Which term describes a lens with one concave and one convex surface?

• A. Plano concave
• B. Meniscus
• C. Bioconvex
• D. Bioconcave

Answer: (B)

A lens with one surface curved inward (concave) and the other curved outward (convex) is called a meniscus lens. This shape is crescent-like because the two surfaces curve in opposite directions, giving a distinctive single-curved profile. Meniscus lenses can be made to act as either converging or diverging lenses depending on which surface has the stronger curvature, and they can be thinner at the center or at the edges accordingly. The other terms describe different configurations: a flat surface plus a concave surface is plano-concave; both surfaces are curved outward is bioconvex; both are curved inward is bioconcave. Therefore, the correct term for one concave and one convex surface is meniscus.