Explain the first focal point and second focal point for a lens.

(N/A) $(i)$ First focal point: It is the position of an object on the principal axis such that the rays of light originating from it become parallel to the principal axis after refraction through the lens. It is denoted by $F_{1}$.
$(ii)$ Second focal point: It is the position of a point-like image on the principal axis formed by the lens when the incident rays of light are parallel to the principal axis. It is denoted by $F_{2}$.