NCERT Solutions Class 10 Science Chapter 11

NCERT Solutions Class 10 Science Chapter 11: Human Eye and Colourful World

Class 10 Science Chapter 11 is about the Human eye and the colorful world. The human body is a complex structure constructed in levels from the smallest cells to tissues, organs, and organ systems. The human eyes are the most sensitive and valuable sense organs. It enables us to see the colorful world around us. 

The idea of nature, position, and relative size of images formed by lenses studied in the previous chapter, Refraction of light by lenses, is crucial to understanding this chapter on human eyes and the colorful world. 

Extramarks website helps students score well in their board examinations and many other entrance examinations. Many students suffer due to a lack of clarification at the right time and get low grades in their examinations. Extramarks NCERT Solutions Class 10 Science Chapter 11 are prepared by Science subject matter experts with years of teaching experience who meticulously follow the NCERT textbooks and CBSE guidelines to provide authentic and reliable study material to the students

Concepts like the Power of Accommodation, Defects of Vision and their Correction, Refraction of Light through a Prism, etc., are easy to understand and learn with NCERT Solutions Class 10 Science Chapter 11.

The latest term-wise CBSE Syllabus 2021-2022 ensures that the chapters are suitable for the students to progress in their respective streams. Referring to and practicing thoroughly with NCERT solutions can help students to get a thorough understanding of the chapter to deal with their class assignments, tests, and exams. 

Millions of students have benefitted from the Extramarks platform for studying and preparing for their examinations and have come out with flying colors. Extramarks provide comprehensive study materials which are accurate and reliable and students have complete trust and faith in  NCERT solutions, chapter notes, revision notes, important questions, and their solved answers, etc. These easy-to-understand simplified notes help you to understand complex topics which are graded and it becomes easier to get the hang of the topic in higher classes. It’s good to build a strong foundation to get excellent grades year after year.

Key Topics Covered In NCERT Solutions Class 10 Science Chapter 11

Chapter 11 Science Class 10 is about ’The Human Eye and the Colourful World’. Extramarks NCERT Solutions Class 10 Science Chapter 11 provides a detailed explanation of the structure of the Human Eye. 

A few of the important topics covered in this chapter are given below. Students should refer to our NCERT solutions to step up their learning and stay focused on their goals. :

 The Human Eye:

Structure of the Human Eye:

The human eye is about 2.3 cm in diameter and filled with fluid.  The main parts of the human eye are:

  1. Sclera: The tough protective white part and the eye’s outer covering.
  2. Cornea: The cornea is the front transparent part of the sclera, through which light enters the eye.
  3. Iris: A ring-like, dark, muscular tissue behind the cornea is known as the iris. The iris’s colour specifies the eye’s colour and helps adjust exposure by adjusting the iris.
  4. Pupil: A small opening in the iris helps regulate the amount of light that enters the eye. Iris controls the size of the pupil.
  5. Lens: Located behind the Pupil, it is transparent. The lens makes the eye focus on far or near objects. The ciliary muscles surrounding the lens change their shape to focus light on the retina. It relaxes to become thinner to focus on distant objects and contracts to become thicker to focus on nearby objects.
  6. Retina: The retina consists of numerous nerve cells and is a light-sensitive layer. The primary function is to convert images formed by the lens into electrical impulses and transmit these impulses to the brain through optic nerves.
  7. Optic nerves: Optic nerves carry visual messages to the brain. Optic nerves are more than 1 million, and one connects the back of the retina to the brain. 

There are two types of optic nerves:

  • Cones are meant for detailed central and color vision as they are more sensitive to bright light.
  • Rods are more sensitive to dim lights. They are meant for peripheral vision.

Apart from the above, the eye consists of six muscles that provide different tensions and torques to control eye movement. They are the superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique, and superior oblique. 

Blind Spot: 

There is no vision at the optic nerve and retina junction, and there are no sensory nerve cells.

 Functioning of the Human Eye:

The human eye is like a camera in an electronic device that focuses and allows light to produce images. In simple terms, light rays experience refraction, i.e., get diverted from distant objects, pass through various mediums like the cornea, crystalline lens, aqueous humor, the lens, and vitreous humor, and finally land on the retina, forming an image. However, the image is usually inverted and later corrected by the brain. The conversion of light rays to an image is based on the different refractive indexes. 

