Question

A dentist uses a curved mirror to view the back side of teeth in the upper jaw. Suppose she wants an upright image with a magnification of 1.5 when the mirror is 1.9 cm from a tooth. Should she use a convex or a concave mirror? What focal length should it have?

Answer 1

She should use a concave mirror The reason is it can produce highly magnified images which is upright

Given magnification $M=1.5$

Object distance $u=1.9 \mathrm{~cm}$

$M=-\frac{v}{u}$

$\Rightarrow v=-m u=-1.5 \times 1.9=-2.85 \mathrm{~cm}$

From the mirror formula $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$

Substituting the values we get

$\frac{1}{f}=\frac{1}{1.9}-\frac{1}{2.85}$

$\Rightarrow f=5.7 \mathrm{~cm}$

Focal length of the mirror $f=5.7 \mathrm{~cm}$