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प्रश्न
What change is made in the eye to enable it to focus on objects situated at different distances? Illustrate your answer with the help of diagrams.
उत्तर
a) When the eye is focussed on a nearby object, the ciliary muscles of the eye contract, loosening the suspensory ligaments attached to the eye. As the ligaments become loose, they stop pulling the eye lens, because of which the eye lens bulges (or becomes more convex), increasing its converging power. As the converging power increases, the eye lens converges the diverging rays of light from the nearby object to form its image on the retina.
(b) When the eye is focussed on a distant object, the ciliary muscles are completely relaxed. The relaxed ciliary muscles pull the suspensory ligaments tightly. As the ligaments become tight, they pull the eye lens, because of which the eye lens becomes thinner (or less convex). The focal length of the eye lens is the maximum but its converging power is the minimum. However, the small converging power is enough to converge the parallel light rays from the distant object and form its image on the retina.
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संबंधित प्रश्न
A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads :
Left eye : +2.50 D
Right eye : +2.00 D
Which lens bends the light rays more strongly?
What is the:
near point of a normal human eye?
Give the scientific names of the following parts of the eye:
carries signals from an eye to the brain.
Refraction of light in the eye occurs at:
(a) the lens only
(b) the cornea only
(c) both the cornea and the lens
(d) the pupil
What shape are your eye-lenses:
when you look at a distant tree?
After testing the eyes of a child, the optician has prescribed the following lenses for his spectacles:
Left eye : + 2.00 D
Right eye : + 2.25 D
The child is suffering from the defect of vision called:
(a) short-sightedness
(b) long-sightedness
(c) cataract
(d) presbyopia
Name the following:
The part of the eye responsible for change in the size of the pupil.
Give Technical Term:
The nutritive layer of the eye which also presents reflection of light.
Write the name.
The part of human eye that transmits electrical signals to the brain.
Assertion: Blind spot is a small area of the retina which is insensitive to light where the optic nerve leaves the eye.
Reason: There are no rods or cones present at the junction of the optic nerve and retina in the eye.
