NCERT Solutions for Class 10 Science Chapter 11 Human eye and colorful world intext questions on Page 190 and chapter end Exercises in English Medium. Download Solutions in Hindi Medium updated for new academic session 2022-2023.

NCERT Solutions for Class 10 Science Chapter 11

• 10th Science Chapter 11 Answers in PDF Format

These solutions are applicable for UP Board High School students also. Download here the UP Board Solutions for Class 10 Science Chapter 11 in Hindi Medium. Important and Extra Questions based on Chapter 11 of 10th Science are also given with proper answers. All NCERT Solutions and Offline Apps are free to download or use online without downloading. Solutions are available online as well as offline in PDF form to free download. Download NCERT Solutions 2022-2023 and Offline Apps for class x other subjects also. NCERT Solutions and all the study material on Tiwari Academy is free to use without any login or password.

 Class: 10 Science (English and Hindi Medium) Chapter 11: Human eye and colorful world

10th Science Chapter 11 Answers in English & Hindi Medium

Class 10 Science Physics Chapter 11 Human eye and colorful world intext questions given on page 190 Answers and chapter end exercises answers are given below in updated form for new academic session 2022-23. Download UP Board Solutions for Class 10 Science Chapter 11 with important Questions and intext questions in Hindi and English. Visit to Discussion Forum to ask your doubts and discuss the facts asked by other uses.

What is hypermetropia? What are the two causes of this defect of vision? How can this defect of the eye be corrected?

Hypermetropia or long-sightedness: It is a vision defect in which a person can see the distant object clearly but cannot see the nearby objects clearly.
Cause of hypermetropia: This defect arises due to either of the following two reasons:
(i) The eyeball becomes too small along its axis so that the distance between the eye lens and the retina is reduced.
(ii) The focal length of the eye lens becomes too large resulting in the low converging power of the eye lens.
Correction of hypermetropia: A hypermetropia eye is corrected by using a convex lens of suitable focal length. This lens diverges the rays such that the rays coming from normal near point N appear to come after refraction, from near point N’ of the defected eye. That is a virtual image of the object placed at N is formed at N’. Then the eye lens forms a clear image at the retina.

What is presbyopia? Write two causes of this defect.

Presbyopia: this defect is similar to hypermetropia i.e., a person having this defect cannot see nearby objects distinctly, but can see distant objects without any difficulty. This defect differs from hypermetropia in the cause by which it is produced. It usually occurs in elderly persons. Due to the stiffening of the ciliary muscles, the eye lens loses flexibility and hence the accommodating power of the eye lens decreases.

“Stars appear higher than they actually are.” Give reason.

Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position. The stars appear slightly higher (above) than their actual position when viewed near the horizon.

Why is the colour of the clear sky blue? Explain.

The blue colour of the sky is due to the scattering of the sunlight by the molecules of the atmosphere. The molecules of air, such as N2 and O2, have sizes smaller than the wavelength of visible light. As sunlight passes through the atmosphere, these molecules absorb some amount of sunlight and re-emit it. They scatter blue light of shorter wavelength more strongly than red light of longer wavelength. When we look at the sky, the scattered light enters our eyes and this light contains blue light in a larger proportion. This is why, the sky appears blue.

Questions for Practice

Question 1:
What is myopia? State two reasons due to which this defect is caused.
Answer 1:
Myopia or short-nearsightedness: It is a vision defect in which a person can see nearby objects clearly but cannot see the distant objects clearly beyond a certain point. This defect is common among children.
Cause of Myopia: This defect arises due to either of the following two reasons:
(i) The eyeball gets elongated along its axis so that the distance between the eye lens and the retina becomes larger.
(ii) The focal length of the eye lens becomes too short due to the excessive curvature of cornea.
Correction of Myopia: A myopia eye is corrected by using a concave lens of focal length equal to the far point F from the eye. This lens diverges the parallel rays from distant object as if they are coming from the far point F. Finally, the eye lens forms a clear image at the retina.

Question 2:
What will be the colour of sky in the absence of atmosphere? or “The sky appears dark to passengers flying at very high altitudes.” Give reason.
Answer 2:
In the absence of any atmosphere, there will be no scattering of sunlight and the sky will appear dark. The sky appears dark to passengers or astronauts flying at high altitudes, as scattering is not prominent at such heights due to thin atmosphere.

Questions from Board Papers

Question 1:
Why do we see stars appear twinkling, whereas planets do not twinkle?
or
A star sometimes appears brighter and some other times fainter. What is this defect called? State reason for this effect.

Answer 1:
Twinkling of stars: The apparent position of a star is slightly different from the actual position due to refraction of starlight by the atmosphere. Further, this apparent position is not stationary but keeps on changing due to the change in atmospheric conditions like density, temperature, etc. the path of the rays of light coming from the stars goes on varying slightly. The amount of light entering our eyes from a particular star increases or decreases randomly with time. Sometimes, the star appears bright and other times, it appears fainter. This gives rise to the twinkling effect of the star.