The functioning of the human eye is an interesting yet complex topic and students will find a detailed explanation about the same in our NCERT Solutions Class 10 Science Chapter 11. 

Power of Accommodation: 

The process where ciliary muscles function to change the focal length of the eyes to form clear images on the retina is considered the power of accommodation of the eyes. In other words, it is the power of the eyes to adjust the focal length far or closer to objects and objects moving away or towards the eyes.

Defects of Vision and their Correctness: 

Defects of vision can be defined as loss of the ability of the eye to adjust its focal length, i.e. defect in the refractive index. Hence a person with this kind of vision impairment cannot see things correctly.

Few of the Refractive Defects of Vision as covered in NCERT Solutions Class 10 Science Chapter 11: 

  • Myopia or near-sightedness: The condition in which a person can see closer objects but cannot see distant objects.

Correction: Using a concave lens of appropriate focal length. 

  • Hypermetropia or farsightedness: The condition in which a person can see distant objects but cannot see closer things. 

Correction: Using a convex lens of appropriate power.

  • Presbyopia: This condition happens with the age factor, especially in people above 40 years, where the power of the eye to adjust the focal length decreases, making it difficult to view nearby objects.
  • Correction: Proper contact lenses or a minor surgery can help rectify the issue.

 Refraction of Light through a Prism:

A prism is made of transparent material like glass and has two flat surfaces to form an acute angle. When light passes through the prism, it slows and bends, but different wavelengths bend at different angles. This separates light into different wavelengths, forming a rainbow of colors. The spectra of visible light that an object reflects determine the color that the thing appears in the human eye. 

The below picture shows how the incident ray PE enters the prism, and the emergent ray appears by the refraction of light (EF). Also, the angle of deviation is calculated by the formula i1+i2=A+delta. 

Dispersion of White light by a Glass Prism:

When white light enters the glass prism at the angle of incidence, it refracts and splits into its component colors, Red, Orange, Yellow, Green, Blue, and Violet, as shown below.

Our  Science subject matter experts have explained the concept of dispersion of white light with a glass prism with real-life applications. Students can experiment at home and get first-hand experience with the same. Many more interesting experiments are given in our NCERT Solutions Class 10 Science Chapter 11. 

Atmospheric Refraction, Scattering of Light:

Earth’s atmosphere-refracting light is known as atmospheric refraction. It is caused by the bending of light rays when they pass through different air layers of the earth’s atmosphere, which are of different optical densities.

Some key  points are: 

  • The atoms of gases and dust particles have different optical densities.
  • The light coming from a star experiences atmospheric refraction due to varying optical densities of air at various altitudes.
  • When an object transmits light rays into the atmosphere with different air layers and densities, the light is refracted by the atmosphere.

 Tyndall Effect:

Tyndall effect is the circumstance in which the particles in a colloid scatter the ray of light pointed at them. All colloidal solutions demonstrate this effect with some very fine deferment. It can be used to check if a solution is a colloid. The strength of scattered light depends on the density of the colloidal particles and the frequency of the incident light.

When a ray of light enters the colloid, the colloidal particles in the solution do not allow the light to pass through entirely. The light hits the colloidal particles and gets scattered by deviating from its standard straight-line path, thus making the light beam visible.

Why is the Colour Sky Blue?

The light emitted by the sun in earth’s atmosphere is scattered in all directions by the atoms of gases and dust particles. As the wavelength of the blue color is shorter than other colors, it spreads more, and the sky appears blue.

Color of Sun at Sunrise and Sunset:

The rays have to travel a more significant part of the atmosphere during sunrise and sunset because they are very close to the horizon. Therefore, light other than red is scattered away by the particles. Most of the red light, the least dispersed, enters our eyes. In other words, the light which reaches our eyes is of longer wavelengths. Hence, the  Sun and the sky appear red at sunrise and sunset.

NCERT Solutions Class 10 Science Chapter 11 – Human Eye and Colourful World provided by Extramarks gives a detailed and easy-to-understand explanation of all the topics presented in this chapter. So once students register on the Extramarks’ website, they need not worry about authentic study material because Extramarks has a one-stop solution for all your problems. The solutions provided by Extramarks are self-explanatory, meaning students may not always depend on teachers to clarify their doubts while studying, especially during last-minute preparation. 

