Bioconvex is the term for a lens with:

• A. One surface concave, the other convex
• B. One surface flat, the other convex
• C. Both surfaces convex
• D. Both surfaces concave

Answer: (C)

Bioconvex describes a lens with two convex surfaces. With both faces bulging outward, the lens is thicker in the middle than at the edges, so it acts as a converging lens when light passes through. Parallel rays entering the lens are bent toward the axis and focus to a point on the other side, giving a positive focal length. This is why the correct description is a lens that has two outward-curving faces. Other shapes describe plano-convex (one flat, one curved), a meniscus lens (one concave and one convex surface, which can converge or diverge depending on curvature), or a biconcave lens (both surfaces concave, which diverges light).