NCERT Exemplar for Class 10 Science Chapter 11 - Human Eye and Colourful World (Book Solutions)

Multiple Choice Questions (MCQs)

1. A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power

(a) + 0.5 D 

(b) – 0.5 D 

(c) + 0.2 D 

(d) – 0.2 D

Ans: (b) -0.5 D

Explanation: This person is suffering from myopia. He needs a concave lens and hence power would be negative.

P =  $\frac{1}{f}$ = $\frac{1}{{2m}}$

$ = 0.5D$

2. A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct? 

(a) The near point of his eyes has receded away 

(b) The near point of his eyes has come closer to him 

(c) The far point of his eyes has come closer to him 

(d) The far point of his eyes has receded away

Ans: (a) The near point of his eyes has receded away 

Explanation: In hypermetropia, the near point of the eye moves away from 25cm. Due to this, the person needs to keep a book at more than 25 cm to read it properly.

3. A prism ABC (with BC as a base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in Figure 11.1. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky?

(i)                                 (ii)                                  (iii)                          (iv)                    

 Fig. 11.1

(a) (i) 

(b) (ii) 

(c) (iii) 

(d) (iv)

Ans: (b) (ii)

Explanation: If the prism is kept with base BC at the bottom, then the emergent band of colour would show violet at the bottom. Violet would be at the top of the prism if it was retained with base BC at the top, followed by indigo and blue.

4. At noon the sun appears white as 

(a) light is least scattered 

(b) all the colours of the white light are scattered away 

(c) the blue colour is scattered the most 

(d) the red colour is scattered the most

Ans: (b) all the colours of the white light are scattered away 

Explanation: Sky will appear dark in case of option ‘a’. It will appear blue in the case of option ‘c’ and will appear red in the case of option ‘d’.

5. Which of the following phenomena of light are involved in the formation of a rainbow? 

(a) Reflection, refraction and dispersion 

(b) Refraction, dispersion and total internal reflection 

(c) Refraction, dispersion and internal reflection 

(d) Dispersion, scattering and total internal reflection

Ans: (c) Refraction, dispersion and internal reflection 

Explanation: White light is separated into its component colours as a result of dispersion. Refraction bends the incident light to an angle that causes internal reflection, and finally, a rainbow is formed.

6. Twinkling of stars is due to atmospheric 

(a) dispersion of light by water droplets 

(b) refraction of light by different layers of varying refractive indices 

(c) scattering of light by dust particles 

(d) internal reflection of light by clouds

Ans: (b) refraction of light by different layers of varying refractive indices 

Explanation: Due to refraction of light by different layers of varying refractive indices, the apparent position of the source of light keeps on changing. Due to this, stars appear to twinkle.

7. The clear sky appears blue because 

(a) blue light gets absorbed in the atmosphere 

(b) ultraviolet radiations are absorbed in the atmosphere 

(c) violet and blue lights get scattered more than lights of all other colours by the atmosphere 

(d) light of all other colours is scattered more than the violet and blue colour lights by the atmosphere

Ans: (c) violet and blue light get scattered more than lights of all other colours by the atmosphere

8. Which of the following statements is correct regarding the propagation of light of different colours of white light in the air? 

(a) Red light moves fastest 

(b) Blue light moves faster than green light 

(c) All the colours of the white light move with the same speed 

(d) Yellow light moves with the mean speed as that of the red and the violet light

Ans: (c) All the colours of the white light move with the same speed

Explanation: Because air is not a dispersive medium, all wavelengths of light travel at the same speed.

9. The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light 

(a) is scattered the most by smoke or fog 

(b) is scattered the least by smoke or fog 

(c) is absorbed the most by smoke or fog 

(d) moves fastest in air

Ans: (b) is scattered the least by smoke or fog

Explanation: The amount of scattering is inversely proportional to the wavelength multiplied by the fourth power. And because the wavelength of red is the longest, the quantity of scattering is reduced.

The colour red is used for warning signals put on the tops of tall buildings or traffic signals so that they may be seen from afar.

10. Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset? 

(a) Dispersion of light 

(b) Scattering of light 

(c) Total internal reflection of light 

(d) Reflection of light from the earth

Ans: (b) Scattering of light 

Explanation: The colour red scatters the least and so goes the greatest distance. Light needs to travel a longer distance to reach us at sunset or sunrise. As a result, only red light reaches humans, giving the sky a crimson hue.

11. The bluish colour of water in deep sea is due to 

(a) the presence of algae and other plants found in water 

(b) reflection of sky in the water 

(c) scattering of light 

(d) absorption of light by the sea 

Ans: (b) Reflection of sky in water

Explanation: Water is colourless. Its colour appears to be the same as the object reflected by it.

12. When light rays enter the eye, most of the refraction occurs at the 

(a) crystalline lens 

(b) outer surface of the cornea 

(c) iris 

(d) pupil

Ans: (b) Outer surface of the cornea

Explanation: The majority of refraction in the eye occurs when light rays pass through the eye's curved, transparent front surface (cornea). The natural (crystalline) lens of the eye bends light rays as well.

