Optics problem: concave or convex

[cdotter]

Homework Statement

A dentist uses a curved mirror to view teeth on the upper side of the mouth. Suppose she wants an erect image with a magnification of 2.00 when the mirror is 1.25 cm from a tooth. (Treat this problem as though the object and image lie along a straight line.) What kind of mirror (concave or convex) is needed? Use a ray diagram to decide, without performing any calculations.

Homework Equations

The Attempt at a Solution

If object distance is less than focal length for a concave mirror, the image will be upright. But I'm not given focal length, so how am I supposed to know it's a concave mirror?

 

[kk727]

This is just testing your knowledge of mirrors, you do not really need any calculations or even any ray diagrams.

Just think about it; a convex mirror ALWAYS produces a virtual, erect, and reduced image. Since the dentist wants a magnified image, you already know that the mirror cannot be convex; hence it must be concave.

Within the focal point on concave mirrors, images are virtual and magnified, so that is what the dentist needs. Hope I helped!