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The eye lens is composed of a fibrous, jelly-like material. To see closure and distant object, Its focal length can me changed to certain extent by contraction and relaxation of ciliary muscles. The ability of the eye lens to adjust its focal length by contracting and relaxing its ciliary muscles is called accommodation. To see closer object, ciliary muscles, must decrease the focal length of eye lens. However, the focal length of the eye lens cannot be decreased below a certain minimum limit. To see an object comfortably and distinctly, the distance of object should be at least 25 cm from the eyes. Due to this, a normal eye is not able to see clearly the objects placed closer than 25 cm. This distance at which objects can be seen is clearly, is called the least distance of distinct vision or the near point of the eye.
Source: Ncert
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Answer:
A normal eye has a near point of 25 cm. This means that the eye can focus near objects present at least 25 cm away from the eyes.
Why is it so ?
This is because of the following reason:
1. Accomodation in the eye is accomplished with the help of ciliary muscles and lens.
2. In order to focus near objects, the eye lens has to become more convex and decrease it's focal length. This is done by relaxation of the ciliary muscles and suspensory ligaments.
3. If an object is placed too near to the eye (less than 25 cm) , the lens is unable to become that much convex . It is unable to increase it's POWER to that extent.
4. Hence it is unable to focus .