Optics Question 675
Question: A magnifying glass is to be used at the fixed object distance of 1 inch. If it is to produce an erect image magnified 5 times its focal length should be
[MP PMT 1990]
Options:
A) 0.2 inch
B) 0.8 inch
C) 1.25 inch
D) 5 inch
Show Answer
Answer:
Correct Answer: C
Solution:
$ m=\frac{v}{u}=5\Rightarrow v=5 $ inch (Given u = 1 inch)
Using sign convention $ u=-\ 1\ inch,\ \ v=-\ 5\ inch $
$ \therefore \frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-5}-\frac{1}{-1}\Rightarrow f=1.25\ inch $
