Final answer:
A light ray approaching a lens from the focal point comes out parallel to the principal axis, according to a key rule governing the behavior of converging lenses.
Step-by-step explanation:
If a light ray approaches a lens from the focal point, it comes out parallel to the principal axis. When dealing with a converging lens, this is one of the key rules that govern its behavior. Specifically, Rule 4 for light behavior states that a ray entering a converging lens through its focal point exits parallel to its axis.
It's important to note that this principle also applies in reverse: if a light ray enters a converging lens parallel to the principal axis, it will pass through the focal point on the other side of the lens. This symmetry is a fundamental aspect of lens behavior and is invaluable in understanding how lenses focus light.