Answer to Question #2857 in Optics for tom

Question

A dentist uses a small mirror of radius 40 mm to locate a cavity in a patient's tooth. If the mirror is concave and is held 16 mm from the tooth, what is the magnification of the resulting image?

Answer 1

The focal length of the mirror is f = R/2 = 20 mm.
The distance of the image could be calculated be the formula:
1/f = 1/d0 + 1/d1
Thus
-1/20 = -1/16 + 1/d₁
d₁ = 80 mm.
The magnification is m = -d1/d0 = 80/(-16) = 5