Optics Question 587
Question: A convex lens of focal length 84 cm is in contact with a concave lens of focal length 12 cm. The power of combination (in diopters) is
[MP PET 1991]
Options:
A) 25/24
B) 25/18
C) - 50/7
D) + 50/7
Show Answer
Answer:
Correct Answer: B
Solution:
Focal length of the combination $ \frac{1}{F}=\frac{1}{f _{1}}+\frac{1}{f _{2}} $
$ =\frac{1}{(+84)}+\frac{1}{(-12)} $
$ \Rightarrow F=-14\ cm $
$ \therefore P=\frac{100}{F}=\frac{100}{-14}=-\frac{50}{7}D $
