power 4dThe 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 -Optical power is also referred to as dioptric power, convergence power, refractive power, or refractive power. It is equal to P = 1 f. Dioptre Formula . The Dioptre formula is used to