Question

A symmetrical double convex lens is cut into two equal parts along a plane perpendicular to the principal axis . if the power of the original lens is 4D then the power of one of the two pieces is D

Answer 1

It will become two lenses of +2D each.

So the strength of each part is halved. This means the focal length of each half will be double that of the original lens:

4Dharrf=0.25m and 2Dharrf=0.50m