Q1. [2] medium thorough-understanding
While solving a problem using the mirror formula for a concave mirror, a student obtains a positive value for the image distance v. (i) What does the sign of v indicate about the position of the image relative to the mirror? (ii) State the nature (real/virtual, erect/inverted) of this image. (iii) Under what condition of object placement does a concave mirror produce such an image?
Generated by claude-sonnet-4-6 · 2026-06-26 01:13 · grounding rag
Model Answer
(i) A positive value of image distance v indicates that the image is formed behind the mirror (to the right of the pole), i.e., on the same side as the observer.
(ii) The image is virtual and erect.
(iii) This occurs when the object is placed between the pole (P) and the principal focus (F) of the concave mirror.
Source: Light – Reflection and Refraction, Table 9.1 & Sign Convention (Section 9.2.3)
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Explanation
- According to New Cartesian Sign Convention, distances measured to the right of the pole are positive; behind a concave mirror is the right side, so positive v = virtual image behind mirror.
- Table 9.1 directly states: object between P and F → image is behind the mirror, virtual and erect.
- Examiners expect all three parts answered precisely; missing the "erect/inverted" or "real/virtual" loses marks.