Question

find the focal length ( in cm ) of a lens of pwer 2D identify the type of this lens

Answer 1

as the power is the inverse of focal length so the focal length of the above lens will be 0.5m or 50 cm
as the power is positive therefore it is a converging lens

Answer 2

As power is inversely propetional to focal lenth
so
Power=1/focal lenth
2=1/focal length
focal lenth=1/2
focal lenth=0.5m
focal lenth=0.5*100 cm
focal lenth=50 cm
it is convex lens