Optics Question 621
Question: The plane surface of a plano-convex lens of focal length f is silvered. It will behave as
[MP PMT/PET 1998]
Options:
A) Plane mirror
B) Convex mirror of focal length 2 $ f $
C) Concave mirror of focal length $ f/2 $
D) None of the above
Show Answer
Answer:
Correct Answer: C
Solution:
Focal length of effective lens $ \frac{1}{F}=\frac{2}{f _{l}}+\frac{1}{f _{m}}=\frac{2}{f _{l}}+\frac{1}{\infty }\Rightarrow F=\frac{f _{l}}{2} $
