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} $ .



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