colours are written as VIBGYOR.

Learn more about, Dispersion of Light.

Dispersion 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. Now when the light passes through the prism, it gets refracted this refraction of light makes the light split into various colours and this phenomenon is called the dispersion of light through the prism.

Different colours in the light range have different wavelengths. Therefore, the speed at which they bend varies depending on the wavelength, in which the Violet light bends most, and the Red bends the least. As a result, white light coming out from the prism breaks into the spectrum of the light.

Diagram of Dispersion of Light Through Prism

The image below shows the dispersion of light through a prism and the formation of a spectrum by white light.

Diagram of Dispersion of Light Through Prism

Angle of Deviation

The measure of refraction in the path of light after passing through the prism is measured by measuring the angle of deviation. The angle of deviation is defined as the angle made between the incident ray of light entering the prism and the refracted ray emerging out of the prism.

The deviation of the light waves after passing through the prism is inversely proportional to the wavelength of the light as the wavelength of the Violet light is the least and so the violet light get deviates the most, whereas the wavelength of the red light is the most and hence it gets deviates the least.

The image below shows the angle of deviation:

Angle of Deviation

The visible pattern of the spectrum observed by us when the light passes through the prism is because of the change in the wavelength of the various colour lights.

Visible Light Spectrum

The light disperses into a wide range of colours after passing through a glass prism. We can see this by looking at it from a different perspective. The refractive index associative with a material is not fixed it varies with the frequency of the light used.

  • If white light passes a glass prism it gets refracted twice, first when the light strikes the prism the light ray gets deviated from the air to the glass surface and its speed decreases whereas when the light ray leaves the glass prism it again gets deviated from the glass to the air surface and its speed is increased.
  • Inside the glass prism, the speed of the light rays remains constant.
  • The surface of the prism is not parallel and hence the light ray does not follow the same path and gets deviated.
Visible Light Spectrum

This deviation in the white lights makes the spectrum of the light visible and we observe the visible spectrum of the light. For example, the spectrum observed on the oil drop is the visible spectrum of the light.

Prism Experiment

The first experiment of light passing through the prism was first conducted by the great scientist Newton. He allows white light to pass through a prism hoping to get white light to the other end. But to his surprise, he found that white light gets changed to the spectrum of the seven colours. He named this phenomenon as dispersion of light.

Through this experiment, he concluded that light is made up of a spectrum of light. To further prove his experiment he from some other tests as

  • He allows the light of only one wavelength to pass through the prism and observes the light ray coming out of the prism and found that this ray only gets refracted and so no sign of dispersion.
  • He realized that only white light shows dispersion, as it is made of several colours of light and all these colours of light, have different wavelengths thus their refraction is not the same they all get deviate differently passing through the prism and allowing to form the spectrum of light. 
  • He concludes that violet light has the shortest wavelength and hence it deviates most whereas red light has the highest wavelength and hence it deviates the least.

Examples of Dispersion of Light

Various examples where the dispersion of light is observed are,

Formation of Rainbow 

Dispersion of light is the reason behind the formation of the rainbow. When it rains the tiny water droplets remain in the air. When the sunlight passes through water droplets the light gets dispersed and we see the dispersed light in the form of a Rainbow.

Spectrum observed on Oil Droplets in Water

When oil droplets fall on water, we see the different colours in them. This is because the light undergoes refraction when it passes from the oil to the water medium or vice versa. Hence the light is dispersed and we see the spectrum of different colours in the oil droplets.

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FAQs on Dispersion of Light

Q1: What is Dispersion of Light?


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), this process is known as Dispersion.

Q2: What is Prism?


A prism is glass apparatus made of transparent glass. It has three rectangular lateral surfaces and two triangular faces that are inclined at an angle. It dispersed the white light passing through it.

Q3:What is Refraction of Light?


When the light ray changes its medium of propagation its deviates from its path this phenomenon is called the refraction of the light.

