A) 10 cm
B) 30 cm
C) 20 cm
D) 60 cm
Correct Answer: B
Solution :
\[f\,\,-20cm,\,\,m=2\] As, \[m=\frac{-v}{-u}\] \[\therefore \,\,\,\,\,\,\,\,\,2=\frac{v}{u}\,\,\,\,\,\,\,or\,\,\,\,\,\,\,v=2\,u\] As, \[\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\] \[\therefore \,\,\,\,\,\,\,\,\,\,\,\frac{1}{u}+\frac{1}{2\,u}=\frac{1}{-20}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,u=-\,30\,cm\]You need to login to perform this action.
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