CBSE Notes Class 10 Science Chapter 10 - The Human Eye and The Colourful World

CBSE Notes Class 10 Science Chapter 10 – The Human Eye and The Colourful World explains the fascinating link between light, vision, and natural optical phenomena. This CBSE Class 10 Science Notes Chapter covers the structure and functioning of the human eye, accommodation, defects of vision and their correction, along with dispersion and scattering of light. Concepts such as the blue colour of the sky, twinkling of stars, and formation of rainbows are explained using scientific principles frequently tested in the CBSE board examination.

These CBSE human eye class 10 notes are structured to simplify complex physics concepts using exam-focused language, accurate definitions, and logical flow aligned with the latest CBSE syllabus. Designed for conceptual clarity and revision efficiency, human eye and colourful world class 10 notes help reinforce numerical problem-solving, diagram-based questions, and assertion-reason formats frequently asked in CBSE examinations.

1.0Download CBSE Notes for Class 10 Science Chapter 10: The Human Eye and The Colourful World - Free PDF!!

Download CBSE Notes for Class 10 Science Chapter 10: The Human Eye and The Colourful World – Free PDF to learn vision defects, refraction, dispersion, scattering of light, and atmospheric phenomena with clear explanations, diagrams, and exam-focused points for fast revision.

2.0The Human Eye                                              

Structure of Eye

• Cornea: The eye’s front is covered by a transparent, spherical membrane called the cornea.
• Aqueous Humour: A liquid filling the space behind the cornea.
• Iris: A dark, muscular diaphragm behind the cornea with a central opening called the pupil. It regulates light entry by adjusting the pupil size.
• Pupil: Appears black because it does not reflect light.
• Lens: A convex lens made of transparent, jelly-like protein material. It is firm in the centre and softer at the edges, held in place by ciliary muscles.
• Ciliary Muscles: Adjust the lens’s curvature and focal length.
• Retina: The inner back surface of the eye, functioning like a light-sensitive screen. It contains rods and cones which detect light and colour.
• Vitreous Humour: A fluid between the retina and lens.
• Vision Process: Light enters through the cornea and pupil, is focused by the lens to form an inverted image on the retina. Rods and cones in the retina convert this light into electrical signals.
• Optic Nerve: Transmits these electrical signals to the brain, which interprets them.
• Colour Vision: Cones in the retina enable colour vision and are active in bright light. In low light, only rods function, impairing colour perception.

3.0Power of Accommodation

The power of accommodation refers to the eye's ability to adjust the lens's focal length to maintain clear focus on objects at varying distances.

• Accommodation of the Eye: The process by which the ciliary muscles modify the focal length of the eye's lens to focus on objects at various distances..
• Power of Accommodation: The eye's capability to focus on objects at various distances by altering the lens's focal length.
• Range of Vision: The distance between the nearest point of clear vision (near point) and the farthest point of clear vision (far point).
• For a typical human eye, the near point is roughly 25 cm away, which is the shortest distance at which the eye can clearly focus on an object without straining.

4.0Defects of Vision and Correction

1. Myopia (Near-Sightedness)-Difficulty seeing distant objects clearly or the eye is not able to see distant objects clearly.
2. Hypermetropia (Far-Sightedness)-Difficulty focusing on nearby objects or an eye defect in which distant vision is clear while near vision is blurred. In the case of a normal eye the rays of light from the object fall on the eye and converge on the retina but in the case of a hypermetropic eye the light rays are focused behind the retina
3. Presbyopia-Age-related loss of near vision or Presbyopia occurs when the centre of the eye's lens becomes rigid, impairing its ability to focus on close objects.. This condition generally affects almost everyone over the age of 50 - even those with myopia.

Note-These defects can be corrected with appropriate spherical lenses, which help restore clear vision.

5.0Refraction of Light through a Prism

When a beam of white light enters a prism through one of its faces, it bends or refracts toward the base of the prism. This bending happens because the light slows down as it moves from the less dense air into the denser material of the prism.

6.0Dispersion Through a Prism

• The occurrence where white light is separated into its component colours is known as the dispersion of light.
• The wavelengths of different colours of light are different and the refractive index of glass is different for different wavelengths. Higher the wavelength, lower will be the refractive index and thus, lower will be the deviation and vice-versa. Thus, the deviation of red light is low as its wavelength is large. Deviation of violet light is high as its wavelength is small.

7.0Atmospheric Refraction

• The refraction of light produced by the Earth's atmosphere occurs because the refractive index of air varies across different layers.
• Atmospheric refraction takes place due to gradually changing refractive index of the air.