NCERT Solutions Class 10 Science Chapter 11: Exercises &  Solutions

NCERT Solutions Class 10 Science Chapter 11 prepared by Extramarks’ subject matter expert, is a comprehensive guide covering all essential topics from the examination point of view. Students may study using NCERT solutions, including various questions such  as MCQs, short and long answer questions, and much more to nail any tests, and exams and come out with flying colors

Students may refer to and practice different types of questions consolidated in NCERT Solutions Class 10 Science Chapter 11 by clicking on the links given below.

  • NCERT Solutions – Short-answer Questions
  • NCERT Solutions – MCQ’s
  • NCERT Solutions – Long-answer Questions

Furthermore, in addition to NCERT Solutions Class 10 Science Chapter 11- The Human Eye and Colourful World, students may access NCERT solutions for all other chapters. Students may click on the respective links below to refer to NCERT Solutions from Classes 1 to 12.

NCERT Exemplar Class 10 Science Chapter 11

NCERT Class 10 Science Chapter 11-Exemplar Solutions and problems are structured systematically according to the latest CBSE Class 10 Science Syllabus (2021-22). NCERT Exemplar solutions facilitate sound learning of the concepts like power of accommodation, refraction of light through a prism, atmospheric refraction, splitting of white light and blue color of the sky, etc. By practicing these questions thoroughly which, are available on the Extramarks’ website, students become confident in solving those tricky and difficult questions with ease. They may even continue their association with us for the next level too. Students who have signed up with Extramarks have complete faith and trust in Extramarks.   

Chapter 1 Chemical Reactions and Equations
Chapter 2 Acids, Bases and Salts
Chapter 3 Metals and Non-metals
Chapter 4 Carbon and Its Compounds
Chapter 5 Periodic Classification of Elements
Chapter 6 Life Processes
Chapter 7 Control and Coordination
Chapter 8 How do Organisms Reproduce?
Chapter 9 Heredity and Evolution
Chapter 10 Light Reflection and Refraction
Chapter 11 Human Eye and Colourful World
Chapter 12 Electricity
Chapter 13 Magnetic Effects of Electric Current
Chapter 14 Sources of Energy
Chapter 15 Our Environment
Chapter 16

NCERT Solutions Class 10 Science -Exemplar – Question and Answers

Key Features of NCERT Solutions Class 10 Science Chapter 11

The essential features of NCERT Solutions Class 10 Science Chapter 11 include:

  • Our NCERT solutions are structured to present complete and understandable coverage of topics related to daily life.
  • Solutions prepared by the Extramarks give detailed answers to the chapter questions that help students to solve end-text questions and even provide sample question papers to be thorough in their respective subjects.
  • The notes are prepared by highly qualified and experienced faculty who meticulously follow the latest NCERT textbooks to provide authentic and reliable study material to students.  
  • The content on NCERT solutions provided by Extramarks is regularly updated as per the CBSE Board. These handy notes can be utilized for later use also because CBSE board question papers have maximum questions from NCERT only. 

Q.1 The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to

(a) presbyopia.
(b) accommodation.
(c) near-sightedness.
(d) far-sightedness.


Answer: The correct option is (b).
Explanation: Power of accommodation is the ability of eye lens to change its focal length so that the image of an object can be focused on the retina.

Q.2 The human eye forms the image of an object at its

(a) cornea.
(b) iris.
(c) pupil.
(d) retina.


The correct option is (d).
Explanation: In the case of human eye, image is formed at retina.

Q.3 The least distance of distinct vision for a young adult with normal vision is about

(a) 25 m.
(b) 2.5 cm.
(c) 25 cm.
(d) 2.5 m.


The correct option is (c).
Explanation: Least distance of distinct vision is the smallest distance at which the human eye can see the objects clearly without any strain. For a normal eye, it is 25 cm.

Q.4 The change in focal length of an eye lens is caused by the action of the

(a) pupil.
(b) retina.
(c) ciliary muscles.
(d) iris.


