To instruct a ray diagram, we use two light rays which are so chosen that it is easy to know their directions after refraction from the lens. List these two rays and state the path of these rays after refraction. Use these two rays to locate the image of an object placed between F and 2F of a convex lens.
Two rays choose for refraction:
(i) A ray of light parallel to the principal axis.
(ii) A ray of light passing through the optical centre of a lens.
Path of these rays after refraction:
In case of convex lens, the first ray will pass through the principal focus on the other side of the lens.
In case of concave lens, the first ray will
(a) appear to diverge or
(b) appear to come from the principal focus positioned on the same side of the object.
The second ray emerge from the lens without any deviation in the path.