Q16 of 70 Page 11

When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored?

Cataract develops when the eye-lens of a person becomes unclear due to the formation of a membrane over it. The vision of a person having cataract can be restored after getting cataract surgery done on the eye-lens having cataract. This defect cannot be corrected by any type of spectacle lenses.

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14 How do we see colours? 15 How does an eye focus the objects lying at various distances? 17 Where should an object be placed in front of a convex lens so as to use it as a simple microscope? 18 If we need magnification of 375 from a microscope of tube length 15 cm and objective of focal length 0.5 cm, what focal length of eye-piece should we use?