State the rules used fro drawing ray diagrams for the formation of an image by a concave lens.

Explanation

(1) When the incident ray parallel to the principal axis, the refracted ray, when extended backwards, passes through the principal focus.
(2) When the incident ray is directed towards the principal focus `F_(2)`, the refracted ray is parallel to the principal axis.
(3) When the incident ray passes through the optical centre of the lens, it passes without changing its direction.