Q17 of 25 Page 11

A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Find the nature, focal length and power of the lens, he requires for his spectacles. ( CBSE 2014)

Object distance, u = 25 cm

The distance of near point, d = 50 cm


Focal length, f = ??


Using the formula: f =


f = = = 50 cm


Power = = = 2D


As focal length is positive therefore he uses double convex lens.

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