<P>A convex lens has 4 D POWER having a FOCALLENGTH + 0.25 m A convex lens has -4 D power having a focal length -0.25 m A concave lens has 4 D power having a focal length + 0.25 m A concave lens has -4 D power having a focal length + 0.25 m
Solution :Focal length of a convex lens is +ve (0.25 m) and so it power `P = (1)/(f) = + (1)/(0.25) = +4` D