Optics Question 915
Question: The relation between the linear magnification $ m, $ the object distance $ u $ and the focal length $ f $ is
Options:
A) $ m=\frac{f-u}{f} $
B) $ m=\frac{f}{f-u} $
C) $ m=\frac{f+u}{f} $
D) $ m=\frac{f}{f+u} $
Show Answer
Answer:
Correct Answer: B
Solution:
$ \because m=-\frac{v}{u} $ also $ \frac{1}{f}=\frac{1}{v}+\frac{1}{u} $
Therefore $ \frac{u}{f}=\frac{u}{v}+1 $
Therefore $ -\frac{u}{v}=1-\frac{u}{f} $
$ \Rightarrow \frac{-v}{u}=\frac{f}{f-u} $ so $ m=\frac{f}{f-u} $ .