Q4: What is the Difference between Reflection and Refraction of Light?


Refraction of light is the change in the direction of light when it changes its propagation of the medium whereas reflection is the change in direction of the light after striking through a solid surface.

Q5: What are Examples of Refraction of Light?


Various examples of the refraction of light are,

  • Twinkling of Stars
  • Formation of Rainbow
  • Red light of the sky during sunrise and sunset

Q6: What is VIBGYOR Full Form?


When the light ray is passed through the glass prism it gets deviated into the spectrum of the light in the order VIBGYOR and the full form of the VIBGYOR is,

  • Violet
  • Indigo
  • Blue
  • Green
  • Yellow
  • Orange
  • Red

Twinkling of a star due to atmospheric refraction.

What is Refraction of Light?

Well, we all familiar with the reflection of light that when the light hits a polished surface then it bounces back and this phenomenon is known as reflection. But sometimes, the light bends when it passes from one medium to another, and this bending of light is known as refraction. Basically, the cause of refraction is due to the difference in optical density of the two mediums.

Refraction of light in a different medium

In the figure, one can easily understand refraction, firstly the light travels in the air (optical rarer medium) and the moment it strikes the glass slab, it bends as it enters into an optically denser medium.

Causes of Refraction

This theory is quite different from what we have studied about light, in that it always travels in a straight direction. So why does the light refract Well, the main cause of refraction is the speed of the light. Basically, light travels at different speeds in different media. Thus, when the light travels from one medium to another medium then at that point it faces a change in speed. Now it is known whenever light moves from one medium to another then its speed gets alter which causes refraction. Let’s discuss what happens when light enters from air to the glass slab, and then it comes out from the glass slab.

  • When the light ray travels from air to glass slab, then it bends toward normal as the speed gets reduced in the optically denser medium.
  • When the light ray travels from the glass slab to air, then it bends away from the normal as the speed gets increased in the optically rarer medium.

This can be understood that why the speed of light is different in a different medium, by understanding a simple analogy. Suppose you have two pools, one, which is full of water and the other one, which is full of honey. So, tell me in which pool you can swim easily? Of course water, it is less dense than the honey pool.  Now apply the same analogy to light, so when it travels in a rarer medium then it travels with more speed than in a denser medium.

Laws of Refraction

When a beam of light travels from two medium then it follows two laws of refraction:

  1. The first law of refraction states that the incident ray refracted ray and the normal to the interference of the medium lies on the same plane.
  2. The ratio between the sine of the angle of incidence and sine of the angle of refraction is constant to the interference of the medium, also called Snell’s law of refraction.

K = sin i / sin r

where k is constant, i is the angle of incident and r is the angle of refraction. 

Atmospheric Refraction

In this section, we try to understand why does the stars twinkle in the night? Are we seeing stars at correct positions?  And let me tell you one more interesting fact, we see the sun 2 min before sunrise. This is quite interesting but why? So we are going to answer these questions in this section.  As we all now aware of the term refraction and the cause of refraction. So let’s understand atmosphere refraction.

Since we know the change in medium causes refraction likewise our earth is covered with the atmosphere having different layers, and these layers possess different temperatures at different heights, some atmospheric layers are warm and some are cold.  Now the warmer layer of the atmosphere behaves like an optically rarer medium whereas the cooler layer behaves like an optically denser medium. So now we again have different media thus when light passes through different layers of the atmosphere it gets refracted.

In short, the refraction cause due to the earth’s atmosphere is called atmospheric refraction.

