Science (086) — AI-generated practice question

A double convex lens is thicker at the middle than at the edges. When parallel rays of light pass through it, both curved surfaces refract the rays inward, bending them toward the principal axis. They converge at a point called the principal focus on the other side. Hence it is called a converging lens.

A double concave lens is thicker at the edges than at the middle. Its inward-curved surfaces refract parallel rays outward, away from the principal axis. The rays appear to diverge from a principal focus on the same side as the incident light. Hence it is called a diverging lens.

Source: Chapter 9, Section 9.3.3 — Refraction by Spherical Lenses

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• Examiners look for: (1) correct description of shape for each lens (where it is thicker), (2) how refraction at the curved surfaces causes convergence or divergence, (3) correct use of terms — converging/diverging, principal focus.
• Avoid just saying "convex converges, concave diverges" — you must explain why using the shape.
• The answer links physical shape → refraction behaviour → naming of lens type, which covers all 3 marks.