Power `(P)` of a lens is given by reciprocal of focal length `(f)` of the lens.
Channel: Doubtnut
Date: 02/08/2020

Power `(P)` of a lens is given by reciprocal of focal length `(f)` of the lens. i.e. `P = 1//f`. When `f` is in metre, `P` is in dioptre. For a convex lens, power is positive and for a concave lens, power is negative. When a number of thin lenses of powers `p_(1), p_(2), p_(3)....`  are held in contact with one another, the power of the combination is given by algebraic sum of the powers of all the lenses   i.e., `P = p_(1) + p_(2) + p_(3) + ........`  Answer the following questions :   Focal length of the combined three lenses would be