If the power of a glass lens is +2 diopters, its focal length will be :

Correct answer: (c) 50 cm

Explanation

The power of a lens is P = 1/f, with f in metres; it is measured in dioptres.

For P = +2 D: f = 1/2 m = 0.5 m = 50 cm. The positive sign shows a convex (converging) lens.