13. The focal length of the eye lens increases when eye muscles 

(a) are relaxed and lens becomes thinner 

(b) contract and lens becomes thicker 

(c) are relaxed and lens becomes thicker 

(d) contract and lens becomes thinner

Ans: (a) are relaxes and lens becomes thinner

Explanation: The lens thins out when the muscles are relaxed. As a result, its focus length rises, indicating that option A is correct.

14. Which of the following statements is correct? 

(a) A person with myopia can see distant objects clearly 

(b) A person with hypermetropia can see nearby objects clearly 

(c) A person with myopia can see nearby objects clearly 

(d) A person with hypermetropia cannot see distant objects clearly

Ans: (c) A person with myopia can see nearby objects clearly. This is the reason; myopia is also known as nearsightedness.

Short Answer Questions

15. Draw ray diagrams each showing 

(i) Myopic eye and

Ans:

(ii) Hypermetropic eye

Ans:

16. A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw a ray diagram for the correction of this defect.

Ans: This student is unable to see far off objects. This means that the student is suffering from myopia. Doctor will prescribe a concave lens of suitable focal length.

17. How are we able to see nearby and also distant objects clearly? 

Ans: The human eye has the ability to accommodate. The eye muscles relax and the lens thins when we need to perceive distant objects. As a result, the focal length of the lens grows, allowing the eye to see farther away objects. When we need to view anything close by, the eye muscles tighten and the lens thickens. As a result, the focus length of the lens shortens, allowing the eye to perceive nearby things.

18. A person needs a lens of power –4.5 D for correction of her vision.

(a) What kind of defect in vision is she suffering from? 

Ans: Myopia

(b) What is the focal length of the corrective lens?

Ans: \[\frac{1}{f}\] or, $f = \frac{1}{p}$

= $\frac{1}{{ - 4.5D}}$

= $ - 0.22m$

(c) What is the nature of the corrective lens?

Ans: The negative sign shows that it is a concave lens.

19. How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Ans: As we proceed from top to bottom, the density of air layers rises. For this, one prism is placed near another prism so that one prism is in an erect position and another prism is in an inverted position. When a ray of white light enters the first prism, dispersion of light takes place. When coloured light passes through the second prism, it recombines to form a beam of white light.

20. Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also, indicate the order of the colours of the spectrum obtained.

Ans:

Order of colours from bottom to top: Violet, Indigo, Blue, Green, Yellow, Orange and Red.

21. Is the position of a star as seen by us its true position? Justify your answer.

Ans: Due to this, starlight bends towards the normal as it passes through different layers of the atmosphere. Due to this, the apparent position of the star is a little above its actual position in the sky.

22. Why do we see a rainbow in the sky only after rainfall? 

Ans: Formation of rainbow is only possible when dispersion of light takes place through a suitable surface. After rainfall, some raindrops remain in the clouds. Moreover, the opposite side of the sky works like a screen on which a rainbow is formed. Hence, a rainbow is seen in the sky only after rainfall.

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

Ans: Out of all the colours in the visible spectrum, blue colour scatters the most. Due to this, it is the blue colour which reaches our eyes. As a result, the colour of sky appears blue.

24. What is the difference in colours of the Sun observed during sunrise/sunset and noon? Give an explanation for each. 

Ans: At sunrise and sunset, the sky seems reddish, but at noon, it appears white. The sunlight has to travel a shorter distance to reach us at midday. The majority of the colours that reach us are dispersed. At noon, the sky appears white as a result of this. The least scattering colours are those near the red end of the spectrum. Sunlight must travel a greater distance to reach us during dusk and sunrise. Because red is the least distributed colour, it is able to approach us. As a result, the sky appears reddish during sunrise and sunset.

Long Answer Questions

25. Explain the structure and functioning of the Human eye. How are we able to see nearby as well as distant objects?

Ans: The human eye has following main parts:

Cornea: The human eye has a spherical shape. The interior of the eye is protected by a strong white covering. The cornea is the translucent front section of this covering.

Iris: Behind the cornea is a black muscular structure. The colour of the iris determines the unique colour of a person's eye.

Pupil: The pupil is the tiny opening in the iris. The iris regulates the size of the pupil and hence the amount of light that enters the eye. The pupil allows light to enter the eye.

Lens:The lens is constructed of translucent plastic and is thicker in the middle. The lens focuses light on the retina, which is located in the rear of the eye.

Retina: The retina is the rear of the eye. It functions similarly to a screen, on which an image is created. Photoreceptors in the retina of the eye, rods and cones, convert visible light into neural impulses that are delivered to the brain. This is referred to as transduction. The optic nerve is related to these nerve cells.

