At which single position of the object in front of a concave mirror does the image form at the same location as the object? Justify your answer.
Generated by claude-sonnet-4-6 · 2026-06-26 01:12 · grounding rag
Model Answer
When the object is placed at the centre of curvature (C) of a concave mirror, the image forms at the same position — also at C.
Justification: A ray passing through C strikes the mirror along the normal and reflects back along the same path. The reflected rays meet exactly at C, forming a real, inverted image of the same size as the object at C itself.
Source: Chapter 9, Section 9.2.2 — Image formation by Concave Mirror
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Explanation
- The key fact is object at C → image at C (same position).
- The justification comes from ray property (iii): a ray through the centre of curvature reflects back along the same path because it hits the mirror perpendicularly (along the normal).
- Examiners expect both the position AND a reason — that's why it's 2 marks (1 for position, 1 for justification).
- Mention the image nature (real, inverted, same size) for completeness, though it is not strictly required by the question.