Examples of Atmospheric Refraction

Now let’s discuss some examples of atmospheric refraction:

  1. Twinkling of stars: As we discussed earlier the temperature of the atmosphere’s layer is different at a different height which creates different media for refraction. Also, the air is not constant which led to a change in temperature and causes refraction. So, when the atmosphere refracts more light to us the star seems bright. However, when the atmosphere refracts less light than the star seems dim, and this process happens so fast that it seems to us twinkling.
  2. Advanced sunrise and Delay in the sunset: Have you ever wondered that the actual sunset happens much earlier than what you usually see? Yes, you heard it right. When we see sunsets, the light ray coming from the sun goes under refraction and bends towards us. At that time, the sun already crossed the horizon. The sun, we see, is an image that is formed due to refraction that is actually higher than its actual position. This results in the delay of sunset and the same thing happen during sunrise which makes it earlier than the actual one.
  3. The apparent position of the stars: As we discussed in the twinkling of a star that our atmosphere has different layers which cause light to refract, so our atmosphere bends the starlight towards normal,  which causes the apparent position of the star to appear to be slightly different from its actual position.
  4. The Rainbow: In our childhood, we all love to see a rainbow after the rain. The formation of a rainbow involves Reflection, Refraction, and Dispersion. Firstly, the sunlight enters into the water droplet during which it undergoes refraction as well as dispersion. But here we are only concerned about refraction. So, the light bends inside the droplet (due to change in medium) and performs total internal reflection (will discuss in another article) and then comes out where the light again refracts which results in the formation of a rainbow.

Sample Problems

Problem 1: Explain why stars seem higher than their actual position?


Due to Atmospheric refraction, our atmosphere has different air layers having different temperatures at different heights. Thus, this difference of temperature in a different layer of the atmosphere becomes the rarer and denser medium and causes Atmospheric refraction. Hence, the atmosphere bends the starlight towards normal, which causes the apparent position of the star to appear higher than its actual position.

Problem 2: Why only stars twinkle in the night but not the planet?


Since the star appears very small as it is very far from the earth and seems a point source so a continuous change in atmosphere refracts the light causes the twinkling effect. However, the planet which is not so far from our earth appears as collections of a point source, so when light causes dimming the effect produced by the point source on one side of the planet would get canceled out by the brighter effect produced by the point source of light in other parts.

Problem 3: By how much atmosphere refraction causes a delay in the sunset and early sunrise?


The sun appears 2 minutes before the actual sunrise and sunset 2 minutes later than the actual sunset.

Problem 4: Explain why the object seems moving if we look at the object through the hot air over the fire?


This is because of the refraction of light, as the hot air above the fire behave as rarer medium and the colder air further above the hot air behaves as an optically denser medium,  hence refraction takes place and the object seems shaky or moving. 

Problem 5: Write at least three applications of atmospheric refraction?


Following are the application of atmospheric refraction:

  1. Advance sunrise and delay sunset
  2. The apparent position of stars
  3. Formation of rainbow

Problem 6: We know that when light moves from one medium to another causes refraction. Now our atmosphere covers with air only so how does light refract in one medium? Explain in brief.


Well the atmosphere’s layer is not the same, as at different height it has different temperature due to which some layer become optically rarer medium and some become optically denser and this causes atmospheric refraction.

Scattering of Light Definition

When light passes through one medium, some portion of the light is absorbed by the medium’s particles when it goes to another medium, such as air or a glass of water then some intensity of light is radiated in the direction of the coming light but some part of it defected to different direction based on the wavelength of the constituent light. This phenomenon is known as a scattering of light.
Scattering of Light

In the afternoon, you may observe the bending of multicoloured light due to refraction and total internal reflection. Sunlight contains different colours of light, each with a different wavelength that can be separated as it passes through the atmosphere. Rayleigh’s scattering theory can help explain why the sky appears blue and why the sun appears red during sunrise or sunset. The theory states that shorter wavelengths of light, such as blue light, are scattered more easily by atmospheric particles, while longer wavelengths, like red light, pass through with less scattering.

Factors Affecting Scattering of Light

Shorter wavelengths and higher frequencies scatter more due to the waviness of the line and its interaction with a particle. A line is more likely to collide with a particle if it is wavy. Longer wavelengths, on the other hand, have a lower frequency and are straight, which means they have a smaller likelihood of colliding with a particle. Therefore, the scattering of light depends upon the size of the particle and the wavelength of the light. 

