Reflection through spherical surface:
Centre of curvature: The centre of a hollow sphere of which the curved spherical mirror forms a part is called centre of curvature. It is denoted by C.
Radius of curvature: The radius of a hollow sphere of which the curved spherical mirror forms a part is called radius of curvature. It is denoted by R = PC.
Pole: The middle point of a spherical mirror is called pole. It is denoted by P.
Aperture: The part of a spherical mirror exposed to the incident light is called the aperture of the spherical mirror. It is the diameter of the spherical mirror. It is denoted by XY.
Principle axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror is called principle axis.