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Q.
In order to obtain a real image of magnification 2 using a converging lens of focal length $20 cm ,$ where should an object be placed?
Ray Optics and Optical Instruments
Solution:
For real image $m=-v e$
$m=-2$
$\therefore $ As we know $M =\frac{ f }{ u + f }$
$-2=\frac{f}{u+f} $
$ \Rightarrow -2=\frac{20}{u+20}$
$ \Rightarrow -2 u+(-40)=20$
$u =-30 cm$