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प्रश्न
The picture given here shows a person wearing 'half-moon' spectacles. What sort of eye-defect do do you think he has? Why are these particular spectacles useful to him?
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उत्तर
As the person is wearing half-moon spectacles, he should be suffering from the eye defect called long-sightedness, or hypermetropia, because his spectacles are fitted with convex lens. The convex lenses form the images of nearby objects at the near point of his eye, and he can, therefore, see these objects clearly.
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संबंधित प्रश्न
What is the far point and near point of the human eye with normal vision?
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Name the defect of vision in a person:
whose far point is less than infinity
Name the defect of vision in which the eye-lens loses its power of accommodation due to old age.
What is the other name of old age hypermetropia?
An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short-sighted?
A short-sighted person has a near point of 15 cm and a far point of 40 cm.
(a) Can he see clearly an object at a distance of:
(i) 5 cm?
(ii) 25 cm?
(iii) 50 cm?
(b) To see clearly an object at infinity, what kind of spectacle lenses does he need?
Differentiate between members of the following pair with reference to what is asked in bracket.
Myopia and hyperopia (cause of the defect)
What is meant by optical illusion? Give one example.
A person is unable to read a book placed closer than 1 meter from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.
What is Hypermetropia (far sightedness)?
Rewrite the following table so as to match second and third column with first column.
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Column I
|
Column II
|
Column III
|
|
(i) Myopia
|
Old age problem
|
Bifocal lens
|
|
(ii) Presbyopia
|
Nearsightedness
|
Concave lens.
|
A person is unable to see objects distinctly placed within 50 cm from his eyes.
(a) Name the defect of vision the person is suffering from and list its two possible causes.
(b) Draw a ray diagram to show the defect in the above case.
(c) Mention the type of lens used by him for the correction of the defect and calculate its power. Assume that the near point for the normal eye is 25 cm.
(d) Draw a labeled diagram for the correction of the defect in the above case.
Name the common defects of the eye.
Give Reason:
Why do we see clearly in the central region of the retina?
Give Reason:
When you enter into a dark room from bright because of sunlight, you can not see things for a few seconds.
Given below is a diagram showing a defect of vision. Name the defect of vision and draw an accurately labelled diagram to correct this defect.
Observe the figure whether it is correct or not and explain the phenomenon.
