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NCERT Solutions for Class 10th Science


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Chapter 11. Human Eye and Colourful World





Exercise : Chapter 11

Q1. The human eye can focus 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.

Answer: (b) accommodation.

Q2. The human eye forms the image of an object at its
(a) cornea. (b) iris (c) pupil. (d) retina.

Answer: (d) retina

Q3. The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m.

(b) 2.5 cm.

(c) 25 cm.

(d) 2.5 m.

Answer: (c) 25 cm

Q4. 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.

Answer: (c) ciliary muscles

Q5. A person needs a lens of power –5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?


Q6. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?


Q7. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.


Q8. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?


Q9. What happens to the image distance in the eye when we increase the distance of an object from the eye?


Q10. Why do stars twinkle?


Q11. Explain why the planets do not twinkle.


Q12. Why does the Sun appear reddish early in the morning?


Q13. Why does the sky appear dark instead of blue to an astronaut?



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