What is the focal point of a lens?

The focal point of a lens is defined as the location where rays of light that are initially parallel to the lens's axis either converge to a single point or appear to diverge from a single point after passing through the lens. This point is critical in understanding how lenses function in applications such as cameras, glasses, and microscopes.

In a convex lens, parallel light rays entering the lens converge at the focal point on the opposite side. Conversely, a concave lens causes parallel rays to spread out as if they originated from the focal point located on the same side as the incoming light. This unique property of lenses to focus or disperse light is essential for forming images and is what distinguishes the focal point as an important concept in optics.

The other options do not accurately represent the focal point's definition. Light absorption, the lens's position within a frame, and the distance from the lens to the image are related to different aspects of optics but do not describe the focal point itself.