Define the following terms in relation to a concave spherical mirror (any five):
$(i)$ Pole
$(ii)$ Centre of curvature
$(iii)$ Radius of curvature
$(iv)$ Principal axis
$(v)$ Principal focus
$(vi)$ Aperture
$(vii)$ Focal length

(N/A) $(i)$ Pole (Vertex): The central point of the reflecting surface of a spherical mirror is called its pole.
$(ii)$ Centre of curvature: The centre of the sphere of which the mirror is a part is called the centre of curvature.
$(iii)$ Radius of curvature: The radius of the sphere of which the mirror is a part is called the radius of curvature.
$(iv)$ Principal axis: The straight line passing through the pole and the centre of curvature of the mirror is called the principal axis.
$(v)$ Principal focus: It is a point on the principal axis where light rays parallel to the principal axis converge or appear to diverge after reflection.
$(vi)$ Aperture: The effective diameter of the light-reflecting area of the spherical mirror is called its aperture.
$(vii)$ Focal length: The distance between the pole and the principal focus of a spherical mirror is called the focal length,represented by $f$.