power 4dTo find the effective power of a combination of a convex lens and a concave lens, we can follow these steps: 1. Identify the Powers of the Lenses : - The power of the convex lens (P1) is givenThe focal length of a lens with a power of +4D is 25 cm. Show More | Share Save. Class 12 PHYSICS GEOMETRICAL OPTICS. Topper's Solved these Questions. OPTICS BOOK -