Calculate the focal length of a reading glass of a person, if the distance

Calculate the focal length of a reading glass of a person, if the distance of distinct vision is 75 cm

(a) 75.2 cm
(b) 25.6 cm
(c) 100.4 cm
(d) 37.5 cm

37.5 cm

Given: v = -75 cm and u = -25 cm

We know that, lens formula, we have 1/f = (1/v) – (1/u) ⇒ (1/f) = (-175) + (1/25) 1/f

= (1/25) – (1/75) = (3 – 1) / 75 = 2 / 75

Focal length of a glass, f = 75 / 2 = 37.5 cm

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