Question

A person is unable to read a book placed closer than \( 1 \text{ meter} \) from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.

Hint:

Remember: \textbf{H}ypermetropia = \textbf{H}arvesting light from \textbf{H}igh distances. Correction uses a \textbf{C}onvex lens (converging).

Answer 1

Identification of the Defect:

If a person is unable to read a book placed closer than 1 metre, it means he cannot see nearby objects clearly. The normal near point of a human eye is about 25 cm. Since his near point has shifted to 1 metre, he is suffering from: \[ \boxed{\text{Hypermetropia (Long-sightedness)}} \]

Reason:
In hypermetropia: – Near objects are not seen clearly.
– The image of a nearby object is formed behind the retina.
– This happens because the eyeball is too short or the eye lens has less converging power.

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Ray Diagram Showing the Defect (Hypermetropia):
For a nearby object, the image forms behind the retina.

Near Object          Eye
    ↑               ______
     \             /      \
      \           /        \
       \         /          \
        \_______/___________( Image forms behind retina )

Explanation: Light rays from a nearby object are not sufficiently converged by the eye lens. Therefore, they meet behind the retina, causing blurred vision.

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Correction of Hypermetropia:
Hypermetropia is corrected by using a convex (converging) lens. The convex lens converges the light rays before they enter the eye, so that the image forms exactly on the retina.

Ray Diagram Showing Correction:

Near Object      Convex Lens        Eye
    ↑               ) (             ______
     \             )   (           /      \
      \           )     (         / Retina \
       \_________)_______(_______/__________\

(Image now forms on retina)

Explanation: – The convex lens converges the diverging rays.
– The eye lens further focuses them on the retina.
– The person can now see nearby objects clearly.

Conclusion:
The person is suffering from hypermetropia. It is corrected by using a convex lens which helps in forming the image of nearby objects on the retina.