The correct option is (c).
Explanation: The curvature of the eye lens can be changed by the relaxation or contraction of ciliary muscles. The change in curvature of the eye lens changes the focal length of the eyes. Thus, the change in focal length of an eye lens is caused by the action of ciliary muscles.

Q.5 A person needs a lens of power – 5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting
(i) distant vision, and
(ii) near vision?


( i )Powerofthe lens used for correcting distance vision= -5.5 Focal length ( f )of the required lens f = 1 P f= 1 -5.5 =-0.181m Hence, the focal length of the lens for correcting distant vision = – 0.181 m.( ii )Powerof the lends used for correcting near vision = +1.5D Focal length (f) of the required lens, f = 1 P f= 1 1.5 D =+0.667m Hence, the focal length of the lens for correcting near vision is 0.667m. MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0le9yqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@C4B3@

Q.6 The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?


Given,u=¥ v=-80cm Onusing lens formula, 1 v 1 u = 1 f 1 80 1 ¥ = 1 f or,f=-80cm=-0.8m Now,P= 1 f( metres ) P= 1 -0.8 =-1.25D. Aconcave lens of power -1.25 D is required by the person to correct the defect. MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0le9yqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeaacaGaaiaabeqaamaabaabaaGceiqabeaay=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@3324@

Q.7 Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.


It is a visual defect in which an eye cannot see the nearby objects clearly. The image of the object, in this case, is formed beyond the retina and hence person experiences difficulty in understanding the object.

This defect of vision can be corrected by using a convex lens. A convex lens of suitable power converges the incoming light in such a way that the image is formed on the retina. The convex lens actually creates a virtual image of a nearby object (o’) at the near point of vision (o) of the person suffering from hypermetropia.
A person can clearly see the object kept at 25 cm, if the image of the object is formed at his near point, which is given as 1 m.

Given,u=-25cm v=-1m=-10cm Onusiglensformula, 1 v 1 u = 1 f 1 -100 1 -25 = 1 f or,f= 100 3 cm=33.3cm=0.33m Now,P= 1 f( metres ) P= 1 0.33m =+3D. Hence,aconvexlensofpower+3Disrequiredtocorrectthedefect. MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0le9yqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@2765@

Q.8 Why is a normal eye not able to see clearly the objects placed closer than 25 cm?


As the ciliary muscles of eyes are incapable to contract beyond a certain limit hence, a normal eye cannot see clearly the objects kept closer than 25 cm. If an object is kept at a distance less than 25 cm from the eye, then the object seems blurred and produces strain in the eyes.

Q.9 What happens to the image distance in the eye when we increase the distance of an object from the eye?


For an eye, the image distance always remains constant as the size of eyes cannot increase or decrease. The increase in the object distance is balanced by the change in the focal length of the eye lens. The eye changes its focal length focal length in such a way that the image is always formed at retina.

Q.10 Why do stars twinkle?


Twinkling of stars is due to the atmospheric refraction of light. As stars are too far from the earth therefore, they can be considered as point sources of light. When the light coming from stars passes through the earth’s atmosphere, it gets refracted at different levels because of the variation in the air density at different levels of the atmosphere. When the star light refracted by the atmosphere, it comes more towards us. It appears brighter when it comes less towards us.

Q.11 Explain why the planets do not twinkle.


Planets do not twinkle like stars because planets are much closer to the earth and are thus seen as extended objects. If we consider planet as a collection of large number of point-sized sources of light, sources of light the variation in amount of light entering our eye from all the individual point sized sources will average out to zero, thereby nullifying the twinkling effect.

Q.12 Why does the Sun appear reddish early in the morning?


During sunrise, the light coming from the Sun has to travel a larger distance in the earth’s atmosphere before entering to our eyes. During this, the shorter wavelengths of lights are scattered out and only longer wavelengths are able to reach our eyes. As blue colour has a shorter wavelength and red colour has a longer wavelength, the red colour reaches to our eyes after the atmospheric scattering of light. Hence, the Sun seems reddish while sunrise.

Q.13 Why does the sky appear dark instead of blue to an astronaut?


There is no atmosphere in the outer space. Due to this, the sunlight does not scatter and hence, no scattered light reaches to the eyes of astronauts in the space and hence, the sky appears black to them.

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