# NCERT Exemplar Class 10 Science Chapter 11 The Human Eye and the Colourful World Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 11 The Human Eye and The Colourful World covers all the important questions and answers as well as advanced level questions. It helps in learning about the Light, Normal rays, Incident rays, Reflected rays, Angle of incidence, angle of reflection, point of incidence and Laws of reflection.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 11 The Human Eye and The Colourful World is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like Laws of refraction, characteristics of an image formed by the plane mirror, mirror formula, spherical mirrors and its types, lens, power of lens real image and inverted image. .

 Chapter Name Chapter 11 The Human Eye and The Colourful World Book Title NCERT Exemplar for Class 10 Science Related Study NCERT Solutions for Class 10 Science Chapter 11 The Human Eye and The Colourful WorldRevision Notes for Class 10 Science Chapter 11 The Human Eye and The Colourful WorldMCQ for Class 10 Science Chapter 11 The Human Eye and The Colourful WorldImportant Questions for Class 10 Science Chapter 11 The Human Eye and The Colourful World Topics Covered MCQShort Answers QuestionsLong Answers Questions

### Multiple Choice Questions

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

Solution
(b) -0.5 D

The person is myopic and hence he needs a concave lens. The power will be in negative.
P = 1/f = 1/2m = 0.5 D

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 text book. 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

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

In hypermetropia, the near point of eye move away from25 cm.

3.  A prism ABC (with BC as 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? The Human Eye and the Colourful World CHAPTER11 Fig.11.1

(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)

Solution
(b) (ii)

If the prism is kept with BC as the base, then the emergent band of colour will be violet at the bottom. If prism is kept with BC at the top, then violet would be 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) blue colour is scattered the most
(d) red colour is scattered the most

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

This is due to dispersion of light by the atmosphere.

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

Solution
(c) Refraction, dispersion and internal reflection

Dispersion is the scattering of white light into different color. Refraction bends incident light leading to the formation of rainbow.

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

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

The apparent position of the star keeps changing because of refraction of light by different layers of the atmosphere which have varying optical densities.

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

Solution
(c) violet and blue lights 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 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

Solution
(c) All the colours of the white light move with 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

Solution
(b) is scattered the least by smoke or fog

Red light can be seen form a larger distance as its wavelength is the largest. Also, it is the color which is least scattered by the smoke or smog.

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

Solution
(b) Scattering of light

Red color scatters the least. During sunset or sunrise light travels a longer distance to reach the earth. Hence the light from the sun will be red as it reaches the earth.

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 water
(c) scattering of light
(d) absorption of light by the sea

Solution
(b) reflection of sky in water

Water is colorless. Water reflects the blue colour of the sky.

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

Solution
(b) outer surface of the cornea

Cornea is a thin membrane through which light is entered. The incident light rays are bent due to cornea and are converged which results in image formation at retina. So, most of the refraction occurs at the iris of the eye.

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

Solution
(a) are relaxed and lens becomes thinner

14. Which of the following statement 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

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

Myopia is a condition in which a person cannot see distant objects clears but he can see nearer objects clearly.

Hypermetropia is a condition where a person cannot see the nearer object clearly but he can see the distant objects clearly.

15. Draw ray diagrams each showing
(i) myopic eye and
(ii) hypermetropic eye.

Solution

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 ray diagram for the correction of this defect.

Solution

The student is suffering from myopia (nearsightedness). Doctor advises her to use a concave lens of appropriate power to correct this defect.

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

Solution

Our eyes can change the focal length of the lens and hence it can focus on the images from varied distance. Ciliary muscles help in changing the focal length of the lens.

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

Solution

(a) The person issuffering from myopia.

(c) 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.

Solution

When two identical prism are placed in inverted position with respect to the other, we see that an arrow beam of white light incident on one prism emerges out of the second prism as 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.

