Lightrays Falling on a Convex Lens
We just observed how a convex lens bundles the light rays from the sun into a single bright spot. This means that a convex lens refracts light in a very special way, as this graphic will illustrate. It shows a lens from the side, and light rays coming in from the left. Rays near the middle of the lens are not changing direction very much. But rays that hit the lens closer to its rim are bent much more, such that all rays meet in one point, the focal point of the lens. The distance between the lens and the focal point is called the focal length of the lens. As we have shown in our experiment in the sun, a thicker lens has a shorter focal length than a thinner lens.