An object is placed at a distance of 10 cm from a concave mirror of focal length 15 cm. The magnification of the image is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 3
Given:
Object distance: $u = -10\ \text{cm}$ (concave mirror, object in front)
Focal length: $f = -15\ \text{cm}$ (concave mirror)
Mirror formula: $\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \Rightarrow \frac{1}{v} = \frac{1}{f} - \frac{1}{u}$
$\frac{1}{v} = \frac{1}{-15} - \frac{1}{-10} = -\frac{1}{15} + \frac{1}{10} = \frac{1}{30}$
$v = 30\ \text{cm}$
Magnification: $m = -\frac{v}{u} = -\frac{30}{-10} = 3$
∴ Magnification of the image = 3