Formation of Image in Eye: Light rays enter the eye through the pupil and pass through the lens to reach the retina. Light rays are focused on the retina by a lens. On the retina, real, inverted, and smaller pictures are created. The message is sent to the brain via the optic nerve. Communication is decoded by the brain, and we experience vision.

26. When do we consider a person to be myopic or hypermetropia? Explain using diagrams how the defects associated with myopic and hypermetropic eyes can be corrected?

Ans: Myopia is a condition in which a person is unable to see distant objects well. Myopia is a condition in which a person's vision is blurred. When an image is produced in front of the retina, something occurs.

A person is deemed hypermetropic if he or she is unable to perceive a nearby item clearly. Hypermetropia is a condition in which a person's vision is blurred. When an image is produced behind the retina, this occurs.

Correction of Myopia: Myopia sufferers should use a concave lens with a proper focal length. The rays from infinity are diverged by the concave lens. The rays appear to be coming from the far point of this person's eye after refraction by the concave lens. As a result, a crisp image of a distant object is formed on that person's retina. With the aid of an appropriate concave lens, a myopic person is able to clearly see distant objects.

Correction of Hypermetropia: A convex lens with a proper focal length is required for a hypermetropic person. The light rays from a nearby object are converged by the convex lens. As a result, these light beams appear to be emanating from the person's eyes' close point. As a result, a crisp image of a nearby item is formed on that person's retina. With the aid of an appropriate convex lens, a hypermetropic person is able to clearly see close objects.

27. Explain the refraction of light through a triangular glass prism using a labelled ray diagram. Hence define the angle of deviation.

Ans: 

(i) ABC is prism with base BC

(ii) PE is an incident ray on surface AB. It makes ㄥPENwith the normal NE. This angle is the angle of incidence.

(iii) After entering the prism, the light ray bends towards normal. In this case, EF is a refracted ray. ㄥN'EF is angle of refraction.

(iv) Once the refracted ray emerges from the prism into air, it bends away from normal. In this figure, FS is an emergent ray. ㄥSFM is the angle of emergence.

Angle of Deviation: The angle between incident ray and emergent ray is called angle of deviation. Here, ㄥSGHis angle of deviation or ㄥD.

28. How can we explain the reddish appearance of the sun at sunrise or sunset? Why does it not appear red at noon? 

Ans: Colours near the red end of the spectrum scatter the least. This happens because of the short wavelength of reddish colours. During sunset and sunrise, sunlight needs to travel more distance to reach us. Red colour is able to reach us because it is scattered the least. Hence, the sky appears reddish during sunrise/sunset. 

The sky appears reddish during sunrise/sunset but it appears white at noon. During noon, the sunlight has to travel less distance to reach us. Most of the colours reaching us get scattered. Due to this, the sky appears white at noon.

29. Explain the phenomenon of dispersion of white light through a glass prism, using a suitable ray diagram.

Ans:

When a ray of light passes through a prism, it bends due to refraction. When the ray of light eventually emerges from the prism, it takes a radically different course than it did before. This is due to the prism's unusual shape.

The visible spectrum has varying speeds for different colours. As a result, different colours bend at various angles of departure. As a result, the emerging light appears as a band of seven colours, all of which are white light components. Violet, Indigo, Blue, Green, Yellow, Orange, and Red are the colours used.

Dispersion of light is the separation of white light into its various components.

30. How does refraction take place in the atmosphere? Why do stars twinkle but not the planets? 

Ans: There are various layers to the atmosphere. The upper layer is optically rare, but the bottom layer is optically denser. Refraction occurs as a result of this when light passes through different levels of the atmosphere. As light travels through the atmosphere, it bends towards the normal as it passes through thicker and denser layers. When compared to our planet, stars are a long way away. As a result, stars act as a point source of light. As a result, we can detect even the tiniest shift in their apparent position in the sky. As a result, the stars appear to twinkle. Planets, on the other hand, are rather close to Earth. As a result, they cannot be used as a light source. As a result, minor changes in their apparent position go unnoticed by us. Planets do not appear to twinkle as a result.

NCERT Exemplar Solutions for Class 10 Science Chapter 11 Human Eye and Colourful World contains brief answers to all the questions present in the NCERT Class 10 Exemplar textbook. All the NCERT Exemplar Solutions are designed in a proper manner according to the latest CBSE Class 10 Science Syllabus (2024-25) and NCERT Guidelines. Chapter 11 is all about the human eye and some other concepts like the power of accommodation, refraction of light through a prism, atmospheric refraction, etc. Students can learn some of the optical phenomena that occur in nature and also can know about the defects in vision and its correction, formation of the rainbow, splitting of white light and the reason behind the blue color of the sky.

About the Chapter

While Chapter 11 is tough to learn, the free Class 10 Science  NCERT Exemplar Solution for Chapter 11 provided here will help the students to get proper ideas about different kinds of questions in Chapter 11. These pdf solutions will help students to answer the questions quickly and students will be able to answer all the important questions asked in Chapter 11. 

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