Study Important Questions for Class 10 Science Chapter 10 - Human Eye and Colourful World

 

Study Important Questions for Class 10 Science Chapter 10 - Human Eye and Colourful World

Very Short Answer Questions (1 Mark)

1. When a person is myopic, he/ she can clearly see

1. Both nearby and far-off objects

2. Only nearby objects

3. Only far-off objects

4. Neither near nor far off objects

Ans: b. Only nearby objects

2. The defect of myopia can be corrected by using

1. Concave lens

2. Convex lens

3. Either concave or convex

4. A complicated combination of lenses.

Ans: a. Concave lens

3. The colour that is scattered the least by the tiny particles and the atoms/ molecules of the atmosphere is

1. Violet

2.  Green

3.  Yellow

4.  Red

Ans. d. Red

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

1. Dispersion of light

2. Scattering of light

3. Total internal Reflection

4. Reflection of light from the earth

Ans: b. Scattering of light

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

1. are relaxed and lens becomes thinner

2. contract and lens becomes thicker

3. are relaxed and lens becomes thicker

4. Contract and lens become thinner.

Ans: a. are relaxed and lens becomes thinner

6. Define the power of accommodation?

Ans: The power of the eye lens to focus on objects near or far from the retina by adjusting its focal length is called the power of accommodation.

7. Which part of the human eye provides most of the refraction for the light rays entering the eye?

Ans: Cornea and Aqueous humour provides most of the refraction for the light rays entering the eye.

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

Ans: When the distance of an object from the eye is increased, the image distance remains the same and the image is formed on the retina of the eye.

9. What happens to the pupil of the eye when the light is very bright?

Ans: When the light is very bright, the pupil’s size becomes smaller and limits the extent of light entering the eye.

10. Which part of the human eye conveys the electrical signals generated by the light sensitive cells of the retina to the brain?

Ans: Optic nerves convey the electrical signals generated by the light sensitive cells of the retina to the brain.

11. The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to

1. Presbyopia

2. Accommodation

3. Near-sightedness

4. Far-sightedness

Ans: b. Accommodation

12. What would have been the colour of the sky if there had not been any atmosphere around the earth?

Ans: The colour of the sky would be black if there had not been any atmosphere around the earth.

13. For dispersion of light through a prism which colour has a maximum deviation?

Ans: Violet has the maximum deviation for dispersion of light through a prism. 

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

Ans: The least distance of distinct vision of a normal human eye is 25 cm.

15. Name the muscle responsible for bringing change in the focal length of the eye lens?

Ans: Ciliary muscles are responsible for bringing change in the focal length of the eye lens. 

16 Name one defect of vision which cannot be corrected by any type of spectacle lens?

Ans: Cataract, clouding of the lens of the eyes is a vision defect that cannot be corrected by any type of spectacle lens.

17. State one effect produced by the scattering of light by the atmosphere?

Ans: Tyndall effect is produced by the scattering of light by the atmosphere.

18. What is the nature of the image formed on the retina of the eye?

Ans: The image formed on the retina of the eye is real and inverted.

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

Ans: Convex lens is used to rectify hypermetropia or long-sightedness.

20 Who was the first person to obtain the spectrum of sunlight?

Ans: Sir Isaac Newton was the first person to obtain the spectrum of sunlight.

21 Why does the Sun appear reddish early in the morning?

Ans: During sunrise, the sun is at the farthest distance from the earth’s surface. The light rays travel a large distance in the Earth’s atmosphere before reaching our eyes. 

While passing through the atmosphere, the light rays with shorter wavelengths get scattered by the Earth’s atmosphere and the red-colored light with the longest wavelength is able to reach our eyes. Hence, the Sun appears reddish early in the morning. 

22. A person wears eyeglasses of focal length 70 cm. What is the far point of the person?

23 Why do we observe random wavering or flicking of the objects near a fire or on a very hot day?

Ans: We observe random wavering or flicking of the objects near a fire or on a very hot day because of atmospheric refraction. The area above the fire is hot and is lighter than the cool air above it due to which its refractive index is low and density also does not remain the same. Therefore, the apparent position of the object flickers.

24. Why are we not able to see things clearly when we come out of a dark room?

Ans: In a dark room, the iris expands the pupil which allows more light to enter the eye. As we come out of the darkroom, a large amount of light enters our eyes and because of the glare, we are not able to see things clearly.

Short Answer Questions (3 Marks)

1. Explain in brief:

a. What is hypermetropia?

Ans: Hypermetropia (long-sightedness) is a vision defect where nearby objects appear blurred but the distant objects can be seen clearly.

b. What are the two causes of this defect of vision?

Ans: The two possible causes of this defect are:

(i). An increase is the focal length of the eye lens or the power of the eye lens decreases 

(ii). Size of the eyeball decreases

2. Explain the scattering of light?

Ans: Scattering of light is defined as the change in the direction of light on striking an obstacle such as dust, water vapour, etc.

3.What is presbyopia? State the causes of this defect? How is the presbyopia of a person corrected?

5. The rainbow is a natural spectrum appearing in the sky after a rain shower.

a. Is it correct to say that a rainbow is always formed in a direction opposite to the sun?

Ans: Yes, a rainbow is always formed in a direction opposite to the sun as a rainbow is just the sunlight that has been refracted and reflected.

b. Can it be seen on a sunny day?

Ans: Yes, a rainbow can be seen on a sunny day if the Sun’s beam passing through the droplets of water suspended in the atmosphere, reaches the observer’s eye.

c. Arrange the sequence in correct sequential order Refraction, Internal Reflection, Refraction & Dispersion.

Ans: The correct sequential order is:

Refraction & Dispersion, Internal Reflection, Refraction.

6. A reporter records the following observations of an astronaut from his spaceship. Justify each statement.

a. The length of the day is the same as observed on the earth.

Ans: This statement is not true as the length of the day in space can be four minutes shorter than on Earth.

b. Space appears black in colour.

Ans: The statement is correct because in space there is no atmosphere. Hence, there is no scattering of light.

c. The star appears to twinkle while the planets do not do so as they do on the earth.

Ans: The statement is incorrect since we know that the twinkling of stars is due to atmospheric refraction and space has no atmosphere. Hence, the stars do not appear to twinkle in space.

7. Why do stars twinkle?

Ans: Twinkling of stars is due to the atmospheric refraction of light. Stars behave as point sources of light since they are present far away. The path of the light rays from the star experiences atmospheric refraction and the position of the star appear to change. Also, the amount of light entering the eye flickers, so sometimes the star appears brighter and at other times fainter. Thus, the stars twinkle.