Question

 Define (i) principal focus of a concave mirror, and (ii) focal length of a concave mirror.

Answer 1

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.