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By rohit.pandey1
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Updated on 1 Jul 2026, 16:24 IST
The Human Eye and the Colourful World Class 10 CBSE Notes explain how the human eye forms images, how we see colours, how defects of vision are corrected, and how natural phenomena such as dispersion, rainbow formation, twinkling of stars, blue sky and scattering of light occur.
This chapter is important for CBSE Class 10 Science Notes because it combines ray optics, biological structure of the eye, defects of vision, prism-based dispersion, atmospheric refraction and scattering of light.
The Human Eye and the Colourful World Class 10 is an important CBSE Science chapter that explains how the human eye works and how light creates different natural phenomena around us. This chapter is divided into two major parts: the structure and working of the human eye, and the colourful effects of light such as dispersion, scattering and atmospheric refraction.
In the first part, students learn about the human eye as a natural optical instrument. The chapter explains the functions of the cornea, iris, pupil, eye lens, ciliary muscles, retina, rods, cones and optic nerve. It also covers important concepts such as power of accommodation, near point, far point, least distance of distinct vision and persistence of vision. These topics help students understand how the eye focuses on nearby and distant objects.
Students can download The Human Eye and the Colourful World Class 10 Notes PDF for quick revision before school exams, pre-boards and board exams. The PDF should include human eye diagrams, defects of vision ray diagrams, formula-based numericals, dispersion through prism, scattering of light, atmospheric refraction, MCQs, assertion-reason questions and case-study practice.
The human eye works like a natural optical instrument. It uses the cornea, eye lens, iris, pupil and retina to focus light and form a real, inverted image on the retina. The brain interprets this image so that we see objects correctly. The colourful world around us is explained by dispersion, atmospheric refraction and scattering of light.
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The human eye is a natural optical instrument that helps us see objects by detecting light. It forms an image on the retina, and the optic nerve carries the signal to the brain. The brain processes this signal and helps us understand the size, shape, colour and position of objects.
The human eye works in a way similar to a camera. The eye lens focuses light on the retina, just as a camera lens focuses light on the sensor or film.
For this section, add a labelled diagram of the human eye with the following parts:
The human eye is nearly spherical in shape and is protected by the skull. Its main parts work together to focus light on the retina.
| Part of Human Eye | Function |
| Cornea | Transparent front surface that allows light to enter and helps in refraction |
| Iris | Coloured muscular part that controls the size of the pupil |
| Pupil | Opening through which light enters the eye |
| Eye lens | Convex lens that focuses light on the retina |
| Ciliary muscles | Change the curvature of the eye lens for focusing |
| Retina | Light-sensitive screen where image is formed |
| Rods | Photoreceptor cells that help in dim light vision |
| Cones | Photoreceptor cells responsible for colour vision |
| Optic nerve | Carries visual signals from retina to brain |
| Aqueous humour | Transparent fluid between cornea and lens |
| Vitreous humour | Gel-like fluid between lens and retina |
The cornea is the transparent, curved front surface of the eye. It allows light to enter the eye and performs most of the initial refraction of light.
The iris is the coloured part of the eye. It controls the size of the pupil by contracting or relaxing.
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The pupil is the small opening in the centre of the iris. It regulates the amount of light entering the eye.
In bright light, the pupil becomes smaller. In dim light, the pupil becomes larger.
The eye lens is a transparent convex lens. It focuses light on the retina. Its focal length changes with the help of ciliary muscles.
Ciliary muscles hold the eye lens and change its curvature. When we look at nearby objects, the lens becomes thicker. When we look at distant objects, the lens becomes thinner.
The retina is the light-sensitive layer at the back of the eye. It acts like a screen where the image is formed.
Rods and cones are light-sensitive cells present in the retina.
| Photoreceptor | Function |
| Rods | Help in vision in dim light |
| Cones | Help in colour vision and bright light vision |
The optic nerve carries electrical signals from the retina to the brain. The brain interprets these signals and forms the final visual experience.
Light rays from an object enter the eye through the cornea and pupil. These rays are refracted by the eye lens and focused on the retina. The image formed on the retina is real, inverted and diminished. The retina converts this image into electrical signals, which are carried by the optic nerve to the brain. The brain interprets the signals so that we see the object upright.
| Feature | Description |
| Lens used | Convex lens |
| Image formed on | Retina |
| Nature of image | Real and inverted |
| Size of image | Diminished |
| Final interpretation | Brain makes us perceive it upright |
Power of accommodation is the ability of the eye lens to adjust its focal length to see nearby and distant objects clearly.