Size of the particles 

The colour or wavelengths of the particle scattered depends upon the size of the particles such as 

  • Tiny particles scatter light of a shorter wavelength.
  • Large particles scatter light of a longer wavelength.

Wavelength of the Ray 

Scattering is inversely proportional to the wavelength.

Scattering ∝ 1/λ

where λ denotes the wavelength of the ray. 

As there is inverse proportionality of the wavelength and scattering this means that the light with a higher wavelength scatters more then than light with fewer wavelengths.

Different forms of Scattering of light

Light dispersion takes place in many forms that are discussed below:

  • Elastic Scattering
  • Inelastic Scattering 

Let’s understand these topics in detail.

Elastic Scattering

When the energy of the incident and scattered beams of light is the same, then the scattering is called elastic scattering.

Inelastic Scattering 

When the energy of the incident beam of light and the dispersed beam of light differs. Inelastic scattering is further classified into four types:

  • Rayleigh Scattering
  • Mie Scattering
  • Tyndall Effect
  • Raman Effect

Rayleigh Scattering

When radiation (light) interacts with molecules and particles in the atmosphere that have a smaller diameter than the wavelength of the incoming radiation, Rayleigh scattering occurs. Longer wavelengths scatter more readily when compared to shorter wavelengths. Small particles, such as NO2 and O2, scatter light with shorter wavelengths (like blue and violet visible light). Red light, which has a longer wavelength, scatters more in the atmosphere than blue light. Incoming sunlight travels a larger distance through the atmosphere at sunrise and dusk. Due to the longer route dispersing the short (blue) wavelengths, we only see the longer (red and orange) wavelengths of light.

Mie Scattering

When the wavelength of electromagnetic radiation is similar to the size of air particles, Mie scattering occurs. Mie scattering affects photons in the near-ultraviolet to mid-infrared regions of the spectrum. Mie scattering occurs largely in the lower atmosphere when the sky is overcast, where bigger particles are more frequent. Mie scattering is mostly caused by pollen, dust, and pollution. For example, Mie Scattering makes the clouds appear white.

Tyndall Effect

A variety of tiny particles make up the Earth’s atmosphere. Smoke, small water droplets, suspended dust particles, and air molecules are examples of these particles. The path of a light beam becomes visible when it collides with such little particles. After being diffusely reflected by these particles, the light reaches us. The Tyndall effect is caused by colloidal particles dispersing light. The phenomenon occurs when a fine beam of sunlight enters a smoke-filled room through a small hole. The particles become visible as a result of light scattering. When sunlight penetrates through a dense forest canopy, the Tyndall effect is noticeable. Light is scattered by little water droplets in the mist. The size of the scattering particles determines the hue of the dispersed light. Very small particles scatter shorter wavelength light, while larger particles scatter longer wavelength light. The dispersed light may appear white if the scattering particles are large enough.

Raman Effect

Raman scattering is the scattering of photons at higher energy levels by stimulating molecules. The incident particle’s kinetic energy is either lost or acquired, with Stokes and anti-Stokes components, because the photons are inelastically scattered.

Applications of Scattering of Light

Blue Color of Sky 

Blue colour has a shorter wavelength compared to red colour. Since we know that, scattering ∝ 1/λ. Hence, the blue colour gets scattered most by tiny minute particles in the atmosphere during the daytime. The atmosphere has the presence of various gases such as Nitrogen (N2) and Oxygen (O2). These gas molecules are very small in size and form a colloidal (Gas-in-Gas solution). Small-sized particles scatter rays of shorter wavelengths and blue colour being of shorter wavelength gets scattered more strongly and gives a blue appearance to the sky. The space appears dark to astronauts, as there is no atmosphere. Without the atmosphere tiny particles aren’t there to scatter light, hence giving a dark appearance.

