Focus of a spherical mirror

Convex spherical mirrors are widely used for surveillance and security, being present in stores, supermarkets etc.

In the initial studies of spherical mirrors we see that a spherical cap is a part of a spherical surface bounded by a plane. We also see that a spherical mirror is any reflecting surface in the form of a spherical cap, very well polished, capable of regularly reflecting light, internally or externally. If this polishing is from the inner part of the cap, we will obtain what we call a concave spherical mirror; if the outside is polished, we will obtain a convex spherical mirror.

We can observe this type of mirror in different places, such as, for example, in grocery stores, inside public transport buses, etc. This type of mirror has the following elements: center of curvature, radius of curvature, vertex, main axis, secondary axis and aperture angle.

If we make a ray of light incident parallel to the principal axis of a concave spherical mirror, we will see that this reflected ray (or rays) will converge to a single point, called the principal focus . Let’s see the figure below:

According to the figures above, we can see that in the concave mirror the focus is real, that is, there is an effective crossing of rays in front of the mirror, while in the convex mirror the focus is virtual because it is obtained by extending the rays behind. from the mirror.

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