### Theory:

Spherical mirrors are a part of a sphere. Consider a sphere that is hollow in nature. Consider slicing a portion of a sphere and silvering the surface of the portions on the inner or outer surface, as shown in the below diagram.

**Terms related to spherical mirrors:**

Length AB is the measure of aperture, \(C\) is the centre of curvature, \(P\) is the pole, and \(PC\) is the principal axis.

*Important terms of spherical mirror*

**Aperture**: The portion available for reflection is called aperture; \(APB\) is the aperture.

**Pole**: It is the geometric centre of the reflecting surface. It is denoted by \(P\).

**Centre of Curvature**: It is the centre of the sphere of which the mirror forms a part. \(C\) is the centre of curvature.

**Principal Axis**: It is a straight line passing through the centre of curvature and the pole. The line passing through \(P\) and \(C\) in the figure is the principal axis.

**Radius of Curvature**(\(R\)): It is the radius of the sphere of which the mirror forms a part. \(PC\) is the radius of curvature.

**Principal Focus**: Consider a parallel beam of light incident on a spherical mirror. In the case of a concave mirror, the parallel beam after reflection converges at a point F which is called the principal focus.

In the case of a convex mirror, it appears to diverge from the focus (\(F\)). Thus, a concave mirror is called a converging mirror, and a convex mirror is called a diverging mirror.

**Focal Length**: It is the distance between the pole and the principal focus. \(PF\) is the focal length. It is denoted by ‘\(f\)’. It is measured in \(m\) or \(cm\).