CBSE Class 10 Science 2017 · Paper 31/1/1/C · Question 20

The defect is hypermetropia (far-sightedness, or long-sightedness): nearby objects cannot be seen distinctly while distant objects can, because the near point of the eye has moved farther than 25 cm. Ray diagram of the defect: rays from an object at the normal near point $N$ (25 cm) are not converged enough by the eye lens and would meet at a point behind the retina; the nearest object this eye can focus on the retina is at its own near point $N^{\prime }$, farther away. Two possible causes: (i) the focal length of the eye lens is too long (its converging power is too small); (ii) the eyeball has become too small. Correction: a convex (converging) lens of suitable focal length is used in front of the eye. It forms a virtual image of an object at 25 cm at the near point $N^{\prime }$ of the person, so the rays seem to come from $N^{\prime }$ and the eye focuses them on the retina.