• # question_answer A concave mirror of focal length 15 cm forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be A)            22.5 cm                                    B)            7.5 cm C)            30 cm                                       D)            45 cm

$f=-15\,cm,$ $m=+2$ (Positive because image is virtual)                    $\because \,m=-\frac{v}{u}\Rightarrow v=-2u$. By using mirror formula            $\frac{1}{-15}=\frac{1}{(-2u)}+\frac{1}{u}\Rightarrow u=-7.5\,cm$