(a) Define (i) principal focus of a concave mirror, and (ii) focal length of a concave mirror.
(b) Draw diagram to represent the action of a concave mirror on a beam of parallel light rays. Mark on this diagram principal axis, focus F, centre of curvature C, pole P and focal length f, of the concave mirror.

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Solution

(a) Definitions-
(i) Principal focus (F) of a concave mirror – Focus of a concave mirror is the point at which the incident rays, parallel to the principal axis, actually meet after reflecting from the concave mirror.
(i) Focal length (f) – Focal length of a concave mirror may be defined as the distance between its focus and pole.
(b) Ray Diagram-

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