The human eye is one of the most important organ of human body. It allows us to see objects around us. The human eye can easily distinguish around 10 million colours. Class 10 students have a chapter in their NCERT Science textbook, The Human Eye and Colourful World. Today in this article you can find out Class 10 Science NCERT Solutions for Chapter The Human Eye and Colourful World.
Question 1: What is meant by the power of accommodation of the eye?
Ans: When the ciliary muscles relax, the eye lens becomes thin so that far off objects are clearly visible to us. When we have to see nearby objects then the muscles contract and the eye lens become thick. This ability of the human eye to adjust the focal length accordingly is called as Power of accommodation. By doing this human eye is able to see both nearby and far off objects.
Question 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 the proper vision?
Ans: The person is suffering from myopia so he is able to see nearby objects clearly but not objects beyond 1.2 m. This is happening because the image is forming before the retina. so, we need a lens that diverges and forms the image on the retina. The concave lens will be used to treat his problem.
Question 3: What is the far point and near point of the human eye with normal vision?
Ans 3: The far point can be called as the maximum distance to which our eyes can see. Infinity is taken as a far point for our eyes.
Near point is the minimum distance from our eyes to which an object can be seen clearly. Objects which are less than this distance will not be visible clearly to us. 25 cm is taken as the near point for a human eye.
Question 4: 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?
The student can not see far off objects (blackboard) while he is sitting on the last bench. This problem is caused by myopia. A concave lens should be used to resolve this problem. By using a concave lens image will be formed on the retina and he will able to see the blackboard clearly.
Human Eye Class 10 NCERT Solutions Pg 197
Question 1: The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to:
(c) Near Sightedness
(b) The power of accommodation enables human eye to change the focal length of the eye lens according to the distance of different objects.
Question 2: The human eye forms the image of an object at its
(a) Cornea (b) Iris (c) Pupil (d) Retina
Ans: The image is formed on the retina of human eye
Question 3: The least distance of distinct vision for a young adult with normal vision is about:
(b) 2.5 cm
(c) 25 cm
(d) 2.5 m
Ans: The minimum distance to see any object clearly is 25 cm for the human eye. If the object is placed at a distance below 25 cm, it may not be visible to us clearly.
Question 4: The change in focal length of an eye lens is caused by the action of the
(c) Ciliary muscles
Ans. (c) Ciliary muscles enable the change in the focal length of the objects.
Question 5: 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 dioptres. What is the focal length of the lens required for correcting
(i) Distant vision
(ii) Near vision
Ans: Power = 1/f (focal length )
So, f= -0.181 m
For the near vision power = 1.5 D
f = 1/P
so, f= 1/1.5
= + 0.667 m
Question 6: 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?
Ans: The person is suffering from the diseases of myopia. The image will be formed in front of the retina. Hence, a concave lens will be used to resolve the problem.
Distance of object, u = infinity
distance of image, v = -80 cm
Focal length = f
Let us check the lens formula
1/v – 1/u= 1/f
-1/80 -1/infinity = 1/f
f = -80 cm i.e. -0.8m
Now let us find the power for f=-0.8m
Power, P= 1/f = -1.25 D
So, we will need a concave lens of power -1.25 D.
Question 7: Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1m. What is the power of the lens required to correct
Question 8: Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Ans: A normal eye is unable to see clearly the objects which are placed closer than 25 cm because the ciliary muscles can not contract easily for such a small distance. To see an object clearly it should be placed at a minimum distance of 25 cm. If we try to observe something placed at such a small distance it may be blurred.
Question 9: What happens to the image distance in the eye when we increase the distance of an object from the eye?
Ans 9: The image does not change even when the object’s distance from the eye is changed. This happens because the size of the eye can not be changed. The focal length of the eye lens can be changed and this helps the image to be formed at the right place, i.e is the retina of human eye.
Question 10: Why do stars twinkle?
Ans: Stars are at a very far off distance from the earth. Stars have the light of their own. When light from them enters the surface of the earth, refractions take place. This refraction at various stages cause the twinkling of stars. The air in the atmosphere has different densities at different points.
So, these were the solutions to NCERT Questions for Chapter The Human Eye and Colourful World. Stay tuned with careeradvice4u.com for Class 10 Science NCERT Solutions for other chapters.
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