The heat produced at a point due to concentration of sunlight by a convex lens burns a paper.
Generated by claude-sonnet-4-6 · 2026-06-15 06:49 · grounding rag
Model Answer
(a) A convex lens converges the parallel rays of sunlight to a sharp bright point on the paper. The concentration of sunlight at that point generates a large amount of heat, which causes the paper to burn.
(b) The point is called the principal focus (F) of the convex lens. The bright spot formed on the paper represents a real image of the Sun.
Source: Chapter 9, Section 9.3.3 (Activity 9.11)
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Explanation
- (a) The key idea is convergence of parallel rays + heat generation — both must be mentioned for full credit.
- (b) Examiners expect the exact term "principal focus" and the fact that the bright spot is a real image of the Sun (not just "an image"). These two facts are explicitly stated in Activity 9.11 of the textbook.