The planets do not show twinkling effect: As the planets are much closer to the earth, the amount of light received from them is much greater and the fluctuations caused in the amount of light due to atmospheric refraction are negligible as compared to the amount of light received from them.

Question 2:
What is astigmatism? How is it caused? How is it corrected? Or What is astigmatism and how is this vision defect counteracted?

Answer 2:
Astigmatism: It is a defect of vision in which a person cannot simultaneously see both the horizontal and vertical views of an object with same clarity.
Cause of astigmatism: This defect occurs when the cornea of the eye is not perfectly spherical. This results in objects in one direction being well focussed while those in perpendicular direction are not well focussed.

Correction of astigmatism: Astigmatism can be corrected by using cylindrical lenses. They have different curvatures in horizontal and vertical directions and so they can be oriented suitably to compensate for the irregularities in the cornea.

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

Since the size of eyes cannot increase or decrease, the image distance remains constant. When we increase the distance of an object from the eye, the image distance in the eye does not change. The increase in the object distance is compensated by the change in the focal length of the eye lens. The focal length of the eyes changes in such a way that the image is always formed at the retina of the eye.

Why do stars twinkle?

Stars emit their own light and they twinkle due to the atmospheric refraction of light. Stars are very far away from the earth. Hence, they are considered as point sources of light. When the light coming from stars enters 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 comes more towards us, it appears brighter than when it comes less towards us. Therefore, it appears as if the stars are twinkling at night.

Explain why the planets do not twinkle?

Planets do not twinkle because they appear larger in size than the stars as they are relatively closer to earth. Planets can be considered as a collection of a large number of point-size sources of light. The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.

Why does the Sun appear reddish early in the morning?

During sunrise, the light rays coming from the Sun have to travel a greater distance in the earth’s atmosphere before reaching our eyes. In this journey, the shorter wavelengths of lights are scattered out and only longer wavelengths are able to reach our eyes. Since blue colour has a shorter wavelength and red colour has a longer wavelength, the red colour is able to reach our eyes after the atmospheric scattering of light. Therefore, the Sun appears reddish early in the morning.

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

The sky appears dark instead of blue to an astronaut because there is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reach the eyes of the astronauts and the sky appears black to them.

What is meant by power of accommodation of the eye?

When the ciliary muscles are relaxed, the eye lens becomes thin, the focal length increases, and the distant objects are clearly visible to the eyes. To see the nearby objects clearly, the ciliary muscles contract making the eye lens thicker. Thus, the focal length of the eye lens decreases and the nearby objects become visible to the eyes. Hence, the human eye lens is able to adjust its focal length to view both distant and nearby objects on the retina. This ability is called the power of accommodation of the eyes.

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

The near point of the eye is the minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal human eye, this distance is 25 cm. The far point of the eye is the maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity.

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?

A student has difficulty in reading the blackboard while sitting in the last row. It shows that he is unable to see distant objects clearly. He is suffering from myopia. This defect can be corrected by using a concave lens.

Is chapter 11 of class 10th Science interesting to learn?

Yes, chapter 11 of class 10th Science is very interesting. Students will study many interesting topics in this chapter. Topics which students study in chapter 11 are:

• 1. The Human Eye
• 2. Power of Accommodation
• 3. Defects of vision and their correction
• 4. Myopia
• 5. Hypermetropia
• 6. Presbyopia
• 7. Refraction of light through a prism
• 8. Dispersion of white light by a glass prism
• 9. Atmospheric refraction
• 10. Twinkling of stars
• 11. Advance sunrise and delayed sunset
• 12. Scattering of light
• 13. Tyndall Effect
• 14. Why is the color of the clear Sky Blue?
• 15. Colour of the Sun at Sunrise and Sunset.

How many days are needed to complete chapter 11 of class 10th Science?

Students need a maximum of 8-10 days to complete chapter 11 (The Human Eye and The Colourful World) of grade 10th Science if they give 2 hours per day to this chapter. This time is an approximate time. This time can vary because no students can have the same working speed, capability, efficiency, etc.

How many activities are there in chapter 11 of grade 10th Science?

There are 3 activities in chapter 11 of grade 10th Science. All the activities are nice, interesting, and logical. These activities help students to understand the chapter easily and practically. Students enjoy doing these activities in school.

Is chapter 11 of grade 10th Science important for the board exams?

Yes, chapter 11 of grade 10th Science is important from the exam point of view. Every year questions come from chapter 11 in the exams. There are 17 questions in chapter 11. All the questions of this chapter are significant and can come in the exams. This chapter is not very lengthy and not very short.