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प्रश्न
Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.
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उत्तर
Myopia (short-sightedness) is a defect of vision that can be corrected by using diverging or concave lenses. The following ray diagram clearly shows the correction of myopia by using a diverging lens.
A person with myopia does not see distant objects clearly but has normal near vision. Fig. (a) shows the far point of the myopic eye, and fig. (b) shows the parallel light rays from a distant object forming an image at a point in front of the retina. To correct this defect, a concave lens is used, because of which, in fig. (c), we observe the rays being diverged first so that they form a clear image on the retina.
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संबंधित प्रश्न
Given below is a diagram showing a defect of human eye. Study it and answer the following questions.
(i) Name the defect shown in the figure.
(ii) Give reason for this defect of eye in human being.
(iii) Name the type of lens used to correct the eye defect.
List three common refractive defects of vision. Suggest the way of correcting these defects.
Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.
Name the body part with which the terms myopia and hypermetropia are connected.
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).
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 young man has to hold a book at arm's length to be able to read it clearly. The defect of vision is:
(a) astigmatism
(b) myopia
(c) presbyopia
(d) hypermetropia
To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?
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 a young man
Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.
Write whether the following is true or false:
A convex lens is used for correcting myopia.
Have a look at the posture of this woman who is reading a book and answer the questions which follow:
What are the two conditions shown in sections A and B of the eye as applicable to her?
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
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Bifocal lens
|
|
(ii) Presbyopia
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Nearsightedness
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Concave lens.
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Give Technical Term:
The type of lens used to correct myopia is
Study the following diagram carefully and then answer the questions that follow. The diagram is depicting a defect of the human eye :
(i) Identify the defect shown in the diagram.
(ii) Give two possible reasons for the above defect.
Choose the Odd One Out:
Nearsightedness : concave lens : : farsightedness : _______
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?
A person is unable to see clearly a poster fixed on a distant wall. He however sees it clearly when standing at a distance of about 2 m from the wall.
- Draw ray diagram to show the formation of image by his eye lens when he is far away from the wall.
- List two possible reasons of this defect of vision.
- Draw ray diagram to show the correction of this defect using appropriate lens.
