Question

A symmetric double convex lens is cut in two equal parts by a plane containing the principal axis. If the power of the original lens was 4 D, the power of a divided lens will be

(a) 2 D

(b) 3 D

(c) 4 D

(d) 5 D.

Answer 1

The correct answer is (c) 4 D

EXPLANATION: 

The plane containing the principal axis will cut the lens in two semicircular pieces and each piece will be a lens having the same radius of the curvatures. Hence each of the pieces will have the same focal length and the same power. Thus the option (c).