1. Twinkling of Stars

• Luminous energy reaching our eyes per second from the star increases and decreases.
• Apparent position of a star is slightly higher than its actual position when it is viewed from the earth’s surface with time.
• This apparent position is not stationary but it changes with time because of variable physical condition of the refracting medium

2. Advance Sunrise and Delayed Sunset

• The sun appears visible before the actual sunrise and after the actual sunset due to atmospheric refraction.
• The sun seems to be above the horizon even though it is actually just below it due to atmospheric refraction.
• The apparent shift in the sun's position is approximately ½°, which results in a time difference of about 2 minutes between the actual and apparent sunrise.

8.0Scattering of Light 

The process in which the light rays are deflected by the particles of the medium through which they pass is called scattering of light.

Tyndall Effect

• The scattering of light as it passes through a medium containing small particles is called the Tyndall effect.
• When light passes through smoke, the particles in the smoke scatter the light, making the path of the light visible.

Colour of the Clear Sky - Blue

Air molecules and fine particles in the atmosphere, which are smaller than the wavelength of visible light, scatter shorter wavelengths like blue light more effectively than longer wavelengths such as red light. Since blue light has a shorter wavelength and is scattered more, it is predominantly what we see when looking at the sky.

9.0
Detailed CBSE Class 10 Science Chapter 10 – Key Notes

Components and structure

Cornea
Thin transparent protective membrane visible from the outside.

Sclera or sclerotic
The outermost covering of eye and it is made of white fibrous tissue. It is tough so that it can protect the interior of the eye from accidents.

Aqueous humour
Liquid between Cornea and Crystalline lens.

Vitreous humour
Space between lens and the 'Retina' is filled with this liquid.

Iris
It is a muscular diaphragm, which gives distinctive colour to the eye.

Role of iris

• Iris controls the size of the pupil.
• When the light is very bright, iris contracts the pupil and the pupil becomes very small, thus, only a small amount of light enter into the eye.
• In low intensity of light, iris expands the pupil to allow more light to enter into the eye.

Eye lens
A fibrous, jelly like material which is hard in the middle and soft at the edges.

Choroid
A grey membrane attached to sclera.

Ciliary muscles
The curvature of the lens is altered by the 'Ciliary muscles' to which it is attached.

Distant Object

[Image]

01 → Parallel light rays reach eye
02 → Cornea refracts light rays
03 → Ciliary muscle relaxes, Lens flattens
04 → Suspensory ligament under maximum tension

Near Object

[Image]

01 → Diverging light rays strike eye
02 → Cornea refracts light rays
03 → Ciliary muscle contracted
04 → Suspensory ligament loose, Lens thickened

Retina

A delicate membrane having enormous number of light sensitive cells.

Image is formed on retina.

Image is real and inverted.

There are two kind of cells -

Cones
Cones are responsible for color vision.

Rods
Rods are responsible for vision at low light levels.

Blind spot
Image formed at this spot is not visible.

Optic nerves
It transmit the information to the brain.

Power of Accommodation

The ability or property of the eye to change the shape of lens so as to see the object clearly is called 'accommodation'.

Near point
The nearest point for which the image can be formed clearly on the retina.

Least distance of distinct vision
The minimum distance at which objects can be seen clearly without strain.

For young adult – 25 cm
For a child of 7 to 8 year – 7 to 8 cm
For old man of 60 year – 200 cm

Far point
The farthest point up to which the eye can see objects clearly.

For normal eye, far point is at infinity.

Normal Eye

Colour blindness

The defect of eye due to which a person cannot distinguish between colours is called 'colour blindness'.

Colour blind persons cannot distinguish between red, blue and green colours.

Cataract

• The crystalline lens of some people in old age becomes hazy or even opaque due to development of membrane over it.
• Cataract can be removed by performing surgery to restore clear vision.

Defects of Vision and their Correction

Myopia (Nearsightedness)

Some persons can see near objects clearly but cannot see distant objects so clearly.

In this defect nearby objects are clearly visible but distant object are not clearly visible.

Far point of eyes is closer than infinity.

Reason

High converging power of the lens (Ciliary muscles are not relaxed).

Excessive curvature of the cornea.

Elongation of eye-ball.

Correction of defect

To remove this defect diverging lens (concave lens) is used.

Hypermetropia (far sightedness)

Some persons cannot see near objects clearly but they can see distant objects quite well.

Reason

The focal length of the eye lens is too great or eye ball becomes too short.

In this defect distant objects are clearly visible but near by object are not clearly visible.

