Optics Question 645
Question: A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a
[SCRA 1998]
Options:
A) Convex mirror of focal length 10 cm
B) Concave mirror of focal length 40 cm
C) Concave mirror of focal length 60 cm
D) Concave mirror of focal length 10 cm
Show Answer
Answer:
Correct Answer: A
Solution:
$ \frac{1}{F}=\frac{2}{f}+\frac{1}{f _{m}} $ . Here $ f _{m}=\infty $ , hence $ F=\frac{f}{2}=10cm $
