Optics Question 658
Question: An object has image thrice of its original size when kept at 8 cm and 16 cm from a convex lens. Focal length of the lens is
[UPSEAT 2001]
Options:
A) 8 cm
B) 16 cm
C) Between 8 cm and 16 cm
D) Less than 8 cm
Show Answer
Answer:
Correct Answer: C
Solution:
m = ± 3, using $ m=\frac{f}{f+u} $
For virtual image $ 3=\frac{f}{f-8} $ …..(i)
For real image $ -3=\frac{f}{f-16} $ …..(ii)
Solving (i) and (ii) we get $ f=12cm $
