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

Step 1: Understanding the Concept:
A person who can see distant objects clearly but cannot see nearby objects distinctly is suffering from Hypermetropia.
The near point of the eye moves away from the normal near point (\( 25 \text{ cm} \)).
Step 2: Detailed Explanation:
Defect: Hypermetropia.
Causes:
1. The focal length of the eye lens is too long.
2. The eyeball has become too small.
In this defect, light rays from a nearby object are focused at a point behind the retina.
Correction:
It is corrected by using a convex (converging) lens of appropriate power.
The convex lens provides additional focusing power so that the image is formed exactly on the retina.
Step 3: Ray Diagrams:
1. Hypermetropic Eye: Rays from the normal near point (\( N \)) at \( 25 \text{ cm} \) meet behind the retina.
2. Corrected Eye: A convex lens creates a virtual image of the object (placed at \( 25 \text{ cm} \)) at the person's actual near point (\( 1 \text{ m} \)), allowing the eye to focus it on the retina.
Step 4: Final Answer:
The defect is Hypermetropia, corrected using a convex lens.