Optics Question 640
Question: If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power
[CBSE PMT 1996; AFMC 2002]
Options:
A) + 6.5D
B) - 6.5 D
C) + 7.5 D
D) - 0.75 D
Show Answer
Answer:
Correct Answer: D
Solution:
$ P=\frac{1}{F}=\frac{1}{f _{1}}+\frac{1}{f _{2}}=\frac{1}{(+0.8)}+\frac{1}{(-0.5)}=-0.75\ D $
