Question

a person who can see distinctly from a distance of 1m wants to read a book placed at a distance of 25cm . what kind of lens would he require? Calculate power of lens?
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Answer 1

Answer:

Explanation:

istance of the near point, x' = 100cm

power of the lens, P = ?

focal length of the lens, f = ?

So the focal length, f = x'×d / x'- d

= 100 ×25 / 100 - 25

= 100 × 25 / 75

f = 100 / 3 cm

So the power of a lens, P = 1/f(m)

= 100/100/3

or,. = 3/1

P = 3 D