question_answer 5)

A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision, he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (a) distant vision, and (b) near vision?

Answer:

                For the near-sighted person, the power of the lens used for distant-viewing is -5.5 D.                 So,                                 For distance viewing                                 = -0.18 m = -18 cm                 Since the near-viewing section of the lens is corrected by + 1.5 D,             Focal length of near vision correction,