Optics Question 586
Question: A thin convex lens of focal length 10 cm is placed in contact with a concave lens of same material and of same focal length. The focal length of combination will be
[CPMT 1972; 1988]
Options:
A) Zero
B) Infinity
C) 10 cm
D) 20 cm
Show Answer
Answer:
Correct Answer: B
Solution:
$ f=\frac{f _{1}f _{2}}{f _{1}+f _{2}}=\frac{10(-10)}{10+(-10)}=\frac{-100}{10-10}= $ $ \infty $
