UPSC NDA 2 2021 General Ability Solved Paper

(c) Power of a lens of focal length 25cm is +4 Dioptre.
First we will convert the focal length in meters.
⇒‌‌25cm=0.25m
Now, substituting the value of focal length in the formula of power of lens we
m−1 is also expressed as diopters or D
As it is a convex lens so its power is positive. Thus, the power of the lens is +4D.