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

NCERT Solutions for Class 10 Science is a beneficial solution guide designed with the intention of approaching the students to clear doubts and concepts. NCERT Solutions for Class 10 Science approaches students in a student-friendly way and is loaded with questions, activities, and exercises that are board and competitive exam-oriented. NCERT Solutions for Class 10 science is the contribution by the teaching faculties having vast teaching experience. NCERT Class 10 Science Solutions makes sure that the answers are student-friendly and is easily understood in a single go. It is developed keeping in mind the concept-based approach along with the precise answering method for examinations. Refer NCERT Solutions for Class 10 for best score in board and competitive exams. It is made available in both web and PDF format for the ease of access.

NCERT Solutions for Class 10 Science Chapter 11 – Summary:

  • The ability of the eye to focus on both near and distant objects, by adjusting its focal length, is called the accommodation of the eye.
  • The smallest distance, at which the eye can see objects clearly without strain, is called the near point of the eye or the least distance of distinct vision. For a young adult with normal vision, it is about 25 cm.
  • The common refractive defects of vision include myopia, hypermetropia and presbyopia. Myopia (short-sightedness – the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power.
  • Hypermetropia (far-sightedness – the image of nearby objects is focussed beyond the retina) is corrected by using a convex lens of suitable power. The eye loses its power of accommodation at old age.
  • The splitting of white light into its component colours is called dispersion.
  • Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset

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NCERT Solution for CBSE Class 10 Science Chapter 11 The Human Eye and Colourful Part 1
NCERT Solution for CBSE Class 10 Science Chapter 11 The Human Eye and Colourful Part 2
NCERT Solution for CBSE Class 10 Science Chapter 11 The Human Eye and Colourful Part 3
NCERT Solution for CBSE Class 10 Science Chapter 11 The Human Eye and Colourful Part 4
NCERT Solution for CBSE Class 10 Science Chapter 11 The Human Eye and Colourful Part 5
NCERT Solution for CBSE Class 10 Science Chapter 11 The Human Eye and Colourful Part 6

 

Access Answers of Science NCERT class 10 Chapter 11: The Human Eye and Colourful World

In text Question Set 1 Page No: 190

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

Answer

The ability of the lens of the eye to adjust its focal length to clearly focus rays coming from distant as well from a near objects on the retina, is known as the power of accommodation of the eye.

2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of corrective lens used to restore proper vision?

Answer

An individual with a myopic eye should use a concave lens of focal length 1.2 m so that he or she can restore proper vision.

3. What is the far point and near point of the human eye with normal vision?

Answer

The minimum distance of the object from the eye, which can be seen distinctly without strain is called the near point of the eye is. For a normal person’s eye, this distance is 25 cm.

The far point of the eye is the maximum distance to which the eye can see objects clearly. The far point of a normal person’s eye is infinity.

4. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Answer

The student is suffering from short-sightedness or myopia. Myopia can be corrected by the use of concave or diverging lens of an appropriate power.

 

Exercise Questions Page Number 197

1. The human eye can focus 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

(b) accommodation

Due to accommodation the human eye can focus objects at different distances by adjusting the focal length of the eye lens.

In text Question Set 3 Page No: 198

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

(a) cornea

(b) iris

(c) pupil

(d) retina

Answer

(d) retina

The retina is the layer of nerve cells lining the back wall inside the eye. This layer senses light and sends signals to the brain so you can see.

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

Answer

(c) 25 cm

25 cm is the least distance of distinct vision for a young adult with normal vision.

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

Answer

(c) ciliary muscles

The action of the ciliary muscles changes the focal length of an eye lens

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?

Answer

The power (P) of a lens of focal length f is given by the relation

Power (P) = 1/f

(i) Power of the lens (used for correcting distant vision) = – 5.5 D

Focal length of the lens (f) = 1/Pf= 1/-5.5 = -0.181 m

The focal length of the lens (for correcting distant vision) is – 0.181 m.

(ii) Power of the lens (used for correcting near vision) = +1.5 D

Focal length of the required lens (f) = 1/P

f = 1/1.5 = +0.667 m

The focal length of the lens (for correcting near vision) is 0.667 m.

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?

Answer

The individual is suffering from myopia. In this defect, the image is formed in front of the retina. Therefore, a concave lens is used to correct this defect of vision.

Object distance (u) = infinity = ∞

Image distance (v) = – 80 cm

Focal length = f

According to the lens formula,

ncert solution class 10 chapter 11 fig 1

A concave lens of power – 1.25 D is required by the individual to correct his defect.

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.

