Question

Draw a ray diagram to show the correction of eye defect of an old man who cannot see an object placed closer than 1 m from his eye clearly.

Hint:

Cannot see near objects → Use convex lens (hypermetropia correction).

Answer 1

Correction of the Eye Defect of an Old Man Who Cannot See Objects Placed Closer Than 1 m Clearly

If an old man cannot see objects placed closer than 1 m clearly, he is suffering from Hypermetropia (Long-sightedness). In this defect, the near point of the eye has shifted from the normal 25 cm to 1 m.

Reason of the Defect:
– The eye lens loses its power of accommodation due to aging.
– The focal length of the eye lens increases.
– Nearby objects are focused behind the retina instead of on the retina.

Correction:
This defect is corrected by using a convex (converging) lens. The convex lens converges the light rays coming from a nearby object so that the image is formed at the near point (1 m), enabling the eye to focus it clearly on the retina.

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Ray Diagram (Correction of Hypermetropia):

   Object          Convex Lens              Eye Lens              Retina
     O                  )(                    ()                  | 
     |\                /  \                  /  \                 |
     | \______________/    \________________/    \________________|
         (Light rays are first converged by convex lens,
          then properly focused on the retina.)
  

Explanation of Ray Diagram:
1. Light rays from a nearby object are diverging.
2. The convex lens converges these rays before they enter the eye.
3. The eye lens then focuses the rays exactly on the retina.
4. Thus, a clear image is formed.

Conclusion:
An old man who cannot see objects closer than 1 m clearly suffers from hypermetropia. This defect is corrected by using a convex lens, which helps in forming a clear image on the retina by increasing the converging power of the system.