A person is unable to read a book placed closer than 1 meter from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
Defect: Hypermetropia (Far-sightedness)
The person cannot read a book closer than 1 m, meaning the near point has shifted beyond 25 cm. This is Hypermetropia.
Cause: The image of a nearby object is focused behind the retina because the focal length of the eye lens is too long or the eyeball is too small.
Ray Diagrams:
Defect:
```
Object → [Hypermetropic Eye Lens] → Image formed BEHIND retina
```
Correction: A convex (converging) lens of suitable power is used. It converges the incoming rays so that the image falls exactly on the retina.
```
Object → [Convex Lens] → [Eye Lens] → Image ON retina
```
The convex lens provides the additional focusing power needed to bring the image onto the retina.
Source: Chapter 10, Section 10.2(b) — Hypermetropia
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Explanation
- The key clue is "cannot read closer than 1 m" — the near point is 1 m instead of the normal 25 cm. This directly indicates Hypermetropia, not myopia.
- Examiners award 1 mark for naming the defect, 1 mark for the defect diagram, and 1 mark for the correction diagram. Label diagrams clearly: show object, lens, retina, and where the image forms.
- Always state the corrective lens type and why it works (provides extra converging power).
- Do not confuse with Myopia (distant objects blurred, corrected by concave lens).