Which of the following statements is true?

Options

A. A convex lens has 4 dioptre power having a focal length 0.25 m
B. A convex lens has - 4 dioptre power having a focal length 0.25 m
C. A concave lens has 4 dioptre power having a focal length 0.25 m
D. A concave lens has - 4 dioptre power having a focal length 0.25 m

Answer

A

Explanation

The power (P) of a lens of focal length (f) is given by P = 1/f where f is the focal length meter and power in dioptre.
Now,
P = 1/f
or, 4 = `1/f`
or `f=1/4`m = 0.25m.