f.3 physics (lens)

First, the light ray that passes through the optical centre of the lens is not refracted.

For the other light ray, because parallel light rays, after refraction at a concave lens (divergent lens), must meet, after producing the rays backward, at a point on the focal plane. If the light rays are parallel to the principal axis, then after passing through the lens and producing backward, they will meet at the principal focus. Now the light rays are inclined at an angle to the principal axis, hence the meeting point will be elevated upward along the focal plane.

Note: a focal plane is a plane parallel to the lens that contains the principal focus.