Answer

An individual suffering from hypermetropia can see distinct objects clearly but he or she will face difficulty in clearly seeing objects nearby. This happens because the eye lens focuses the incoming divergent rays beyond the retina. This is corrected by using a convex lens. A convex lens of a suitable power converges the incoming light in such a way that the image is formed on the retina, as shown in the following figure.

ncert solution class 10 chapter 11 fig 2

The convex lens creates a virtual image of a nearby object (N’ in the above figure) at the near point of vision (N) of the individual suffering from hypermetropia.

The given individual will be able to clearly see the object kept at 25 cm (near point of the normal eye), if the image of the object is formed at his near point, which is given as 1 m.

Object distance, u= – 25 cm

Image distance, v= – 1 m = – 100 m

Focal length, f

Using the lens formula,

ncert solution class 10 chapter 11 fig 3

A convex lens of power +3.0 D is required to correct the defect.

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

Answer

A normal eye is not able to see the objects placed closer than 25 cm clearly because the ciliary muscles of the eyes are unable to contract beyond a certain limit.

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

Answer

The image is formed on the retina even on increasing the distance of an object from the eye. For this eye lens becomes thinner and its focal length increases as the object is moved away from the eye.

10. Why do stars twinkle?

Answer

The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. The atmospheric refraction occurs in a medium of gradually changing refractive index.

11. Explain why the planets do not twinkle?

Answer

Unlike stars, planets don’t twinkle. Stars are so distant that they appear as pinpoints of light in the night sky, even when viewed through a telescope. Because all the light is coming from a single point, its path is highly susceptible to atmospheric interference (i.e. their light is easily diffracted).

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

Answer

White light coming from the sun has to travel more distance in the atmosphere before reaching the observer. During this, the scattering of all coloured lights except the light corresponding to red colour takes place and so only the red coloured light reaches to the observer. Therefore the sun appears reddish at sunrise and sunset.

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

Answer

The sky appears dark instead of blue to an astronaut, as scattering of light does not take place outside the earth’s atmosphere.

NCERT Solutions for class 10 Science Chapter 11: The Human Eye and Colourful World

NCERT Class 10 Science Chapter 11 describes the fine structure of the human eye. It does explain the reason behind the color of the sun during the time of sunrise and sunset. It explains the accommodation of the eye concept. Various defects that occur to the eye like refractive defects of vision which include hypermetropia, myopia, and presbyopia are discussed in NCERT Solutions. It describes the near point of the eye or the least distance of distinct vision. Topics included in this chapter are:

  • Atmospheric refraction
  • The human eye (4 questions)
  • Scattering of light
  • Refraction of light through a prism
  • Dispersion of white light by a glass prism
  • Post chapter exercise (13 questions)

Exercise 11.1 solution

NCERT Solutions for class 10 Science Chapter 11: The Human Eye and Colourful World

  • NCERT solutions for class 10 explains the detailed structure of the human eye.
  • Explains the various defects that happen for human and also describes the ways to correct it.
  • Dispersion of light concept is made understandable in a simple way.
  • It also explains the reason for the sky being blue along with the color of the sun at sunset and sunrise events.

Key features of NCERT Solutions for class 10 Science Chapter 11: The Human Eye and Colourful World

  • The simple and easily understandable approach is followed in NCERT solutions to make students aware of topics.
  • NCERT Solutions offer detailed answers to all the questions to help students in their preparations.
  • It is useful for successfully clearing the CBSE board exams in flying colors and is also the best guide for Science Olympiads, and other competitive exams.
  • Provides completely solved solutions to all the questions present in the respective NCERT textbooks.

Frequently Asked Questions on The Human Eye and Colourful World

What is meant by power of accommodation of the eye ?

The ability of the lens of the eye to adjust its focal length to clearly focus rays coming from distant as well from a near objects on the retina, is known as the power of accommodation of the eye.

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

The image is formed on the retina even on increasing the distance of an object from the eye. For this eye lens becomes thinner and its focal length increases as the object is moved away from the eye.

Why do stars twinkle ?

The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. The atmospheric refraction occurs in a medium of gradually changing refractive index.

Explain why the planets do not twinkle ?

Unlike stars, planets don’t twinkle. Stars are so distant that they appear as pinpoints of light in the night sky, even when viewed through a telescope. Because all the light is coming from a single point, its path is highly susceptible to atmospheric interference (i.e. their light is easily diffracted).

Why does the Sun appear reddish early in the morning ?

White light coming from the sun has to travel more distance in the atmosphere before reaching the observer. During this, the scattering of all coloured lights except the light corresponding to red colour takes place and so only the red coloured light reaches to the observer. Therefore the sun appears reddish at sunrise and sunset.

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

The sky appears dark instead of blue to an astronaut, as scattering of light does not take place outside the earth’s atmosphere.

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