What is the main characteristic of a concave surface?

A concave surface is defined by its inward curvature, resembling the interior of a bowl or a cave. This characteristic causes light to diverge after it strikes the surface, which is particularly important in optics, as it influences how images are formed and light is transmitted through optical instruments like lenses.

In terms of application, concave surfaces are used in various optical devices such as telescopes, mirrors, and certain types of lenses to focus light. The inward curve allows these devices to manipulate light properties effectively, making it essential for the design of optical systems.

The alternatives – an outward curvature, a flat surface, and an angled surface – do not accurately describe the defining characteristic of concavity. An outward curvature is indicative of a convex surface, while a flat surface lacks any curvature, and an angled surface represents a specific geometric configuration that is not related to the concave definition. Thus, the inward curvature is what distinctly identifies a concave surface.