The eye lens changes its curvature with the help of ciliary muscles. When we look at a distant object, the ciliary muscles relax and the lens becomes thin. When we look at a nearby object, the ciliary muscles contract and the lens becomes thick.
| Object Position | Ciliary Muscles | Eye Lens | Focal Length |
| Distant object | Relax | Thin | Increases |
| Nearby object | Contract | Thick | Decreases |
Power of accommodation is the ability of the eye lens to change its focal length so that images of objects at different distances can be focused clearly on the retina.
The near point is the minimum distance at which an object can be seen clearly without strain.
For a normal human eye, the near point is:
25 cm
This distance is also called the least distance of distinct vision.
The far point is the farthest point up to which the eye can see objects clearly.
For a normal human eye, the far point is:
Infinity
For a normal eye, the range of vision is from:
25 cm to infinity
The least distance of distinct vision is the minimum distance at which the eye can see an object clearly without strain. For a normal human eye, it is 25 cm.
This is why books and notebooks are usually held at around 25 cm from the eyes while reading.
Persistence of vision is the ability of the eye to retain an image for about 1/16th of a second after the object is removed.
This principle is used in movies and animation. A sequence of still images shown rapidly appears as continuous motion because the previous image remains in the eye for a very short time.
Defects of vision occur when the eye cannot focus light properly on the retina. These defects may occur due to changes in the shape of the eyeball, changes in the focal length of the eye lens, weakening of ciliary muscles or loss of flexibility of the lens.
The main defects of vision studied in Class 10 are:
Myopia, or short-sightedness, is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects clearly.
In myopia, the image of a distant object is formed in front of the retina instead of on the retina.
Myopia may occur due to:
A person with myopia:
Myopia is corrected using a concave lens of suitable power. A concave lens diverges the incoming light rays before they enter the eye. This helps the eye lens focus the image on the retina.
Add two diagrams:
Myopia is corrected by using a concave lens because it diverges light rays and helps form the image on the retina.
Hypermetropia, or long-sightedness, is a defect of vision in which a person can see distant objects clearly but cannot see nearby objects clearly.
In hypermetropia, the image of a nearby object is formed behind the retina instead of on the retina.
Hypermetropia may occur due to:
A person with hypermetropia:
Hypermetropia is corrected using a convex lens of suitable power. A convex lens converges light rays before they enter the eye, helping the image form on the retina.
Add two diagrams:
Image alt text: correction of hypermetropia ray diagram class 10
Hypermetropia is corrected by using a convex lens because it converges light rays and helps focus the image on the retina.
Presbyopia is an age-related defect of vision in which a person finds it difficult to see nearby objects clearly.
It occurs because the ciliary muscles become weak and the eye lens loses flexibility with age. Due to this, the eye cannot adjust its focal length properly.
Presbyopia is corrected using suitable convex lenses. Some people may suffer from both myopia and hypermetropia with age. In such cases, bifocal lenses may be used.
A bifocal lens has two parts:
| Part of Bifocal Lens | Function |
| Upper part | Concave lens for distant vision |
| Lower part | Convex lens for near vision |
Bifocal lenses are commonly used by people who have both near-vision and distant-vision problems.
Astigmatism is a defect of vision caused by uneven curvature of the cornea or eye lens. A person with astigmatism may not see horizontal and vertical lines equally clearly.
It is corrected using cylindrical lenses of suitable power.
Cataract is a condition in which the eye lens becomes cloudy or opaque, causing blurred vision. It commonly occurs with age. Cataract is different from myopia and hypermetropia because it is not corrected simply by ordinary concave or convex lenses. It is usually treated medically, often through lens replacement surgery by qualified eye specialists.
| Basis | Myopia | Hypermetropia |
| Also called | Short-sightedness | Long-sightedness |
| Nearby objects | Seen clearly | Not seen clearly |
| Distant objects | Not seen clearly | Seen clearly |
| Image forms | In front of retina | Behind retina |
| Cause | Eyeball too long or lens too curved | Eyeball too short or lens has large focal length |
| Corrective lens | Concave lens | Convex lens |
| Lens power | Negative | Positive |
| Defect | Main Problem | Cause | Correction |
| Myopia | Distant objects not clear | Elongated eyeball or high lens curvature | Concave lens |
| Hypermetropia | Nearby objects not clear | Short eyeball or weak converging power | Convex lens |
| Presbyopia | Nearby vision weak with age | Weak ciliary muscles and less flexible lens | Convex or bifocal lens |
Defect-of-vision numericals are usually based on the lens formula and power of lens.
