A dentist has a small mirror of focal length 1.6 cm. He observes the cavity in the tooth of a patient by holding the mirror at a distance of 8 mm. from the cavity. The magnification is:

2

The correct answer is Option (3) → 2

focal length (f) = -16 mm

object distance = -8 mm

∴ Using mirror formula,

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

$⇒\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{-16}-\frac{1}{-8}$

$=\frac{1}{16}$

$v=16mm$

$∴m=-\frac{v}{u}=\frac{-16}{-8}=2$