Question

The mirror used in a dressing table is a –
A. Concave mirror
B. Convex mirror
C. Plane mirror
D. None of these

Answer 1

Hint: The mirror used in a dressing table must form a virtual and erect image. Also, the image should be of the same size as the object. Recall the properties of the spherical mirrors and plane mirror to answer this question.

Complete answer:
When we see our image in the mirror of a dressing table, the image appears inside the mirror and therefore we can say that the image is virtual. Also, the image should be erect so we can see the proper image of ourselves. The magnification of the mirror should be equal to 1 so as the image of the object remains equal to the size of the object irrespective of the distance of the object from the mirror.

Now, let us check the characteristics of the image formed by the mirrors given in the options.We know that a concave mirror forms both a real image and a virtual image of the object depending on the position of the object from the mirror. The height of the image depends on the position of the object from the concave mirror. The focal length of the concave mirror is never equal to 1. Therefore, the image distance and object distance are not equal. Thus, we cannot select a concave mirror for the mirror of the dressing table.

We know that convex mirrors always form virtual, erect and diminished images. But the magnification of the convex mirror never equals to 1 and therefore the height of the image and height of the object varies. Therefore, we cannot select a convex mirror for the mirror of the dressing table.

We know that the plane mirror has an infinite focal length. Therefore, the distance of the image is equal to the distance of the object from the mirror. Also, the image formed by the plane mirror is always virtual, erect and of the same size as the object. Therefore, the mirror used in the dressing table is always the plane mirror.

So, the correct answer is option C.

Note:To answer these types of questions, students must remember all the properties of spherical mirrors. Students must be able to determine the nature of the image by memorizing the ray diagram of the image formation. When the image forms behind the mirror, the image is always virtual.