Home

CBSE Class 10 Science Notes Chapter 11 Human Eye and Colourf...

CBSE Class 10 Science Notes Chapter 11 Human Eye and Colourful World

Author at PW

February 06, 2026

Human eye class 10 notes explain how our eyes work as natural optical instruments to see the world. This chapter covers the eye's anatomy, common vision defects like myopia, and beautiful natural phenomena like rainbows. You’ll also learn how light refracts through prisms and scatters in the atmosphere to make the sky look blue.

Check out: CBSE Class 10th Books

Class 10 Science Human Eye and Colourful World Notes

The human eye is a crucial sensory organ. It enables us to see and understand the vibrant world.

Structure of the Human Eye

The human eye is nearly spherical with a diameter of about 2.3 cm. It consists of several key parts:

Cornea: This is the thin, transparent, bulging front part. It refracts most of the incoming light. The cornea also protects the eye from dust and germs.
Iris: A dark, muscular diaphragm behind the cornea. It controls the size of the pupil.
Pupil: A small opening in the centre of the iris. It regulates the amount of light entering the eye.
Crystalline Lens: This is a transparent, flexible, convex lens. It forms real and inverted images on the retina.
Ciliary Muscles: These muscles adjust the focal length of the eye lens. They help in focusing on objects at different distances.
Retina: A light-sensitive screen at the back of the eye. It contains rods and cones. Rods help in dim light vision, while cones detect colour and bright light.
Optic Nerve: This nerve transmits electrical signals from the retina to the brain. The brain then interprets these signals into images.
Aqueous Humour: A water-like fluid found between the cornea and the lens. It provides nutrition to the eye.
Vitreous Humour: A gel-like substance located between the lens and the retina. It helps maintain the eye's shape.

Working of the Human Eye

Light enters the eye through the cornea and pupil. The crystalline lens focuses this light onto the retina. The retina converts light into electrical signals. The optic nerve carries these signals to the brain. The brain then processes these signals, allowing us to see objects.

Power of Accommodation

This is the eye lens's ability to adjust its focal length. For near objects, ciliary muscles contract, making the lens thicker and decreasing focal length. For distant objects, muscles relax, making the lens thinner and increasing focal length. This ensures images always focus sharply on the retina.

Near Point and Far Point

The near point is the minimum distance for clear vision. For a normal young adult, it is 25 cm. The far point is the maximum distance for clear vision. For a normal eye, the far point is at infinity.

Defects of Vision and Correction

Several common eye defects can affect vision.

Myopia (Nearsightedness): A person sees nearby objects clearly but distant objects blur. This happens when the image forms in front of the retina. Causes include excessive lens curvature or an elongated eyeball. It is corrected using a concave lens.

Hypermetropia (Farsightedness): A person sees distant objects clearly but nearby objects blur. The image forms behind the retina. Causes include too long focal length of the lens or a shortened eyeball. It is corrected using a convex lens.

Presbyopia: This age-related defect makes it difficult to see nearby objects. It results from weakening ciliary muscles and reduced flexibility of the eye lens. Bifocal lenses often correct this condition.

Cataract: The crystalline lens becomes cloudy or opaque, causing partial or complete vision loss. It is treated with surgery to replace the clouded lens.

Dispersion of Light by a Prism

Dispersion is the splitting of white light into its component colours. A glass prism causes this phenomenon. Different colours of light bend at different angles when passing through a prism. Violet light bends the most, while red light bends the least. This creates a spectrum of colours, like a rainbow.

Atmospheric Refraction

Atmospheric Refraction is the bending of light as it travels through different layers of the Earth’s atmosphere. Since the atmosphere is made up of layers with varying temperature and density, the refractive index changes continuously from higher layers to lower layers. As a result, light rays do not travel in a straight line but bend gradually towards the Earth.

Twinkling of Stars:
Stars appear to twinkle because the light coming from them undergoes continuous atmospheric refraction due to constantly changing air currents. These changes cause fluctuations in the apparent position and brightness of stars. Since stars are very far away and act as point sources of light, even small changes in refraction make them appear to twinkle.

Advance Sunrise and Delayed Sunset:
Atmospheric refraction causes the Sun to appear above the horizon even when it is actually below it. Due to this effect, we can see the Sun about 2 minutes before actual sunrise and about 2 minutes after actual sunset. This happens because sunlight bends while passing through the dense layers of the atmosphere near the Earth’s surface.

Scattering of Light

Scattering of Light is the phenomenon in which light rays deviate from their straight path when they strike small particles present in a medium such as air, dust, smoke, or water droplets. This occurs because light interacts with these particles and gets redirected in different directions.

Tyndall Effect:
The Tyndall effect refers to the scattering of light by colloidal particles, making the path of a light beam visible. This effect is commonly observed when a beam of sunlight passes through a dusty or smoky room, or when light passes through fog or mist. It helps distinguish between true solutions and colloids.

