Define the following terms in the context of spherical mirrors :
(i) Pole
(ii) Centre of curvature
(iii) Radius of curvature
(iv) Principal axis
(v) Principal focus

Explanation

(i) Pole : The centre of the reflecting surface of a spherical mirror.
(ii) Centre of curvature : The reflecting surface of a spherical mirror is part of a sphere. The centre of that centre of that sphere is called centre of curvature.
(iii) Radius of curvature : The radius of the sphere from which a mirror is made.
(iv) Principal axis : An imaginary line passing through the pole and the centre of curvature. The principal axis is normal to the mirror at the pole.
(v) Principal focus : The point on the principal axis, at which incident light rays parallel to the principal axis converge or appear to diverge froms, is called the principal focus of the lens.