Optics Question 815
Question: Convex surface of thin concavo-convex lens of refractive index 1.5 is silvered as shown. A small object is kept in air at 30 cm left of the lens on its principal axis. The distance of the final image is
Options:
A) 20cm
B) 30cm
C) 10cm
D) 15cm
Show Answer
Answer:
Correct Answer: C
Solution:
[c] Power of combinations $ P=2( \mu -1 )( \frac{1}{-60}-\frac{1}{-20} )+( \frac{-1}{-20/2} ) $
$ P=\frac{2}{15}=\frac{-1}{f} $
$ \therefore $ Resultant focal length $ f=-\frac{15}{2} $
$ \therefore $ From mirror formula $ \frac{1}{-30}+\frac{1}{v}=\frac{1}{f} $ Solving $ v=-10cm. $
