Question

You have to see an erect image of a tall building using a mirror. Which type of mirror would you select? Draw an appropriate ray diagram to show the formation of the image of the building using the selected mirror.

Answer 1

Hint : To see an erect image of a tall building we would have to use a mirror with an outwards curvature, whose centre of curvature is away from the building. In a ray diagram, the two rays of light from the body will pass through the centre of curvature of the mirror without deviating and one ray will be parallel to the principal axis of the mirror.

Complete step by step answer
To see an erect image of a tall building using a mirror, we’d need a mirror that can form an erect image at any object distance greater than its focal length. This is the property of a convex lens which forms an erect image for different object distances from the mirror. The image will also have a smaller size than the object size which can enable us to see the full length of the building. The ray diagram of the system is as follows:

In the above diagram, $F$ is the focal length of the convex mirror and $C$ is its radius of curvature. A ray of light parallel to the principal axis of the lens will be reflected such that its extension passes through the focus of the mirror and another ray of light will be reflected completely in the opposite direction such that its extension passes through the centre of curvature of the mirror.

Note
The reason we cannot use a plane mirror is that we’d need a very large mirror size to view the building completely in the reflection. We’d require an even bigger concave mirror to view the building in the reflection and to get an erect image the building should be placed at a distance less than the focal length of the concave mirror which is impractical.