Question

A thini, symmetric double convex lens of power P is cut into three parts A, B, and C as shown in Figure. The power of

A. A is P
B. A is 2P
C. B is `P//2`
D. C is `P//4`

Answer 1

Correct Answer - a.,c.
In case of part A, radii of the two surfaces will remain same. Hence, focal length of part A will be same as that of complete lens, i.e., power of part A will remain unchanged, i.e., power of A is P.
In case of part B, radius of one surface will remain same while that of other plane surface will be `oo` . Hence, focal length of part B will be double that of whole lens,i.e., power of part B is `P//2`