Question

Two lenses have powers +D and -2D respectively. The power of combination is:

• A. -D
• B. +D
• C. -2D
• D. +2D

Answer 1

The correct option is A -D

Given that the power of two lenses are $D$ and $-2D$.

Let the combined power be $x$.

We have $x=D-2D=-D$

Therefore option $A$ is correct.