The area of the lens where light rays can pass through without deviation is called what?

• A. Focal point
• B. Optical center
• C. Nodal point
• D. Vertex

Answer: (B)

In optics, the important idea here is the optical center—the point inside a lens through which light can pass without bending. In a thin-lens model, any ray that goes through the optical center emerges undeviated, meaning it continues in the same direction as it entered. That’s why, when drawing ray diagrams, you can route a ray through the optical center and treat it as unchanged by refraction. The optical center isn’t about a broad area; it’s a specific point (often near the geometric center of the lens) that defines where light passes straight through. Focal points are where rays converge after refraction, nodal points relate to preserving ray angles through thicker lenses, and the vertex is simply the point where the lens surface meets the optical axis.