Optics Question 666
Question: If convex lens of focal length 80cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power
[AFMC 2002]
Options:
A) + 6.5 D
B) ? 6.5 D
C) + 7.5 D
D) ? 0.75 D
Show Answer
Answer:
Correct Answer: D
Solution:
$ \frac{1}{F}=\frac{1}{f _{1}}+\frac{1}{f _{2}}\Rightarrow \frac{1}{F}=\frac{1}{+80}+\frac{1}{-50} $
$ \Rightarrow $ $ F=-\frac{400}{3}\Rightarrow P=\frac{-3}{4}D $
