Question

Which mirror is used by a dentist to focus light on tooth of a patient
A. Concave mirror
B. Plane mirror
C. Convex mirror
D. Cylindrical mirror

Answer 1

- Hint: A mirror is used by a dentist to see the tooth of a patient by focusing the light rays on the patient’s tooth. 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.

Complete step-by-step solution -

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. This converging mirror is also known as 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 named F(focus). 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. Therefore, the correct answer is A. Concave Mirror.

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.

Note: This question can also be solved by cancelling other options because the other three mirrors convex mirror, plane mirror and cylindrical mirror cannot act as converging mirror. Thus, proving our one and only answer as a concave mirror.