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प्रश्न
Name the defect of vision which can be corrected by a converging lens. Show clearly by a ray diagram how the lens corrects the defect.
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उत्तर
Hypermetropia (long-sightedness) is a defect of vision that can be corrected by using converging lenses. The following ray diagram shows the correction of hypermetropia using a convex lens.
A person with hypermetropia cannot see nearby objects clearly but can see distant objects normally. Fig. (a) shows the near point of the hypermetropic eye, and fig. (b) shows the rays of light from a nearby object forming a blurred image, as the image is formed at a point behind the retina. To correct this defect, convex lenses are used in spectacles, because of which, as illustrated in fig. (c), the rays of light from the nearby object are converged to form a clear and sharp image of the object on the retina.
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संबंधित प्रश्न
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?
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
Name the defect of vision in a person:
whose near point is more than 25 on away.
What is the other name for
myopia
The near-point of a person suffering from hypermetropia is at 50 cm from his eye. What is the nature and power of the lens needed to correct this defect? (Assume that the near-point of the normal eye is 25 cm).
What is short-sightedness? State the two causes of short-sightedness (or myopia). With the help of ray diagrams, show:
(i) the eye-defect short-sightedness.
(ii) correction of short-sightedness by using a lens.
What is long-sightedness? State the two causes of long-sightedness (or hypermetropia). With the help of ray diagrams, show:
(i) the eye-defect long-sightedness.
(ii) correction of long-sightedness by using a lens.
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?
A person can read a book clearly only if he holds it at an arm's length from him. Name the defect of vision:
if the person is an old man
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
Given below is a diagram depicting a defect of the human eye. Study the same and answer the question that follow:
Name the defect shown in the diagram.
List two causes of presbyopia. Draw labelled diagram of a lens used for the correction of this defect of vision.
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:
Give two possible reasons for this defect of the eye in human beings.
Have a look at the posture of this woman who is reading a book and answer the questions which follow:
What kind of looking glasses she needs?
In what two whys is a yellow spot different from the blind spot?
Give Technical Term:
The path which responsible for protecting the eye from sweat.
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.
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.
A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.
When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eye can be corrected?
