A student places a candle at various positions in front of a convex lens and tries to catch the image on a screen. At one particular position of the candle, no image can be formed on the screen, yet an image does exist. Where is the candle, and why can the image not be caught on a screen?
Generated by claude-sonnet-4-6 · 2026-06-26 01:15 · grounding rag
Model Answer
The candle is placed between the focus F₁ and the optical centre O of the convex lens.
When the object is placed between F₁ and O, the refracted rays diverge on the other side of the lens — they do not actually meet, but appear to diverge from a point on the same side as the object. The image formed is virtual, erect, and enlarged.
Since the rays only appear to diverge (they never actually converge), a screen cannot catch this image. It can only be seen by looking through the lens directly.
Source: Chapter 9, Table 9.4 — Image Formation by Lenses
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Explanation
- The key fact from Table 9.4: when object is between F₁ and O → image is virtual, erect, enlarged, on the same side as the object.
- Why no screen? A screen can only catch a real image (where rays actually meet). A virtual image is formed by the backward extension of diverging rays, so it cannot be projected.
- Examiners expect: correct position of candle + reason linked to virtual/diverging rays. Both parts are necessary for full marks.