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 in metre and power in dioptre.
`P=(1)/(f)` or `f=(1)/(P)=(1)/(4)=0.25 m`