Question

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

Answer 1

The correct option is B 7.5 cm

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

$\frac{1}{-15}=\frac{1}{(-2u)}+\frac{1}{u}\Rightarrow u=-7.5cm$