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Chapter – 11 The Human Eye and the Colourful World
Q 1. What is meant by power of accommodation of the eye?
Ans. The ability of the eye lens to adjust its focal length, so as to clearly focus rays coming from distant as well a near objects on the retina, is called the power of accommodation of the eye. Q2. 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?
Ans. A person with a myopic eye should use a concave lens of focal length 1.2 m so as to restore proper vision. Q 3. What is the far point and near point of the human eye with normal vision? Ans. For a human eye with normal vision the far point is at infinity and the near point is at 25 cm from the eye. Q 4. A student has difficulty 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. The student is suffering from myopia or short-sightedness. The defect can be corrected by the use of concave (diverging ) lens of an appropriate power.
Q 5. The human eye can focus objects at different distance 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) accommodation.
[ Hint: While seeing distant object eye lens is thinner and its focal length is more (about 2.5 cm). While looking near objects eye lens assumes a more round shape, its focal length decreases and nearly objects are clearly focussed at the retina.]
Q 6. The...