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प्रश्न
List two causes of presbyopia. Draw labelled diagram of a lens used for the correction of this defect of vision.
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उत्तर
Causes of presbyopia :
Aging
Weakening of ciliary muscles
It is treated by using a bifocal lens both concave and convex.
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संबंधित प्रश्न
What is myopia?
A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
Name any two defects of vision which can be corrected by using spectacles.
A man can read the number of a distant but clearly but he finds difficulty in reading a book.
What type of spectacle lens should he use to correct the defect?
A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.
Name the type of defect he is suffering from.
The near point of a long-sighted person is 50 cm from the eye.
(a) Can she see clearly an object at:
(i) a distance of 20 cm?
(ii) at infinity?
When do we consider a student sitting in the class to be myopic? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.
Name the common defects of the eye.
Give Technical Term:
The path which responsible for protecting the eye from sweat.
Assertion: Concave mirrors are used as reflectors in torches, vehicle head lights and in search lights.
Reason: When an object is placed beyond the center of curvature of a concave mirror, the image formed is real and inverted.
