MP Board Class 10th Science imp questions Chapter 11 Human Eye and Colourful World

CHAPTER      11

The Human Eye and the Colourful World

 

Objective Questions

 

Multiple Choice Questions

 

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.

 

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

 

(a) cornea

 

(b) iris

 

(c) pupil

 

(d) retina.

 

(2019)

 

3 The leastdistance of distinct vision for a young adult with normal vision isabout:

 

 

(a) 25 m

 

(b) 2.5 cm

 

(c) 25 cm

 

(d) 2.5 m.

 

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.

 

5. What is the time difference between actual sunset and apparent sunset 7

 

(a) 2s

 

(b) 20s

 

(c) 2 min

 

(d) 20 min.

 

6. When light passes through a prism, the colour which deviates the least is

 

 

(a) red

 

(b) blue

 

(c) violet

 

(d) green

 

7. A person cannot see objects clearly beyond 50 cm. The power of lens tocorrect the vision is

 

(a) + 5 D

 

(b)-0-5 D

 

(c)-2 D

 

(d) + 2 D.

 

8. By which optical phenomenon the splitting of white light into seven Iconstituent colours occurs?

(a) Refraction

 

(b) Reflection

 

(e) Dispersion

 

(d) Interference

 

Ans. 1. (b), 2. (d), 3. (c), 4. (c), 5. (c), 6. (a), 7. (c), R. (c),

 

Fill in the Blanks

 

1. Scattering of light causes the …….colour of the sky.

 

2. To see objects with both eyes is called the… vision.

 

3……………. occur due to weakening of ciliary muscles in old age.

 

4. The point on retina at which optic nerve leaves the eye is called………….. At this point, if any image is formed is not sent to the……..

 

5. is the surface, which acts as screen and image is formed on it.

 

6. In the nearby objects are not distinctly visible.

 

7. For a young human adult with normal vision the far a point is at..……………..
8. The ………….colour is least scattered by fog or smog.

 

9. The least distance of distinct vision for young adult with normal vision is about………..

 

Ans. 1. blue, 2. binocular, 3. Presbyopia, 4. Blind spot, brain, 5. Retina,6. hypermetropia, 7. infinity, 8. red, 9. 25 cm.

 

True/False

 

1. Tyndall effect takes place due to scattering of light by the colloidal particles.

 

2. The sun is visible to us about 2 sec before the actual sunrise.

 

3. A rainbow is caused by diffraction of sunlight by water droplets in the atmosphere.

 

4. Isaac Newton was the first to use a glass prism to obtain the spectrum of sunlight.

 

5. In a bi-focal lens, the upper portion consists of concave lens and the lower is a convex lens.

 

6. The change in the curvature of eye lens cannot change its focal length. part

 

7. In a human eye, the iris controls the size of the pupil.

 

8. Myopia can corrected by ing a convex lens.

 

Ans. 1. True, 2. False, 3. False, 4. True, 5. True, 6. False, 7. True, 8. False. Match the Columns

 

Column ‘A’.                            Column ‘B’

 

 

1. Convex lens. (a) Far-sightedness

 

2. Concave lens (b) Facilitates near vision

 

3. Myopia. (c) Natural spectrum

 

4. Hypermetropia. (d) Facilitates distant vision

 

5. Rainbow. (e) Near-sightedness

 

6. Eye ball (f) 2-3 cm

 

 

Ans. 1. (b), 2. (d), 3. (e), 4. (a), S. (c). 6. → (1).

 

 

Answer in one Word/Sentence

 

1. In which type of eye defect far point of the eye gets reduced ?

Ans. In Myopia, the far point of the eye gets reduced.

 

2. Which type of lens should be used to correct presbiopia ?

Ans. Bi-focal lens.

 

3. What type of lens is used for correcting hypermetropia ?

Ans. Converging or convex lens.

 

4. Which component of the human eye controls the amount of light entering the eye ?

Ans. Pupil.

 

5. What is the least distance of distinct vision of a normal human eye ?

Ans. It is around 25 cm.

 

6. What would have been the colour of the sky if there was no atmosphere ?

Ans. It would be

 

7. Name the two phenomena involved in the formation of a rainbow.

Ans. Dispersion and total internal reflection are the two phenomena involved in the formation of a rainbow.

 

8. What is twinkling of stars due to ?

Ans. Due to refraction of light by the Earth’s atmosphere.

 

9. Where is the image formed in an eye suffering from long-sightedness?

Ans. The image is formed behind the retina.

 

10. Define dispersion of white light.

Ans. Splitting of white light into its various constituents is called dispersion of light.

 

Very Short Answer Type Questions

 

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

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

 

2. 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 ?

Ans. A person with a myopic eye should use a concave lens so as to restore proper vision.

 

3. 3. 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 ?

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

 

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

Ans. A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit.

 

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

Ans. 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.

 

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

Ans. 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 reaches the eyes of the astronaut and the sky appers dark to him.

 

7. 7. Why is the colour of the clear sky blue? Ans. The molecules of atmosphere and other particles present in the atmosphere scatter the blue colours of light at maximum extant, that scattered blue colour falls in our eyes due to which the colour of the clear sky appears blue.

 

Short Answer Type Questions

 

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

Ans. 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 a normal human eye is infinity.

 

2. 2. Why do stars twinkle ?

Ans. Stars twinkle due to atmospheric refraction of the light from the stars. As the stars are very far away, they behave as almost point sources of light. Due to atmospheric refraction, the path of light rays coming from the star goes on varying, the apparent position of the star fluctuates and the amount of light from the star entering the eye flickers. So, sometimes, the star appears brighter, and sometimes fainter. Thus, the stars twinkle.

 

 

Q 3. Explain why the planets do not twinkle. Ans. Planets are much closer to the earth and are seen as extended sources. So, a planet may be considered as a collection of a large number of point-sized light sources. Although light coming from individualized point-sized sources flickers, but the total amount of light entering our eyes from all the individual point-sized sources average out to be constant. Thus, planets appear equally bright and there is no twinkling of planets.

 

4. 4. Why does the sun appears reddish early in the morning ?

Ans. During sunrise, the light rays coming from the sun have to travel a greater distance in the earth’s atmosphere before shorter wavelengths of light are scattered 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.

 

At noon, the sun is overhead, so the distance. Hence, there is only slight scattering of shorter wavelengths of blue and violet colour. Therefore, the sun appears white.

 

5. 5. Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles in old age. What type of lenses are required by the persons a suffering from this defect, to see the objects clearly?

Ans. The curvature of the eye lens can be adjusted by the ciliary muscles. This changes the focal length of the lens. The defect which arises due to the gradual weakening of the ciliary muscles is known as presbyopia. A bifocal lens is used to correct this defect

 

6. 6. Draw a diagram of dispersion of white light by the glass prism.

Ans –

7. 7. What do you mean by dispersal of light? Draw a labelled diagram of dispersion of white light by the glass prism.

Ans. The phenomenon of splitting of white light into a band of several colours when

it passes through a prism, is called dispersion of light. Diagram of dispersion of white light by the glass prism See fig. 11.2.

 

8. 8. Draw a well labelled diagram of human Ans.

9. 9. Draw a labelled diagram of refraction of light through a prism.

Ans. Refraction of light through a prism:

10. 10. Draw a ray diagram of scattering of light in colloidal solution.

Ans. Scattering of light in a colloidal solution :