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प्रश्न
A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain
(i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention
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उत्तर
Two possible reasons due to which this defect of vision may have arisen are
(a) increase in curvature of the lens
(b) increase in length of the eyeball
(i) A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of its retina as shown in the figure given below. In the given case student's far point is 5 m. So, image of the object placed beyond 5 m from his eyes is formed in front of the retina and hence appears blurred. That is why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) Since a concave lens has an ability to diverge incoming rays, it is used to correct this defect of vision. The image is allowed to form at the retina by using a concave lens of suitable power as shown in the given figure.
(b) Power of the required corrective lens (P) =`1/(f("in m"))`
`P =− 1/5 `
`P= −0.2 D`
Hence, the power of corrective lens is -0.2 D.
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संबंधित प्रश्न
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?
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Where is the near point of a person suffering from hypermetropia (or long-sightedness)?
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Observer the following diagram and answer the questions.
a) Which eye defect is shown in this diagram?
b) What are the possible reasons for this eye defect?
c) How this defect is corrected, write it in brief?
Name the following:
The photosensitive pigment present in the rod cells of the retina.
Name the common defects of the eye.
Give Technical Term:
The type of lens used to correct myopia is
Name the following:
Two kinds of accomodations.
