Convex Mirrors

Convex spherical mirrors are made from a section of an outer silvered ball.

The image formed in a convex mirror is always erect, virtual and diminished in size.

Constructing a ray diagram for a convex mirror

A ray travelling parallel to the principal axis virtually emanates from the virtual focal point after reflection by the mirror. To draw the reflected ray you have to put your ruler on the principal focus on the far side of the mirror and the point where the ray hits the mirror. Draw a dashed line from the virtual focus point to the mirror edge and then a solid line for the reflected ray.

A ray that aims at the virtual centre of curvature of the mirror is reflected back along its own path. Put your ruler on the object point and at C (or 2F) on the far side of the mirror. Draw a dashed line from C to the mirror and then a solid line to represent the ray that gets reflected back along its own path.

A ray that aims at the virtual focal point as it goes towards the mirror will be reflected back along a path parallel to the principal axis Put your ruler on the object point and the far focal point. Draw a solid line to represent the incident ray from the object point to the mirror and then a dotted line to the focus. Now draw a reflected ray that goes from the point your incident ray hit the mirror parallel to the principal axis. Continue that with a dashed line on the far side of the mirror.

The point where these three dashed lines meet is the image point. See the examples below:

1. Obeject beyond C

2. Object between C and F

3. Object between F and V

4. Object at F

5. Object at C

Uses of Convex Mirrors

Convex traffic safety mirrors are designed to assist road safety and can help eliminate blind spots at corners, concealed entrances and exits, car parks and junctions.

Ceiling dome mirrors are Ideal for surveillance in shops, offices and industrial environments.They allow someone to watch what is going on in a wide area and allow shopkepers to spot theives and vandals.

Cab front rear-view mirrors can be used to prevent forklift truck accidents. The panoramic view significantly reduces blind spots at the rear of the vehicle. The driver can see at a glance, and without excessive movement any obstacles as he/she reverses

Portable inspection mirrors can be used for security and safety purposes. They are widely used by security firms and the miltary.

Historical Footnote

It has been said that Archimedes used a large array of mirrors to burn Roman ships during an attack on Syracuse . This has never been proved or disproved; however, recently, on a popular Discovery Channel show, MythBusters, a team tried to recreate the famous "Archimedes Death Ray". They were successful at starting a fire on a ship at 75 feet away, however, previous attempts to light the boat on fire using only the bronze mirrors available in Archimedes' time were unsuccessful, and the time taken to ignite the craft would have made its use impractical, resulting in the MythBusters team deciding that the myth was just a myth!