Question

Mirror used by a dental surgeon is
A. Plane
B. Convex
C. Concave
D. Convex and concave

Answer 1

Hint: A mirror is used by a dental surgeon to see the teeth of a patient by focusing the light rays on the patient’s teeth. This will happen when the tooth of the patient is placed at the focus of the mirror which the doctor is using. For light rays to focus on a particular position, they should reflect through a converging mirror. For the tooth image to appear clearly, the image should be magnified. That means magnification should be greater than 1.

Complete step by step answer:
The mirror used by a dentist to focus light on a patient should be converging because the light rays coming from infinity undergo reflection by the mirror and finally converge at a certain point called focus of the mirror. The tooth of the patient will be placed at this focal point of the mirror. The mirror should also produce some magnification greater than 1. The mirror satisfying both the converging and magnifying properties is only a concave mirror. This reflection concept can be easily explained by the diagram below.

From the above figure, it is clear that the light rays coming from infinity are getting reflected and then after bending, all the rays converge at a point. For concave mirrors, magnification is greater than 1. Hence, the dentist can see a clear, magnified image of the tooth of the patient by using a concave mirror.

So, the correct answer is “Option C”.

Additional Information:
Magnification of a concave mirror is the ratio of the height of the image to the height of the object.
Magnification of a concave mirror formula is given by,
$$m\quad =\quad -\dfrac { v }{ u }$$ where, m refers to magnification
v refers to distance of the image from the mirror
u refers to distance of the object from the mirror
The negative sign means that the image is inverted.

Note:
This question can also be solved by cancelling other options because convex mirrors cannot act as converging mirrors and it is clear from the hint that a dental surgeon will surely require a converging and magnifying mirror. Thus proving our one and only answer as a concave mirror.