CBSE Class 10 Science Chapter 10 PDF Notes – The Human Eye and the Colourful World 2026-27

These Class 10 Science Chapter 10 PDF Notes explain The Human Eye and the Colourful World: how the eye works, accommodation, defects of vision and their correction, refraction through a prism, dispersion and the rainbow, atmospheric refraction, and scattering of light.

Board papers commonly ask about myopia and hypermetropia with ray diagrams, the twinkling of stars, the blue colour of the sky and the formation of a rainbow.

Use the table of contents below to jump to the part you need, or read top to bottom for a complete revision of the chapter.

Table of Contents

• Chapter Overview
• Important Topics and Concepts
• Myopia vs Hypermetropia
• Important Definitions and Terms
• Short Answer Questions
• Long Answer Questions
• MCQs with Answers
• Quick Revision Points
• Chapter Summary
• Exam Tips and PYQ Pattern
• Frequently Asked Questions
• Conclusion

Want notes for every chapter? Explore the full Class 10 Science notes on Nextoper, arranged unit-wise and chapter-wise.

Save Free Notes PDF — No Signup Needed! Click Here to Save

Chapter Overview

The human eye works like a camera: light enters through the cornea, is focused by the eye lens and forms a real, inverted image on the retina, which the brain interprets.

The chapter explains how the eye adjusts focus, why some people need spectacles, and how the same ideas of refraction explain beautiful natural effects such as the spectrum of white light, rainbows, twinkling stars, early sunrise and the colours of the sky.

Important Topics and Concepts

Structure of the human eye

• Cornea: thin transparent front membrane; most refraction of light happens here.
• Iris: dark muscular diaphragm that controls the size of the pupil.
• Pupil: opening that regulates how much light enters.
• Eye lens: transparent, flexible lens that adjusts its focal length to focus images.
• Ciliary muscles: change the curvature of the lens.
• Retina: light-sensitive screen with cells that generate signals; the optic nerve carries them to the brain.

Power of accommodation

The ability of the eye lens to change its focal length to see near and far objects clearly. For distant objects, ciliary muscles relax and the lens becomes thin; for near objects, they contract and the lens becomes thick. The near point of a normal eye is about 25 cm (least distance of distinct vision) and the far point is infinity.

Cataract

In old age, the eye lens can become milky and cloudy, causing partial or complete loss of vision. It is treated by cataract surgery.

Defects of vision and correction

• Myopia (near-sightedness): can see near objects clearly but not distant ones. The image forms in front of the retina due to excessive curvature of the lens or elongation of the eyeball. Corrected with a concave lens.
• Hypermetropia (far-sightedness): can see distant objects clearly but not near ones. The near point moves farther than 25 cm and the image forms behind the retina, due to a lens with too long a focal length or a small eyeball. Corrected with a convex lens.
• Presbyopia: with age, the power of accommodation decreases because ciliary muscles weaken and the lens becomes less flexible. Often corrected with bifocal lenses (upper concave, lower convex).

Refraction through a glass prism

A prism has two inclined refracting surfaces. Light bends twice, and the emergent ray is deviated from the original direction. The angle between the incident and emergent rays is the angle of deviation.

Dispersion of white light

When white light passes through a prism, it splits into seven colours (VIBGYOR), forming a spectrum. Each colour bends by a different amount: red bends the least and violet the most. Newton showed that a second, inverted prism recombines the colours into white light.

Rainbow

A rainbow is a natural spectrum seen in the sky opposite the Sun after rain. Tiny water droplets act like small prisms: sunlight is refracted and dispersed on entering a droplet, reflected inside it, and refracted again on leaving.

Atmospheric refraction

• Twinkling of stars: starlight is refracted continuously by air layers of varying density; because stars are point sources, the apparent position and brightness keep changing.
• Planets do not twinkle because they are close and act as extended sources; the variations average out.
• Advance sunrise and delayed sunset: due to refraction, we see the Sun about 2 minutes before it actually rises and 2 minutes after it sets.
• Flickering of objects seen through hot air above a fire also happens due to changing refractive index.

