Which type of lens is thicker in the center than at the edges?

• A. Concave lens
• B. Convex lens
• C. Flat lens
• D. Bifocal lens

Answer: (B)

A convex lens is thicker in the center than at the edges. This shape causes light rays that enter parallel to the principal axis to converge at a focal point on the opposite side of the lens. The reason a convex lens has this structure is due to its ability to bend light inward, concentrating it for purposes such as magnifying objects or correcting vision for far-sightedness. The curvature of the lens is essential for its optical properties, allowing it to create a real image or an enlarged virtual image depending on the position of the object relative to the focal length.

In contrast, a concave lens is thinner in the center and thicker at the edges, leading to the divergence of light rays. A flat lens has a uniform thickness throughout and cannot focus or disperse light effectively, while a bifocal lens combines two different types of lenses but does not specifically feature a thicker center. Therefore, the defining characteristic of the convex lens in this context is its thicker center, which facilitates the convergence of light.