Question

Which mirror is used by a dentist to examine a small cavity?

• A. Plane mirror
• B. Convex mirror
• C. Spherical mirror
• D. Concave mirror

Hint:

Only a concave mirror can produce a magnified virtual image.
Therefore, it is used for shaving mirrors, makeup mirrors, and dentist mirrors.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks which type of optical mirror is utilized by dentists to inspect small cavities in a patient's teeth.

Step 2: Key Formula or Approach:
We need to identify a mirror that can form an enlarged (magnified), erect, and virtual image of a small object when placed close to it.

Step 3: Detailed Explanation:

• Let us evaluate the image characteristics of different mirrors:
1. Plane Mirror: Always forms a virtual, erect image of the same size as the object. It does not provide magnification.
2. Convex Mirror: Always forms a virtual, erect, but diminished (smaller) image. It is unsuitable for detail inspection.
3. Concave Mirror: Can form both real and virtual, inverted and erect, magnified and diminished images depending on the object's position.

• Specifically, when an object is placed very close to a concave mirror, i.e., between its principal focus (\(F\)) and pole (\(P\)), the mirror produces a virtual, erect, and highly magnified image of the object.

• Dentists hold a small concave mirror close to the tooth, positioning the tooth within its focal length. This produces a clear, enlarged image of the tooth, allowing them to inspect small cavities easily.


Step 4: Final Answer:
The mirror used by dentists is a concave mirror.