Important term for concave mirror :
(a) Pole: The centre of a spherical mirror’s reflecting surface is called the pole.
It lies on the surface of the mirror and it is denoted by P.
(b) Center of curvature: The centre of the sphere formed by a spherical mirror’s reflecting surface is known to as the centre of curvature. It is denoted by C. This is outside of mirror’s the reflecting surface and is not a part of the mirror. It is in front of the mirror and is concave.
(c) Radius of curvature: it is the radius of the spherical mirror formed by the reflecting part of the sphere. It is represented by R.
(d) Principal axis: it is the straight line passing through the pole and centre of curvature of the spherical mirror. This is normal for the mirror at its pole.
(e) Principal focus: the incident rays coming parallel to the principal axis after reflection appear to converge to a common point on the principal axis, this point is called the principal focus of a concave mirror. It is usually denoted by F.
(f) Focal length: it is the distance between the pole and the principal focus of the concave mirror. It is denoted by f.
