Video Transcript
The diagram below shows a light ray, in red, heading toward a convex lens. Is the light ray parallel to the optical axis of the lens?
This question asks us whether this ray, shown in red in the diagram, is parallel to
the optical axis of the lens. First, let’s note that the lens here is a convex lens. We can remember that a convex lens can be formed by overlapping two spheres. Note that in two dimensions, this looks like overlapping the area of two circles.
Now, let’s remember that the optical axis is the line that passes through the two
centers of curvature of the lens and also through the center of the lens itself. The lens’s centers of curvature are the centers of the two circles we have drawn. So, the optical axis is this line here.
Looking at the light ray in this diagram, we can draw in a line parallel to the
optical axis at the height of this ray. We can observe that the ray forms an angle 𝛼 with the optical axis that is not equal
to zero degrees. This means that the light ray is not parallel to the optical axis.
Therefore, our answer to this question is no, the light ray in the diagram is not
parallel to the optical axis of the lens.
