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The Human eye and the colourful world, 1), , What is meant by the power of accommodation of the eye?, , Ans : The term "power of accomodation" of the human eye refers to the, process by which the ciliary muscles function, to adjust the focal length, (or converging power) of the eye lens so as to focus both near and, distant objects clearly on the retina., OR, The term "power of accommodation" of the human eye refers to the, ability or the property of the eye lens to adjust its focal length ( or, converging power ) with the help of ciliary muscles in order to be able to, focus both near and distant objects clearly on the retina., , t, , 2), A person with a myopic eye cannot see objects beyond 1.2 m, distinctly. What should be the type of the corrective lens used to restore, proper vision?, , ra, , Ans : The proper vision of a myopic eye can be restored by using, concave lens of suitable power., 3), What are the far point and near point of the human eye with normal, vision?, , S, , Ans : The maximum distance upto which the eye can see objects clearly, is called the far point of the eye. The far point for an eye with normal, vision is infinity., The near point of the eye is the minimum distance of the object from the, eye that can be seen without strain. For a human eye with normal, vision, the near point is usually 25 cm., 4), A student has difficulty in reading the blackboard while sitting in the, last row. What could be the defect the child is suffering from? How can, it be corrected?, Ans : Since the student has difficulty reading the blackboard while sitting, in the last row, he is most likely to suffer from the disease of myopia, (short-sightedness)., Hence it can be corrected by using spectacles with concave lenses of, appropriate power.
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5) The human eye can focus objects at different distances by adjusting, the focal length of the eye-lens. This is due to:, (a) Presbyopia, (b) Accommodation, (c) near-sightedness, (d) far-sightedness, Ans : (b) Accomodation, 6) The human eye forms the image of an object at its:, (a) Cornea, (b) Iris, (c) Pupil, (d) Retina, Ans : (d) Retina, , (a), (b), (c), (d), , 25 m, 2.5 cm, 25 cm, 2.5 m, , ra, , vision is about:, , t, , 7) The least distance of distinct vision for a young adult with normal, , Ans : (c) 25 cm., 8) The change in focal length of an eye-lens is caused by the action of :, , S, , (a) Pupil, (b) Retina, (c) ciliary muscles, (d) iris., , Ans : (c) ciliary muscles.
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9) Make a diagram to show how hypermetropia is corrected., , ra, , t, , Ans :, , 10) Why is a normal eye not able to see clearly the objects placed closer, than 25 cm?, , S, , Ans : When objects are placed closer than 25 cm, all power of, Accomodation of the eye is already exhausted and the ciliary muscles, cannot make the lens more thick to focus the image on retina. Hence, a, normal eye cannot see objects closer than 25 cm clearly. Under such, conditions, the object appears blurred and produces strain in the eyes., 11) What happens to the image distance in the eye when we increase the, distance of an object from the eye?, Ans : When we increase the distance of an object from the eye, the focal, length of the eye lens accommodates itself in such a way that a clear, image is always formed on the retina. Thus the increase in the object, distance is compensated by the change in the focal length of the eye, lens. Therefore, the image distance in the eye remains the same even, when the object distance is varied.
