A) 36 cm
B) 27 cm
C) 60 cm
D) 30 cm
Correct Answer: D
Solution :
if side of object square \[=\ell \] and side of image square \[=\ell '\] From question, \[\frac{{{\ell }^{,2}}}{\ell }=9\] or \[\frac{\ell '}{\ell }=3\] i.e., magnification \[m=3\] \[u=-40\,cm\] \[v=3\times 40=120\,cm\] \[f=?\] From formula, \[\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\] \[\frac{1}{120}-\frac{1}{-40}=\frac{1}{f}\] or , \[\frac{1}{f}=\frac{1}{120}+\frac{1}{40}=\frac{1+3}{120}\]\[\therefore \]\[f=30\,cm\]You need to login to perform this action.
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