Why is normal eye not able to see clearly the objects placed closer than 25 cm ?

With the help of ciliary muscles the human eye can change its curvature and thus alter the focal length of its lens. State the changes that occur in the curvature and focal length of the eye lens while viewing (a) a distance object, (b) nearby objects. Explain, why a normal eye is not able to see distincly the objects placed closer than 25 cm, without putting any strain on the eye.

A normal eye is not able to see objects closer than 25 cm because

A person cannot see the objects distinctly, when placed at a distance less than 100 cm . What is the power of the spectacles that he should use to see clearly the objects placed at 25 cm ?

A person cannot see the objects distinctly, when placed at a distance less than 100 cm . What is the power of the spectacles that he should use to see clearly, the objects placed at 25 cm ?