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