Near point of eye is shifted away from the eye.

Correction of defect

To remove this defect converging lens (convex lens) is used.

Presbyopia

The defect that arises due to ageing in which a person cannot read comfortably and distinctly without corrective eye glasses is called 'presbyopia'.

Reason: The power of accommodation of the eye decreases with ageing.

Correction of defect: The defect can be corrected with converging lens.

Important Point

Sometimes, a person may suffer from both myopia and hypermetropia.

Such people often use bifocal lens.

Commonly, the upper portion of bifocal lens is a concave lens (used for distant vision) and the lower portion is a convex lens (used for reading purpose).

Triangular prism (Prism)

A triangular cross-section piece of glass called a prism.

Refraction of Light through a Prism

Refraction of light through a prism

Angle of deviation

The angle between the incident ray and the emergent ray is called 'angle of deviation'.

Dispersion of White Light

White light is composed of seven different colors.

Dispersion of white light

• The phenomenon of splitting up of white light into its constituent colours is called 'dispersion of light'.
• When white light travels through a prism, a rainbow-like pattern appears on the other side. This effect is called dispersion.
• Dispersion is a method of demonstrating that white light is composed of many different colours (wavelengths) of light.
• Ice crystals, diamonds, raindrops, etc. also shows dispersion.

Natural Phenomenon

Rainbow

• The rainbow is the nature's most spectacular display of the spectrum of white light.

Formation of the rainbow

• After rain, there are many tiny droplets of water still in the air.
• Sunlight falls on these water droplets.
• These droplets act as tiny prisms.
• When sunlight falls on these droplets, the rays get refracted, then internally reflected and then refracted again.
• Due to this different colours of sunlight are bent at different angles and we are able to see a spectrum in the form of a rainbow.
• Violet ray emerges at an angle of 40° relative to incoming sunlight.
• Red light emerges at an angle of 42°. For other colours, angles lies in between these two values.
• We can see all the seven colours of rainbow in a hollow circular arc which is making an angle of 40° and 42° at our eye.

Atmospheric Refraction

• The refraction of light caused by the earth's atmosphere due to variable refractive index of air at different zones is called 'atmospheric refraction'.

Twinkling of stars

• Atmospheric refraction takes place due to gradually changing refractive index of the air.
• Luminous energy reaching our eyes per second from the star increases and decreases with time.

[Image]

Star appears slightly higher than its actual position

Apparent position of star

• Apparent position of star is slightly higher than its actual position when it is viewed from the earth's surface.
• This apparent position is not stationary but it changes with time because of variable physical condition of the refracting medium.

Why do planets not twinkle?

• The apparent size of stars is very small as compared to apparent size of planets. The star may be considered as a 'point sized' source of light and the planet as an 'extended source' of light.

Delayed sunset and advanced sunrise

• The sun is visible before actual sunrise and after actual sunset because of atmospheric refraction.
• The sun appears to be raised above the horizon when it is slightly below the horizon.

• The apparent shift in the direction of sun is about ½° and corresponding time difference between actual and apparent sunrise is about 2 minutes.

Scattering of light

• The process in which the light rays are deflected by the particles of the medium through which they pass is called scattering of light.

Tyndall effect

• The scattering of light as it passes through a medium containing small particles is called 'Tyndall effect'.
• When sunlight passes through a canopy of a dense forest, tiny water droplets present in the air scatter the light.

• At the sunrise or sunset, the sun is near the horizon.
• Light reaching the eye of an observer travels a larger distance through the atmosphere.
• Most of the blue light and shorter wavelength rays are scattered away by the air particles.
• The light that reaches the eye of an observer is of longer wavelength (of red end).

Sun looks white at noon

• At the noon, the light has to travel a comparatively shorter distance.
• Only a very little amount of blue or violet light is scattered away.

Clouds are generally white

• The larger particles like dust and water drops scatter light of all colour, almost equally and all the colours reach our eyes equally and combine to form white light.

10.0Benefits of CBSE Class 10 Science Chapter 10 - The Human Eye and The Colourful World

• Understand the scattering of light: You'll learn about the Tyndall effect and Rayleigh scattering, which explain why the sky appears blue and the sun reddish at sunrise and sunset.
• Connect physics to everyday observations: The CBSE Notes chapter helps you understand the science behind many natural optical phenomena you observe daily.
• Develop analytical skills: Understanding these concepts requires applying principles of optics to real-world situations.
• Enhance scientific literacy: You'll gain a deeper appreciation for the physics governing light and vision, contributing to your overall scientific understanding.

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