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Name the eye defect in which eye lens becomes cloudy or milky. Mention the method for its correction. A person uses a lens of power -1.0 D for correcting his distant vision and for correcting his near vision he uses a lens of . power + 2.0 D. Calculate the focal length of the lenses required to correct these defects. Explain why a normal eye is not able to see clearly the objects placed closer than the near points. |
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Answer» (i) Sometimes, the crystalline lens of people at old age becomes milky and cloudy. This condition is called a cataract. This causes partial or complete loss of vision. It is possible to restore vision through a cataract sursery. (ii) Focal length for lens for distance vision =-1/1= -1 m Focal length for a lens for near vision = + 1/2 = +0.5 m (iii)The focal length of the eye lens, cannot be decreased below a certain minimum limit.If we try to read a printed page by, holding it very.close to our, eyes we may see the image being blurred or feel the strain in the eye. To see an object comfortably and distinctly we must hold it at about 25 cm from the eyes. |
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