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Answer:

Pole: The centre of reflecting surface. It is represented by letter P.

Centre of Curvature: The centre of the sphere of which the mirror forms the part. Represented by “C”.

Radius of Curvature: The radius of the sphere of which the mirror forms the part. Represented by “R”.

Principal axis: The straight line joining the pole (P) and the centre of curvature. It is normal to the mirror at its pole.

Aperture: The diameter of the spherical mirror is called its aperture. The reflecting surface of the mirror.

Focus: The point of the principal axis at which the rays parallel to principal axis meet (concave mirror) or appear to meet (convex mirror) after reflection. Represented by F.

Focal Length: The distance between the pole and the principal focus of a spherical mirror is called focal length. Represented by f.

(i) Pole: It is the middle point P of the spherical mirror.

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

(iii) Radius of curvature: It is the radius R (= AC or BC) of the sphere of which the mirror forms a part.

(iv) Principal axis: The line passing through the pole and the centre of curvature of mirror is called its principal axis.

(v) Linear aperture: It is the diameter AB of the circular boundary of the spherical mirror.

(vi) Angular aperture: It is the angle ACB subtended by the boundary of the spherical mirror at its centre of curvature.

(vii) Principle focus: It is a point F on the principal axis where a beam of light parallel to the principal axis either actually converges to or appears to diverge from, after reflection from a mirror

(viii) Focal length. It is the distance f (= PF) between the focus and the pole of the mirror.