The image added below shows the blue colour of the sky.

Blue Sky

Red Color of Danger Signals 

The wavelength of red colour is longer when compared to other colours of the spectrum (seven colours are formed due to refraction through a prism). As rays of longer wavelength are least scattered by dust and smoke particles, red colour reaches far away distances and would help danger signals to reach faster and to more distant places. All other colours scatter away during the night, and the red colour reaches our eyes.

Red appearance of Sun during Sunrise and Sunset

During sunrise and sunset, the rays have to travel a longer distance through the layers of the atmosphere because they are very close to the horizon. Therefore, all other colours except the red colour scatter away, and the red colour remain. Most of the red light, which is the least scattered by the particles, enters our eyes. Hence, the sun and the sky appear red. At noon, the sun appears white as less of the blue light gets scattered.

Red Sky

Sample Questions on Scattering of Light

Question 1: What colour does the clear sky appear to be during the day? Give an explanation.


Blue is the colour of the sky throughout the day. This is because of the size of air molecules and other fine particles in the atmosphere is smaller than the wavelength of visible light. Due to this, these particles scatter light rays of shorter wavelengths at the blue end more efficiently than light rays of longer wavelengths at the red end. That is why the scattered blue light gives us the impression of a blue sky when it enters our eyes.

Question 2: What is meant by the scattering of light? 


Light scattering is the spreading of light in different random directions. Light scatters when it encounters various types of suspended particles along its path .The colour of scattered light is determined by the size of scattering particles in the environment.

  • The larger dust and water droplets in the atmosphere scatter light with longer wavelengths, giving the dispersed light a white appearance.
  • The very small particles in the environment, such as air molecules, scatter the blue light contained in the white sunlight.

Question 3: Why does the sun appear reddish early in the morning?


At daybreak, the sun rises near the earth’s horizon (early in the morning). Light from the sun near the horizon must travel through vast layers of air and a great distance via the earth’s atmosphere before reaching our sight. The particles in the atmosphere scatter most of the blue light rays with shorter wavelengths near the horizon. As a result, we are exposed to red light with longer wavelengths. As a result, the sun takes on a crimson colour.

Question 4: Why red color is used to make a danger signal or sign?


When red collides with small fog and smoke particles, it scatters the most since it has the longest wavelength (visible spectrum). As a result, we can see the red colour clearly even from a great distance

Question 5: On a foggy day, why does the driver use orange lights instead of white lights?


When a driver uses white light while driving in fog, the tiny droplets of water scatter a lot of blue light. This diffused blue light reduces visibility and makes driving a challenge. Orange light does not scatter due to its larger wavelength, allowing the motorist to see clearly.

FAQs on Scattering of Light

Q1: What is Scattering of Light?


When light travels from one medium to another medium some of it is absorbed by the medium and then some part of the absorbed energy is deflected by particles in different directions due to he different wavelengths of the constituent of the light. This process of deflection of light is called scattering of the light.

Q2: What Causes the Scattering of Light?


The scattering of light is caused by the interaction of the particles and irregularities of the medium from which light passes through and the size of the particles defines the extent of scattering in the medium.

Q3: What are the Different Types of Scattering of Light?


There are various type of the different scattering of light happens, some of which are as follows:

  • Elastic Scattering
  • Inelastic Scattering
    • Rayleigh Scattering
    • Mie Scattering
    • Tyndall Effect
    • Raman Effect

Q4: How does Scattering Affect the Colour of the Sky?


The blue color of the sky is due to the atmosphere present on the earth as particles of the atmosphere absorb the longer wavelengths such as red and scatter the longer wavelengths such as blue. Thus, blue color enters the eye of the humans causing the color of the sky to be blue.

Q5: How does Scattering Affect Visibility?


As some intensity of the light is scattered in the various direction of the atmosphere and the light entering our eyes have less intensity thus, affects the visibility of far away things.

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