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प्रश्न
Differentiate between myopia and hypermetropia. What type of spectacles should be worn by a person having the defects of myopia as well as hypermetropia? How does it help?
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उत्तर
| Sl. no. | Myopia (short-sightedness) |
Hypermetropia (long-sightedness) |
| 1 | A defect of vision because of which a person cannot see distant objects clearly. | A defect of vision because of which a person cannot see nearby objects clearly. |
| 2 | The far point of a myopic eye is closer than infinity. | The near point of a hypermetropic eye is more than 25 cm away. |
| 3 | Myopia occurs because the eye lens has a high converging power or because the eye ball is too long. | Hypermetropia occurs because the eye lens has a low converging power or because the eye ball is too short. |
| 4 | A person suffering from myopia should wear spectacles with concave lenses as a concave lens decreases the converging power of the eye lens and therefore helps in forming the images of faraway objects on the retina of the myopic eye. | A person suffering from hypermetropia should wear spectacles with convex lenses as a convex lens increases the converging power of the eye lens and therefore helps in forming the images of nearby objects on the retina of the hypermetropic eye. |
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संबंधित प्रश्न
In a Std. X class out of 40 students 10 students use spectacles, 2 students have positive power and 8 students have negative power of lenses in their spectacles.
Answer the following questions:
(1) What does the negative power indicate?
(2) What does the positive power indicate?
(3) Generally which type of spectacles do most of the students use?
(4) What defect of eyesight do most of the students suffer from?
(5) Give two possible reasons for the above defect.
Millions of people in the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission, how would you contribute in this noble cause?
(i) State the objective of organising such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
Name the defect of vision in which the eye-lens loses its power of accommodation due to old age.
A person suffering from the eye-defect myopia (short-sightedness) can see clearly only up to a distance of 2 metres. What is the nature and power of lens required to rectify this defect?
Though a woman can see the distant object clearly, she cannot see the nearby objects clearly. She is suffering from the defect of vision called:
(a) long-sight
(b) short-sight
(c) hind-sight
(d) mid-sight
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
The defect of vision in which the eye-lens of a person gets progressively cloudy resulting in blurred vision is called:
(a) myopia
(b) presbyopia
(c) colourblindness
(d) cataract
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?
Name the following:
The photosensitive pigment present in the rods of the retina.
Describe the mechanism of focusing the image of a distant object in your eye when you raise your head after reading a book.
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
Choose the correct answer :
Presbyopia is a disease of _____________
The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?
Give Reason:
Why do we see clearly in the central region of the retina?
What type of lens is used to correct Astigmatism?
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
Which of the following statement is correct?
Observe the figure whether it is correct or not and explain the phenomenon.
Complete the following table by observing the given figures:
| Figure → |  |
 |
| Points ↓ | ||
| (a) Name of the defect | ______ | ______ |
| (b) Position of the image | ______ | ______ |
| (c) Lens used to correct the defect | ______ | ______ |