Use:
1/f = 1/v - 1/u
and
P = 1/f
where f is measured in metres for power calculation.
A myopic person cannot see objects clearly beyond 80 cm. Find the power of the lens required to correct this defect.
For a myopic person, the far point is 80 cm. To see distant objects clearly, the corrective lens should form a virtual image of an object at infinity at the person’s far point.
Given:
u = -∞
v = -80 cm = -0.80 m
Using lens formula:
1/f = 1/v - 1/u
Since u = -∞, 1/u = 0
1/f = 1/(-0.80) - 0
1/f = -1.25
f = -0.80 m
Power:
P = 1/f
P = 1/(-0.80)
P = -1.25 D
The person needs a concave lens of power -1.25 D.
A hypermetropic person has a near point of 1 m. Find the power of the lens required so that the person can read at 25 cm.
For normal reading, the object should be at 25 cm. The corrective lens should form a virtual image at the person’s near point, which is 1 m.
Given:
u = -25 cm
v = -100 cm
Using lens formula:
1/f = 1/v - 1/u
1/f = 1/(-100) - 1/(-25)
1/f = -1/100 + 1/25
1/f = -0.01 + 0.04
1/f = 0.03 cm⁻¹
f = 33.3 cm = 0.333 m
Power:
P = 1/f
P = 1/0.333
P = +3 D
The person needs a convex lens of power approximately +3 D.
The “Colourful World” part of the chapter explains how light produces colours and why several natural phenomena occur in the atmosphere.
Important topics include:
A glass prism is a transparent optical object with triangular faces. When a ray of light passes through a prism, it bends twice: first when entering the prism and second when leaving it.
The emergent ray bends away from the original direction of the incident ray. This bending is called deviation.
The angle between the direction of the incident ray and the emergent ray is called the angle of deviation.
A prism diagram should include:
Dispersion of light is the splitting of white light into its seven constituent colours when it passes through a glass prism.
White light consists of seven colours. When it passes through a prism, different colours bend by different amounts due to their different wavelengths. This produces a band of colours called the spectrum.
The seven colours of the spectrum are remembered using the word VIBGYOR.
| Letter | Colour |
| V | Violet |
| I | Indigo |
| B | Blue |
| G | Green |
| Y | Yellow |
| O | Orange |
| R | Red |
Violet deviates the most because it has the shortest wavelength among the visible colours and slows down the most in glass.
Red deviates the least because it has the longest wavelength among the visible colours and slows down the least in glass.
Different colours of light travel at different speeds in glass. Violet light has a shorter wavelength and experiences a higher refractive index in glass, so it bends the most. Red light has a longer wavelength and experiences a lower refractive index, so it bends the least.
When the spectrum produced by one prism is passed through a second identical prism placed in an inverted position, the seven colours recombine to form white light.
This shows that white light is made up of seven colours.
A rainbow is formed due to dispersion, refraction and internal reflection of sunlight by tiny water droplets present in the atmosphere.
A rainbow is formed when sunlight is refracted, dispersed and internally reflected by water droplets in the atmosphere. The droplets act like tiny prisms and split white sunlight into seven colours.
Atmospheric refraction is the bending of light as it passes through layers of the Earth’s atmosphere having different optical densities.
The Earth’s atmosphere is not uniform. Its density changes with height. As light passes through different layers of the atmosphere, it bends continuously.
Atmospheric refraction explains:
Stars twinkle due to atmospheric refraction. Stars are very far away and behave like point sources of light. As starlight passes through different layers of the atmosphere, it bends continuously. The amount of bending keeps changing because the atmosphere is unstable. As a result, the apparent position and brightness of the star keep changing, making it appear to twinkle.
Stars twinkle because their light undergoes continuous atmospheric refraction through layers of air with changing density. Since stars act as point sources of light, small changes in the path of light cause noticeable changes in brightness.
Stars are very far away and appear as point sources of light. Planets are much closer and appear as extended sources of light. The light coming from different points of a planet averages out the fluctuations caused by atmospheric refraction. Therefore, stars twinkle but planets usually do not.
| Basis | Stars | Planets |
| Distance from Earth | Very far | Comparatively closer |
| Source type | Point source | Extended source |
| Effect of atmospheric refraction | Strong visible fluctuation | Fluctuations average out |
| Twinkling | Yes | Usually no |
Due to atmospheric refraction, the Sun appears above the horizon even when it is actually slightly below the horizon. This makes sunrise appear earlier and sunset appear later than the actual time.
