Question

define one dioptre power of a lens. find the power of a concave lens of focal length 2m

Answer 1

A dioptre (British spelling) or diopter (American spelling) is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres. (1 dioptre = 1 m−1.) It is thus a unit of reciprocal length.

So,now

f=2
power = 1/2m

Answer 2

this also A correct answer thank you