A) \[-5\text{ }cm\]
B) +5 cm
C) +7.5cm
D) \[-7.5\text{ }cm\]
Correct Answer: A
Solution :
Magnification is ratio of size of image to that of object Here, \[\mu =-1.5f\] \[f=-f\] From concave mirror formula \[\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\] we have, \[\frac{1}{(-f)}=\frac{1}{v}+\frac{1}{(-1.5f)}\] \[=\frac{1}{v}=\frac{1}{-3f}\] or \[v=-3f\] Now, magnification in mirror is given by \[m=\frac{I}{O}=-\frac{v}{u}\] where,\[I\]is size of image and\[O\]is size of object. Here, \[O=+2.5\text{ }cm\] \[\frac{I}{2.5}=\frac{-3f}{-(-1.5f)}\] \[I=-5\,cm\]
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