Scattering of light

Tiny particles in the air scatter light. The Tyndall effect is seen when a beam of light passes through smoke, dust or a dense forest canopy. Very fine particles scatter blue light (shorter wavelength) more than red. That is why the sky looks blue. Without an atmosphere, the sky would look dark, as it does to astronauts at very high altitudes. At sunrise and sunset, light travels a longer path through the atmosphere; blue is scattered away and red reaches us, making the Sun look reddish.

Myopia vs Hypermetropia

Important Definitions and Terms

Short Answer Questions

Q1. What is meant by power of accommodation of the eye?

It is the ability of the eye lens to change its focal length using ciliary muscles, so that both near and distant objects can be seen clearly.

Q2. A person with myopia cannot see objects beyond 1.2 m. What type of lens should be used?

A concave lens of suitable power, which diverges light so that the image of distant objects forms on the retina.

Q3. What is the near point and far point of a normal eye?

The near point is about 25 cm and the far point is at infinity.

Q4. Why do stars twinkle but planets do not?

Stars are very far and act as point sources, so changing atmospheric refraction makes their light flicker. Planets are closer and act as extended sources; the changes average out, so they do not twinkle.

Q5. Why does the sky appear blue?

Fine particles in the atmosphere scatter blue light, which has a shorter wavelength, much more than red light. This scattered blue light reaches our eyes from all directions.

Q6. Why does the Sun appear reddish at sunrise and sunset?

Sunlight then travels a longer path through the atmosphere. Most blue light is scattered away, and mostly red light, which is scattered least, reaches our eyes.

Q7. Why does the sky look dark to astronauts in space?

There is almost no atmosphere at very high altitudes, so there is little scattering of light. Without scattering, the sky appears dark.

Q8. What happens to the image distance in the eye when we increase the distance of an object from the eye?

The image distance stays the same, at the retina. The eye changes its focal length (accommodation) to keep the image focused on the retina.

Long Answer Questions

Q1. What is myopia? State its two causes and how it is corrected, with a description of the ray diagram.

Myopia (near-sightedness) is a defect in which a person sees nearby objects clearly but distant objects look blurred. The far point is less than infinity.

Causes: (i) excessive curvature of the eye lens, (ii) elongation of the eyeball.

In a myopic eye, the image of a distant object forms in front of the retina.

Correction: a concave lens of suitable power is used. It diverges the parallel rays so they appear to come from the far point of the eye, and the eye lens then focuses them on the retina.

Diagram tip: Draw (a) the far point of the myopic eye, (b) the image forming in front of the retina, (c) correction with a concave lens forming the image on the retina.

Q2. Explain the formation of a rainbow.

A rainbow appears in the sky after a shower, always on the side opposite the Sun.

Water droplets in the air act like tiny prisms. Sunlight entering a droplet is refracted and dispersed into its colours.

The light is then reflected from the inner back surface of the droplet (internal reflection).

It is refracted again when it leaves the droplet. Because each colour bends differently, the colours separate and reach our eyes at different angles, forming a rainbow with red on the outer side and violet on the inner side.

Q3. What is dispersion of light? Describe Newton’s experiment with two prisms.

Dispersion is the splitting of white light into its seven colours (violet, indigo, blue, green, yellow, orange, red) when it passes through a prism, because each colour bends by a different angle. Red bends least and violet bends most.

Newton passed sunlight through a glass prism and got a spectrum. He then placed a second identical prism upside down in the path of the spectrum.

All the colours recombined and emerged as white light from the second prism. This showed that white light is made of seven colours.

