A student can read the school notice board from across the room but struggles to read his textbook unless he holds it at arm's length. (a) Identify the defect of vision he has. (b) State TWO possible structural reasons for this defect. (c) What kind of corrective lens should he use?
Generated by claude-sonnet-4-6 · 2026-06-26 01:07 · grounding rag
Model Answer
(a) Defect of Vision:
The student has Hypermetropia (far-sightedness). He can see distant objects (notice board) clearly but cannot see nearby objects (textbook) without holding them far away.
(b) Two Structural Reasons:
- The focal length of the eye lens is too long.
- The eyeball has become too small.
(c) Corrective Lens:
A convex lens (converging lens) of appropriate power should be used. It provides the additional focusing power needed to form the image on the retina.
Source: Chapter 10, Section 10.2 – Hypermetropia
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Explanation
- The key clue is that the student struggles with near vision (textbook) but not distant vision (notice board) — this is the classic sign of hypermetropia, not myopia.
- Examiners expect you to name both the defect and its common name.
- The two structural causes must be stated as given in the textbook — focal length too long OR eyeball too small.
- Always specify convex (not just "a lens") for hypermetropia; concave is for myopia. Getting this reversed is a common mistake.