We see the Sun before actual sunrise because sunlight bends due to atmospheric refraction. This bending makes the Sun appear above the horizon even when it is still below the horizon.
Scattering of light is the phenomenon in which light rays get redirected in different directions after striking tiny particles present in a medium.
Scattering explains many natural phenomena, such as:
Tyndall effect is the scattering of light by colloidal particles.
When a beam of light passes through a colloidal solution or a medium containing very fine particles, its path becomes visible due to scattering. This is called the Tyndall effect.
| Example | Explanation |
| Sunlight entering a dusty room | Dust particles scatter light |
| Headlight beam in fog | Fog droplets scatter light |
| Light passing through colloidal solution | Colloidal particles scatter light |
| Projector beam in a cinema hall | Dust particles make the path visible |
The sky appears blue because sunlight is scattered by tiny molecules and particles in the atmosphere. Blue light has a shorter wavelength than red light, so it is scattered more strongly. This scattered blue light reaches our eyes from all directions, making the sky appear blue.
The sky appears blue because blue light has a shorter wavelength and is scattered more by air molecules in the atmosphere. This scattered blue light reaches our eyes from different directions.
The sky appears dark to astronauts because space has no atmosphere to scatter sunlight. Since there are no air molecules to scatter blue light, the sky appears black or dark.
Danger signals are red because red light has the longest wavelength among visible colours. It is scattered the least by fog, dust and smoke, so it can travel a longer distance and be seen clearly from far away.
At sunrise and sunset, sunlight travels a longer distance through the atmosphere. Most of the shorter wavelength colours such as blue and violet are scattered away. The longer wavelength red and orange light reaches our eyes, making the Sun appear reddish.
Syllabus note: The current CBSE 2026–27 curriculum mentions scattering of light and applications in daily life, but specifically excludes the colour of the Sun at sunrise and sunset from summative assessment. It can still be useful for conceptual clarity, older NCERT-based material and general understanding.
| Basis | Dispersion | Scattering |
| Meaning | Splitting of white light into seven colours | Redirection of light by small particles |
| Cause | Different colours bend by different amounts | Light interacts with tiny particles |
| Medium | Prism or water droplets | Atmosphere, colloids, fog, dust |
| Example | Rainbow, prism spectrum | Blue sky, Tyndall effect |
| Wavelength role | Different wavelengths refract differently | Shorter wavelengths scatter more |
| Result | Spectrum is formed | Light spreads in different directions |
Students should practise the following diagrams:
| Diagram | Why Important |
| Human eye labelled diagram | Common diagram-based question |
| Myopia and its correction | Important defect of vision diagram |
| Hypermetropia and its correction | Important defect of vision diagram |
| Refraction through prism | Needed for dispersion explanation |
| Dispersion of white light | Explains VIBGYOR spectrum |
| Rainbow formation | Stepwise natural phenomenon |
| Atmospheric refraction | Explains twinkling and sunrise/sunset |
| Tyndall effect | Explains scattering in colloids |
| Concept | Formula / Value |
| Least distance of distinct vision | 25 cm |
| Far point of normal eye | Infinity |
| Persistence of vision | 1/16 second |
| Lens formula | 1/f = 1/v - 1/u |
| Power of lens | P = 1/f |
| Unit of power | Dioptre D |
| Concave lens power | Negative |
| Convex lens power | Positive |
A. Virtual and erect
B. Real and inverted
C. Virtual and enlarged
D. Real and erect
Answer: B. Real and inverted
A. 10 cm
B. 15 cm
C. 25 cm
D. 50 cm
Answer: C. 25 cm
A. Convex lens
B. Concave lens
C. Plane mirror
D. Prism
Answer: B. Concave lens
A. Concave lens
B. Convex lens
C. Cylindrical mirror
D. Glass slab
Answer: B. Convex lens
A. Scattering
B. Dispersion
C. Reflection
D. Absorption
Answer: B. Dispersion
A. Red
B. Yellow
C. Green
D. Violet
Answer: D. Violet
A. Reflection
B. Atmospheric refraction
C. Dispersion
D. Magnetic effect
Answer: B. Atmospheric refraction
A. Dispersion
B. Scattering
C. Total internal reflection
D. Absorption
Answer: B. Scattering
A. Metre
B. Dioptre
C. Newton
D. Joule
Answer: B. Dioptre
A. True solution
B. Colloidal solution
C. Pure water only
D. Vacuum
Answer: B. Colloidal solution
Assertion: Stars appear to twinkle.