Solution

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

Solution

The light form the star undergoes continuous refraction on entering the earth’s atmosphere. Refraction occurs in a medium of gradually changing refractive index. The apparent position of the star is slightly different from its actual position because the light form the star is bend towards the normal as it travels through the atmosphere. The star appears slightly higher than its actual position.

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

Dispersion of sunlight by tiny water droplets present in the atmosphere lead to the formation of rainbow. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets in the atmosphere act like tiny prisms thereby refracting and dispersing the incident sunlight. Then the light is finally reflected internally and refracted again as it comes out of the raindrop.

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

Solution

Blue colour in the white light suffers maximum scattering. This is the reason why makes the sky appears blue.

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

Solution

The sun is closer to the horizon during sunrise and sunset. As a result, the light from the sun passes through denser layer of air and covers a larger distance before reaching our eyes. The blue light is mostly scattered and the red color reaches us. This gives the red appearance to the sun at sunrise and sunset. The light form the sun travels lesser distance during the noon. Most of the colors get scattered and this is the reason why sun appears white in color.

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

Solution

The parts of the human eye are:

1. Cornea –The light enters the eye through a thin membrane called the cornea. It is the transparent bulge in the front surface of the eyeball. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.
2. Iris- It is a dark muscular diaphragm. The colour of the iris is responsible for the unique colour of a person’s eye.
3. Pupil –It is a small opening in the iris and thus it regulates and controls the amount of light entering the eye.
4. Lens -It is made up of  a transparent material and is thicker at the middle. The eye lens forms an inverted real image of the object on the retina.
5. Retina -The retina is a delicate membrane having enormous number of light-sensitive cells. The light-sensitive cells generate electrical signals upon illumination. These signals are then sent to the brain via the optic nerves. The brain interprets these signals, and finally, processes the information so that we perceive objects as they are.

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

Solution

A myopic person cannot see the distant objects clearly. In case of myopia the image is formed in front of retina. Hypermetropia is a condition where a person cannot see the nearer objects clearly. In case of hypermetropia the image is formed behind the retina.

Correction of Myopia

A concave lens of suitable power can be used for the correction of myopia. The lens will bring the image back on to the retina.

Correction of Hypermetropia
Convex lens of suitable power can be used for the correction of hypermetropia. Convex lenses provide additional focusing power which is required for bringing the image back on the retina.

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

Solution

The phenomenon of refraction through a triangular glass prism is shown in figure below.

At the surface AB, a ray of light PE enters the glass from air. This ray bends towards the normal and is represented as EF. At the surface AC, the light ray is travelling from glass to air and hence it bents away from normal. The angle between the incident ray and the emergent ray is called angle of deviation.

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

Solution

The sun is closer to the horizon during sunrise and sunset. As a result, the light from the sun passes through denser layer of air and covers a larger distance before reaching our eyes. The blue light is mostly scattered and the red color reaches us. This gives the red appearance to the sun at sunrise and sunset. The light form the sun travels lesser distance during the noon. Most of the colors get scattered and this is the reason why sun appears white in color during noon.

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

Solution

A ray of light bends on entering a prism because of the phenomena of refraction. The emergent ray is deviated from the original path. The various colours in the visible spectrum travel with different speeds. Because of this, the angle of deviation is different for different colours. As a result, the emergent light appears as a band of seven colours which constitute white light. These seven colours in the spectrum are violet. indigo, blue, green, yellow, orange and red. Splitting of white light into its different components is called dispersion of light.

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

Solution
As the height changes, the optical densities of air particles also change. The air layer near the surface is optically denser and that away from the surface are optically rarer. Because of this, as light travels through the atmosphere, refraction takes place. The ray of light bends towards the normal as it travels from a rarer medium to a denser medium. Stars are farther from us as compared to the planets. This is the reason why stars serve as a point source of light. The stars appear to twinkle because even a slightest change in their apparent position is clearly perceived.

Planets are nearer and hence they do not serve as point sources of light. Therefore, a minor change in their apparent position is not perceived. This is the reason why planets do not twinkle.