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:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2
focal length (f) = -16 mm
object distance = -8 mm
∴ Using mirror formula,
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
$⇒\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{-16}-\frac{1}{-8}$
$=\frac{1}{16}$
$v=16mm$
$∴m=-\frac{v}{u}=\frac{-16}{-8}=2$