Blue Colour of the Sky:
The sky appears blue because air molecules scatter light of shorter wavelengths, such as blue and violet, much more effectively than red light. Although violet light scatters the most, our eyes are more sensitive to blue light, and some violet light is absorbed by the upper atmosphere. As a result, the scattered blue light reaches our eyes from all directions, making the sky appear blue.
Reddening of the Sun at Sunrise and Sunset:
At sunrise and sunset, sunlight travels a longer distance through the atmosphere to reach the observer. During this long path, most of the blue and shorter wavelength light is scattered away, leaving mainly the red and orange wavelengths to reach our eyes. This causes the Sun to appear reddish at these times.
Danger Signals: These are red because red light is least scattered by fog or smoke, making it visible from a distance.

Check out: CBSE Class 10th Sample Papers

Anatomy of the Human Visual System

The eye is a natural optical device that allows us to perceive our surroundings. It is almost spherical, with an average diameter of 2.3 cm. It functions like a camera, focusing light to create a real, inverted image on a sensitive screen called the retina.

Critical Components for Vision

Cornea: A thin, transparent membrane where most light refraction happens.
Iris & Pupil: The iris is a muscular ring that changes the pupil's size to control light.
Crystalline Lens: A flexible convex lens that provides the fine-tuning for focus.
Ciliary Muscles: These muscles contract or relax to change the shape of the lens.
Retina: The back screen of the eye filled with light-sensitive cells called rods and cones.
Optic Nerve: It converts the image into electrical signals and sends them to the brain.

Understanding Eye Focus Power

The ability of your eye to see objects at different distances is called "Accommodation."

Near Point: The closest distance you can see clearly without strain (25 cm).
Far Point: The maximum distance for clear vision (Infinity for a normal eye).
Adjustment: For far objects, ciliary muscles relax (thin lens). For near objects, they contract (thick lens).

Check Out: CBSE Class 10 Question Banks

Solving Common Vision Related Issues

When the eye cannot focus light directly on the retina, vision becomes blurry. These refractive errors are very common but easily manageable. Students often use human eye class 10 notes pdf download and resources from human eye class 10 notes prashant kirad to master these ray diagrams for exams.

Breakdown of Eye Defects

Myopia: You can see near things but not far ones. It's caused by a long eyeball or a lens that is too curved.
Hypermetropia: You can see far things but not near ones. This happens if the eyeball is too short.
Presbyopia: As we get older, the lens loses flexibility, making it hard to see things up close.
Cataract: A cloudy membrane grows over the lens, blocking light. This requires surgery.

Correction Guide Table

Condition	Image Focus Point	Corrective Lens Shape
Myopia	In front of the retina	Concave (Diverging)
Hypermetropia	Behind the retina	Convex (Converging)
Presbyopia	Behind the retina	Bifocal Lens

How Prisms Create the Spectrum

A glass prism has a unique shape that causes light to bend differently than a flat glass slab. Unlike a rectangular slab, the sides of a glass prism are inclined at an angle called the angle of prism.

The Magic of Dispersion

Dispersion Defined: The splitting of white light into seven distinct colors.
VIBGYOR: The colors always appear in the order of Violet, Indigo, Blue, Green, Yellow, Orange, and Red.
Speed of Light: Different colors travel at different speeds in glass, which is why they spread out.
Recombination: Isaac Newton showed that if you use an inverted second prism, the colors turn back into white light.

Natural Rainbow Formation

A rainbow is a beautiful result of dispersion, refraction, and internal reflection within water droplets. Each raindrop acts as a tiny prism that breaks up sunlight. You will always find a rainbow in the direction opposite to the sun.

Check out: CBSE Class 10th Previous Year Papers

Effects of Our Earth's Atmosphere

The atmosphere isn't a solid block; it has layers of varying densities and temperatures. This leads to "Atmospheric Refraction," which causes several optical tricks.

Seeing Stars and Planets

Twinkling Stars: Stars are very far away. As their light passes through shifting air layers, their apparent position and brightness flicker.
Stationary Planets: Since planets are closer and appear as larger discs, the flickering from different points cancels out, so they don't twinkle.
Apparent Position: Refraction makes stars look slightly higher in the sky than their actual physical location.

The 4-Minute Daylight Gain

Refraction gives us a bit more sunlight every single day:

Early Sunrise: We see the sun 2 minutes before it actually hits the horizon.
Late Sunset: The sun stays visible for 2 minutes after it has physically set.
Sun Shape: The sun's disc looks slightly oval or flattened during these times.

Scattering and the Tyndall Effect

When light hits tiny particles like dust, smoke, or water molecules, it spreads out. This is why the sky has color. Human eye class 10 notes in hindi and English both highlight these concepts for board exams.

The Path of Light

The Tyndall Effect is the scattering of light by particles in a colloid. You can see this when a beam of sunlight enters a dark, dusty room or travels through a thick forest.

Colors in Our World

Why is the sky blue? Small air molecules scatter blue light (short wavelength) much more than red light.
Why is the sun red at sunset? Light travels through a thicker layer of air. Most blue light is scattered away, leaving only the red to reach you.
Space is Black: In space, there is no air to scatter light. This is why astronauts see a black sky even during the day.
Danger Signals: Red is used for danger because it scatters the least, making it visible even through fog or smoke.