Properties of spherical mirrors

The chrome-plated soup ladle serves as an example of a concave and convex spherical mirror

In general, like plane mirrors, spherical mirrors are also present in our daily lives. They are found in several places, such as inside public transport buses, in elevators, in stores, etc. Although spherical mirrors, as well as planes, reflect the image, this reflection is not entirely perfect, that is, the reflection is not normal, and the images are slightly distorted.

We defined, in a previous moment, that a spherical mirror is nothing more than a reflecting surface in the form of a spherical cap. Thus, when the reflecting surface is internal, the mirror is called concave; and when the reflecting surface is external, the mirror is said to be convex. Let’s look at some properties of the spherical mirror.

1 – Incident ray parallel to the main axis

When the incident ray arrives at the spherical mirror parallel to the principal axis, it is reflected in the direction of the principal focus of the spherical mirror.

2 – Incident ray in the direction of the focus

When the incident ray arrives at the spherical mirror in the direction of the principal focus, it is reflected parallel to the principal axis.

3 – Radius incident towards the center of curvature

When the incident ray reaches the spherical mirror in the direction of the center of curvature, it is reflected back on itself, that is, the incident ray is self-conjugated.

4 – Ray incident towards the vertex

When the incident ray reaches the spherical mirror in the direction of the vertex, it is reflected symmetrically about the principal axis.

It is good to pay attention to the fact that in concave mirrors all the reflected rays converge to a single point (focus) situated on the main axis. In convex mirrors all reflected rays diverge, and the extensions of these rays have only one point in common on the principal axis, the focus.

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