A) 30 cm
B) 60 cm
C) 15 cm
D) 90 cm
Correct Answer: D
Solution :
The image formation by a convex lens is as follows: Image formed is diminished, when object lies between 2F and infinity. Magnification \[(M)=\frac{image\,size}{object\text{ }size}\] \[=\frac{1}{2}=\frac{v}{u}\] ??? (i) From lens formula, \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] ???.. (ii) where \[f\]is focal length, v the image distance and u the object distance. From Eqs. (i) and (ii), we get \[\frac{1}{f}=\frac{1}{u}+\frac{2}{u}\] Given, \[u=90\text{ }cm\] \[\therefore \] \[\frac{1}{30}=\frac{3}{u}\] \[\Rightarrow \] \[u=90\text{ }cm\]You need to login to perform this action.
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