Question

What happens to a light ray traveling parallel to the optical axis of a convex lens that passes through the lens?

Answer 1

Also called Principal axis.

Explanation:

As shown in the ray diagram above; all rays, except one, which are parallel to the optical axis, while passing through the lens are refracted and thereafter pass through the Principal Focus F on the other side of the lens.

Exception is the ray which passes through the optical center. This ray does not get refracted. It crosses the lens straight then to pass through the same focal point F.