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(a)

(i) Pole- The centre of the spherical mirror is called pole represented by P.

(ii) Centre of curvature- it is the centre of the hollow sphere of glass of which the mirror is the part. Represented by C, the centre of curvature of concave mirror is in front but the centre of curvature of convex mirror is at its back.

(iii) Principal axis- of a spherical mirror is the straight line joining the centre of curvature and pole of the mirror. The principal axis is normal to the mirror at the pole.

(iv) Principal focus- it is a point on the principal axis of the spherical mirror at which the light rays which are parallel to the principal axis converge or appear to diverge after reflection.

(b) Ray diagrams of principal focus:

(i) Concave mirror: The principal focus of concave mirror is the point on the principal axis to which all the light rays which are parallel and close to axis converge after reflection. Thus, concave mirror has a real principal focus and it lies in front of the mirror.

(ii) Convex mirror: In a convex mirror, the reflected rays do not actually pass through the focus (F), they appear to diverge. Thus, a convex mirror has a virtual principal focus situated behind the mirror.

(c) The mirror used in the given diagram is a concave spherical mirror. Image formed (Q) is virtual, erect and magnified.