What type of lens surface has positive power?

The correct choice for identifying a lens surface with positive power is the convex lens. A convex lens is defined by its outward-curving shape, which causes light rays that pass through it to converge or focus at a point. This focusing effect is due to the lens' ability to bend the light rays inwards toward the principal axis.

In optical terms, lenses with positive power are those that converge light, and a convex lens is the classic example of such a lens. The positive power of a convex lens allows it to magnify images and is often used in applications like magnifying glasses, cameras, and corrective eyewear for hyperopia (farsightedness).

In contrast, other lens types either diverge light (such as concave lenses, which possess negative power), maintain no curvature (as seen in planar lenses), or address specific conditions like astigmatism (as with cylindrical lenses). Thus, the distinction lies in the light-converging properties of the convex lens, giving it positive optical power.