Question

Two lenses of power +5 D and -7 D are in contact with each other. Find out the power of the combination of the lenses. Combined lens will be convex or concave?

Answer 1

Given, P₁ = +5 D; P₂ = -7 D; P = ?
∴ The power of combination of the lenses
∴ P = P₁ + P₂
= +5 D – 7 D
or P = -2D
∵ As power is negative, so combination will be diverging or concave.