Question Detail
Question
A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination in diopters is
Correct Answer
Option A is the correct answer.
Detailed Explanation
Power of a lens is P = 1/f (in meters). For convex lens, f₁ = 40 cm = 0.4 m, P₁ = 1/0.4 = +2.5 D. For concave lens, f₂ = -25 cm = -0.25 m, P₂ = -1/0.25 = -4 D. Total power P = P₁ + P₂ = 2.5 - 4 = -1.5 D.
Hint
The power of a combination of lenses in contact is the algebraic sum of their individual powers.