Science
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Chapter 11: Human Eye and Colourful World
Class: X
Exercises 1
Question 1
What is meant by power of accommodation of the eye?
Answer 1
The eye lens becomes thin and the focal length increases, when the ciliary muscles are relaxed, and the distant objects become clearly visible to the eyes. The ciliary muscles contract making the eye lens thicker, and decrease in focal length of eye lens, so that nearby objects become clearly visible to the eyes. This ability of human eye to adjust the focal length of retina, for viewing both nearby and distant objects, is called the power of accommodation of the eyes.
Question 2
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be
the type of the corrective lens used to restore proper vision?
Answer 2
The person with myopic eye is able to see nearby objects clearly, but he is unable to see objects beyond 1.2 m, because the image of an object beyond 1.2 m is formed in front of
the retina and not at the retina, as the given figure shows.
That person should use a concave lens, to correct his vision defect. The concave lens will bring the image back to the retina as shown in the given figure.
Question 3
What is the far point and near point of the human eye with normal vision?
Answer 3
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 the normal human eye is infinity.
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?
Answer 4
A student has difficulty in reading the blackboard while sitting in the last row. It shows
that he is unable to see distant objects clearly. He is suffering from myopia. This defect
can be corrected by using a concave lens.
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