A) 10 cm
B) 20 cm
C) 30 cm
D) 60 cm
Correct Answer: C
Solution :
From lens formula \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] ... (i) Also magnification \[(m)=\frac{v}{u}\] ... (ii) Given, \[f=20\,cm\], \[v=2\,\,u\] \[\therefore \] From Eqs. (i) and (ii), we get \[\frac{1}{20}=\frac{1}{2\,u}-\frac{1}{-u}\] \[\Rightarrow \] \[\frac{1}{20}=\frac{1}{2\,u}+\frac{1}{u}\]You need to login to perform this action.
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