Convex Mirror

Convex Mirror is a curved mirror where the reflective surface bulges out towards the light source. This bulging out surface reflect light outwards and are not used to focus light. These mirrors form a virtual image as the focal point (F) and the centre of curvature (2F) are imaginary points in the mirror that cannot be reached. This results in formation of images that cannot be projected on a screen as the image is inside the mirror. The image looks smaller than the object from the distance but gets larger as the object get closer to the mirror.

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In this diagram, the center of the original sphere is called as the center of the curvature (C) and the line that passes from the mirror’s surface through the sphere’s center is called as the principal axis. Mirror contains a focal point (F), located along the principal axis which is the midway between the center of curvature and mirror’s surface. Both the center of curvature and the focal point are located on the side of the mirror opposite the object. As the focal point is located behind the convex mirror, a mirror is said to have a negative focal length value.

Image Formation by Convex mirror

There are two possibilities with related to the position of the object in a convex mirror.

• When the object is at infinity
• When object is between infinity and pole

When Object is at infinity

When the object is at the infinity, a point sized image is formed at principal focus  i.e. behind the convex mirror. The image formed is highly diminished, virtual and erect.

When Object is between infinity and pole

When the object is between infinity and pole of a convex mirror, a diminished, virtual and erect image is formed between pole and focus i.e. behind the mirror. The image formed is diminished, virtual and erect.

Uses of Convex Mirror

• Convex mirrors are often used in the hallways of buildings including stores, schools, hospitals, hotels and apartment buildings.

• They are used in driveways, roads, and alleys to provide safety to all the bikers and motorists at curves and turns and other places where there is a lack of visibility.

• They are also used in some automated teller machines as a handy security feature that allow user to see what all is happening behind them.

• They are used in passenger side mirror on a car and somewhere it is labelled as “objects in mirror are closer than they appear” to warn the driver.