Class 10 Science QnA by Anurag

Class 10 Science QnA by Anurag

Q1. Given below is a diagram showing a defect of human eye.

Study it and answer the following questions:

(1) Name the defect shown in figure.

(2) Give two possible reasons for this defect of eye in human being.

(3) Name the type of lens used to correct the eye defect.

(4) Draw a labelled diagram to show how the defect is rectified by using the lens.

Ans:
(1) Since the light rays from a nearby object are focused at a point behind the retina, the defect shown in the ray diagram is hypermetropia.

(2) This defect arises either because the focal length of the eye lens is too long or the eyeball has become too small.

(3) To correct this defect of vision, a convex lens is used, which has the ability to converge incoming rays for forming the image on the retina.

(4) Since a convex lens has the ability to converge incoming rays, it can be used to correct this defect of vision. The ray diagram for the corrective measure for a hypermetropic eye is shown in the given figure:

Q2. What do you mean by far point? What is the far point of adult human eye?

Q3. Name the defect of vision which result in the alteration of far points.

Q4. 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: For a myopic person concave lens is used to correct the problem.
Focal length = Distance of far point from eye
Hence, f = -80 cm = -0.8 m.
Power of lens = 1/f = 1/(-0.8) = -1.25 D

Class 10 Science QnA by Anurag

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