A dentist uses a mirror to obtain a large image of a patient’s tooth. Which mirror should the dentist use and why?

The correct option is: Concave mirror, because it gives a magnified image.

To understand why this is the correct choice, let us examine the properties of different types of mirrors and how they form images:

1. Plane Mirror: A plane mirror always forms a virtual, upright, and same-sized image (magnification is equal to 1). Since the dentist needs a large (magnified) image of the tooth to see details clearly, a plane mirror is not suitable.

2. Convex Mirror: A convex mirror always forms a virtual, upright, and diminished (smaller) image, regardless of the object's position. Therefore, it cannot be used to obtain a larger image of a tooth.

3. Concave Mirror: A concave mirror has the unique ability to produce a magnified (enlarged), upright, and virtual image when the object is placed close to the mirror, specifically between the mirror's pole (P) and its principal focus (F).

By placing the concave mirror very close to the patient's tooth, the tooth lies within the focal length of the mirror. This results in a magnified, erect, and virtual image of the tooth behind the mirror, allowing the dentist to examine it with high clarity.