Optics Question 654
Question: A candle placed 25 cm from a lens, forms an image on a screen placed 75 cm on the other end of the lens. The focal length and type of the lens should be
[KCET 2000]
Options:
A) + 18.75 cm and convex lens
B) - 18.75 cm and concave lens
C) + 20.25 cm and convex lens
D) - 20.25 cm and concave lens
Show Answer
Answer:
Correct Answer: A
Solution:
$ u=-25cm,v=+75cm $
$ \Rightarrow $ $ \frac{1}{f}=\frac{1}{+75}-\frac{1}{-25}\Rightarrow f=+18.75 $ cm ; convex lens.
