凸面

1. Origins, structure, and basic meaning

• Structure: 凸面, read とつめん, is a noun for a surface that curves outward.
• Basic usage: 凸面が光を反射する makes the convex face the reflector; 凸面を上に向ける makes it the face oriented upward.

2. Common pitfalls and similar expressions

• An outward-curving surface
  • 凸面 curves outward and contrasts with 凹面. Reflected light spreads in different directions from such a surface rather than behaving as it would on a flat face.