Reason: Starlight undergoes atmospheric refraction through layers of air with changing density.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Assertion: Myopia is corrected using a concave lens.
Reason: A concave lens diverges light rays before they enter the eye.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Assertion: The sky appears blue.
Reason: Blue light is scattered more than red light by particles in the atmosphere.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Assertion: Violet light deviates more than red light in a prism.
Reason: Violet light has a shorter wavelength than red light.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Assertion: Planets usually do not twinkle.
Reason: Planets behave as extended sources of light, so brightness fluctuations average out.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
A student sitting in the last row of the classroom is unable to read the writing on the board clearly, but the student can read a book kept nearby without difficulty. The eye doctor explains that the image of distant objects is forming in front of the retina and prescribes a suitable lens.
A student observes that when white light passes through a glass prism, it splits into seven colours. The student also notices that violet colour bends more than red colour.
During a foggy morning, a student notices that the beam of a vehicle’s headlight becomes visible. The teacher explains that tiny water droplets in fog scatter light, making the path of light visible.
| Mistake | Correct Concept |
| Writing myopia is corrected by convex lens | Myopia is corrected by concave lens |
| Writing hypermetropia is corrected by concave lens | Hypermetropia is corrected by convex lens |
| Forgetting sign of concave lens power | Concave lens power is negative |
| Confusing dispersion and scattering | Dispersion splits white light; scattering redirects light |
| Writing planets twinkle like stars | Planets usually do not twinkle |
| Forgetting near point of normal eye | Near point is 25 cm |
| Forgetting persistence of vision value | Image remains for about 1/16 second |
| Writing red deviates most | Violet deviates most; red deviates least |
The Human Eye and the Colourful World is an important Class 10 Science Syllabus because it connects the working of the human eye with real-life optical phenomena. Students should focus on the structure of the human eye, power of accommodation, defects of vision, correction of myopia and hypermetropia, dispersion of light, VIBGYOR, rainbow formation, atmospheric refraction, twinkling of stars, scattering of light and Tyndall effect.
For scoring well, practise labelled diagrams, ray diagrams for vision defects, comparison tables, direct “why” questions, formula-based numericals, MCQs, assertion-reason questions and case-study questions.
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The Human Eye and the Colourful World Class 10 explains the structure and working of the human eye, defects of vision and their corrections, dispersion of light, atmospheric refraction, scattering of light, Tyndall effect and natural optical phenomena.
In many updated Class 10 Science resources, The Human Eye and the Colourful World is referred to as Chapter 10. In older NCERT editions and many existing notes, it appears as Chapter 11. Students should follow the chapter number used in their school textbook.
The retina acts as a light-sensitive screen at the back of the eye. It contains rods and cones and converts the image formed by the eye lens into electrical signals.
Power of accommodation is the ability of the eye lens to adjust its focal length to see nearby and distant objects clearly.
The near point of a normal eye is 25 cm. It is also called the least distance of distinct vision.
The far point of a normal eye is infinity. A normal eye can see very distant objects clearly.
Myopia is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects clearly. It is corrected using a concave lens.
Hypermetropia is a defect of vision in which a person can see distant objects clearly but cannot see nearby objects clearly. It is corrected using a convex lens.
Presbyopia is an age-related defect of vision in which the eye gradually loses its power of accommodation. It is commonly corrected using convex or bifocal lenses.
A rainbow is formed when sunlight undergoes refraction, dispersion and internal reflection inside water droplets present in the atmosphere.
Atmospheric refraction is the bending of light as it passes through layers of the atmosphere with different densities.
Danger signals are red because red light has the longest wavelength and is scattered the least, so it can be seen from a long distance.
Tyndall effect is the scattering of light by colloidal particles. It makes the path of a light beam visible in a colloid, fog or dusty air.
VIBGYOR is the order of colours in the spectrum: Violet, Indigo, Blue, Green, Yellow, Orange and Red.
Planets do not usually twinkle because they are closer to Earth and appear as extended sources of light. The fluctuations from different points average out.
Stars twinkle because their light undergoes continuous atmospheric refraction through layers of air with changing density.