Terms Related to Spherical Mirror

The words 'reflection' and 'mirror' go almost hand in hand in our mind

Mirrors greatly help us to understand the concept of reflection, image-formation etc

Plane mirror forms image which is at a same distance from the mirror, as the object

Spherical mirrors however have it's image distances varying with different positions for the object

To understand the relation between object distance and image distance, we need to be familiar with few terms of spherical mirror.

Concave mirrors are made out of hollow spherical glass whose outer surface is silvered

Whereas convex mirrors are made out of hollow spherical glass whose inner surface is silvered

Important terms related to spherical mirror

The centre of the hollow spherical glass, of which the mirror is a part is called the Centre of Curvature ()

The radius of the glass sphere is called the Radius of Curvature ()

Pole () is the central point of the reflecting surface of the mirror

Aperture () is the exposed part of the spherical mirror upon which light is incident. In the fig, MM' is the aperture.

The line joining the Pole and the Centre of Curvature is called the Principal Axis ().

Rays of light parallel to the principal axis are either converged or appear to diverge from a point, after reflection from the mirror

In case of a concave mirror, the light rays are converged to a point. This point is known as the Principal Focus

Whereas, in case of a convex mirror, the light rays appear to diverge from a point. This point is also known as the Principal Focus ()

Revision

The centre of the hollow spherical glass of which the mirror is a part off is called the Centre of Curvature ()

The radius of the hollow spherical glass of which the mirror is a part of is called the Radius of Curvature ()

Aperture () is the exposed part of the mirror whereas Pole () is the central point of the mirror

The line joining the Pole and the Centre of Curvature is called the Principal Axis (). It is extended on both the sides

Rays of light parallel to the principal axis are either converged or appear to diverge from a point, after reflection from the mirror

In case of a concave mirror, the light rays are converged to a point. This point is known as the Principal Focus

Whereas, in case of a convex mirror, the light rays appear to diverge from a point. This point is also known as the Principal Focus ()

The End