To obtain a virtual and magnified image of an object by using a concave mirror we should place the object between pole (P) and focus (F) on the principal axis.
The object should be placed at a distance less than 18 cm from the front of mirror.
Now, \(m=-\frac{v}{u}=+2\)
\(v=-2u\)
As, \(f=-18cm\)
Using mirror formula
\(\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\)
\(\frac{1}{-18}=\frac{1}{-2u}+\frac{1}{u}\)
\(\frac {1}{-18}=\frac{1}{2u}\)
\(u=-9cm\)
The object should be place at 9 cm in front of the mirror, which is between the pole and the focal point to obtain an image of magnification +2.
