Question

A thin symmetric double convex lens of power P is cut into three parts A, B and C as shown then which of the following is correct?

• A. Power of A is P
• B. Power of B is P/2
• C. Power of C is P/2
• D. All of these

Answer 1

The correct option is D All of these

When the lens is cut horizontally there is no change in the focal length. Hence focal length and the power of part A are the same as the original lens i.e power of A is P.

When the lens is cut vertically its focal length doubles i.e part B and C has focal length 2f.
As we know P=1/f
Thus, power of B and C is P/2