The eyes of a person are focused (i) on a nearby object, and (ii) on a distant object, turn by turn. In which case:(a) the focal length of eye-lens will be the maximum?(b) the converging power of eye-lens will be the maximum?

(a) The focal length of the eye lens is the maximum when the eyes of a person are focused on a distant object.

(b) The converging power of eye-lens will be the maximum when the eyes of a person are focused on a nearby object.

Explanation

When the eye is focusing on a distant object, the eye lens gets stretched and becomes thinner because, while focusing on a distant object, the ciliary muscles of the eyes are fully relaxed pulling the suspensory ligaments attached to the eye lens tightly. Since these ligaments become tight, they pull the eye lens, due to which the eye lens becomes thinner (or less convex) so as to decrease its converging power. Since the converging power gets decreased or small, the thin eye lens is sufficient to converge the parallel light rays coming from a distant object to form an image on the retina.

When the eye is focusing on a nearby object, the eye lens bulges and becomes thicker because, while focusing on a nearby object, the ciliary muscles of the eyes contract, loosening the suspensory ligaments attached to the eye. Since these ligaments become loose, they stop pulling the eye lens, due to which the eye lens bulges under its own elasticity and becomes thick (or more convex) so as to increase its converging power. Since the converging power gets increased, the thick eye lens can converge the diverging light rays coming from the nearby object to form an image on the retina.