MCQs with Answers

1. The part of the eye that controls the size of the pupil is the
(a) Cornea (b) Iris (c) Retina (d) Lens
Answer: (b) Iris

2. The least distance of distinct vision for a normal eye is
(a) 25 m (b) 2.5 cm (c) 25 cm (d) 2.5 m
Answer: (c) 25 cm

3. Myopia is corrected using a
(a) Convex lens (b) Concave lens (c) Bifocal lens (d) Cylindrical lens
Answer: (b) Concave lens

4. Image in a hypermetropic eye forms
(a) On the retina (b) In front of the retina (c) Behind the retina (d) On the lens
Answer: (c) Behind the retina

5. Which colour bends the most in a prism?
(a) Red (b) Yellow (c) Green (d) Violet
Answer: (d) Violet

6. The danger signal lights are red because red light
(a) Is scattered most (b) Is scattered least (c) Is absorbed by fog (d) Has the shortest wavelength
Answer: (b) Is scattered least – It travels farthest through fog and smoke.

7. Twinkling of stars is due to
(a) Reflection (b) Atmospheric refraction (c) Dispersion (d) Scattering
Answer: (b) Atmospheric refraction

8. Advance sunrise is about
(a) 2 seconds (b) 2 minutes (c) 20 minutes (d) 2 hours
Answer: (b) 2 minutes

9. The light-sensitive screen of the eye is the
(a) Cornea (b) Iris (c) Retina (d) Pupil
Answer: (c) Retina

10. Presbyopia is often corrected using
(a) Concave lens (b) Convex lens (c) Bifocal lens (d) Plane glass
Answer: (c) Bifocal lens

Quick Revision Points

• Cornea does most refraction; iris controls pupil; retina is the screen.
• Ciliary muscles change lens curvature: accommodation.
• Near point 25 cm; far point infinity.
• Myopia → concave lens; hypermetropia → convex lens; presbyopia → bifocal.
• Dispersion: VIBGYOR; red bends least, violet most.
• Rainbow: refraction + dispersion + internal reflection + refraction.
• Twinkling and advance sunrise: atmospheric refraction.
• Blue sky and red sunset: scattering.

Chapter Summary

The human eye forms a real, inverted image on the retina using the cornea and an adjustable lens. Accommodation lets the eye focus on near and far objects. Myopia, hypermetropia and presbyopia are corrected with concave, convex and bifocal lenses, while cataract is treated surgically.

A glass prism deviates light and disperses white light into a spectrum, which also explains the rainbow. Atmospheric refraction makes stars twinkle and gives us advance sunrise and delayed sunset. Scattering of light explains the Tyndall effect, the blue sky and the reddish Sun at sunrise and sunset.

Exam Tips and PYQ Pattern

• Ray diagrams of myopia and hypermetropia (defect and correction) are very common.
• “Give reasons” questions on twinkling, blue sky, red sunset and danger lights appear almost every year.
• Rainbow formation with a labelled droplet diagram is a frequent 3-mark question.
• Remember: VIBGYOR order and that red has the longest wavelength.

Frequently Asked Questions

Why is red used for danger signals?

Red light is scattered least by fog and smoke, so it can be seen from far away.

What is the function of ciliary muscles?

They change the curvature of the eye lens to adjust its focal length.

Why don’t planets twinkle?

Planets are close and appear as extended sources, so the variations in light from different points cancel out.

Conclusion

The Human Eye and the Colourful World links biology with optics. Learn the parts of the eye, the three vision defects with their lenses, and the reasons behind natural phenomena. Practise the diagrams and “give reason” answers, and this chapter becomes quick to score.

More Notes: Class 10 Science Chapter 9: Light – Reflection and Refraction notes | Class 10 Science Chapter 11: Electricity notes | All Class 10 Science notes

Author Bio: Written and reviewed by the Nextoper Editorial Team, a group of CBSE science educators who build chapter notes directly from the NCERT textbook and past board paper patterns.

Freshness Note: These notes follow the NCERT Class 10 Science textbook (Reprint 2026-27) and the CBSE syllabus for the 2026-27 session. Last checked on 7 November 2026.