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प्रश्न
Observe the figure and answer the following questions:
- Name the defect of vision represented in the above figure.
- State the reasons for this defect.
- How is it corrected?
- Draw the diagram to show the correction of this defect.
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उत्तर
- In the figure, Myopia or Nearsightedness defect of vision is represented.
- There are two reasons for this defect.
1. The curvature of the cornea and the eye lens increases. The muscles near the lens can not relax so the converging power of the lens remains large.
2. The eyeball elongates so that the distance between the lens and the retina increases. - This defect can be corrected by using spectacles with concave lenses of proper focal length. This lens diverges the incident rays and these diverged rays can be converged by the lens in the eye to form the image on the retina. The focal length of the concave lens is negative, so a lens with negative power is required for correcting nearsightedness. The power of the lens is different for different eyes depending on the magnitude of their nearsightedness.
Correction of Nearsightedness
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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.
List three common refractive defects of vision. Suggest the way of correcting these defects.
the biological/technical terms for the lens of eye losing flexibility resulting in a kind of long-sightedness in middle aged people.
Which defect of vision can be rectified:
by using a concave lens?
Which defect of vision can be rectified:
by using a convex lens?
What is the other name for
myopia
What is the other name for
hypermetropia
What is the scientific name of
long-sightedness?
Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.
A man can read the number of a distant but clearly but he finds difficulty in reading a book.
From which defect of the eye is he suffering?
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.
Explain with the help of labelled ray diagram, the defect of vision called myopia and how it is corrected by a lens.
Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and hot it is corrected by a lens.
A person having short-sight cannot see objects clearly beyond a distance of 1.5 m. What would be the nature and power of the corrective lens to restore proper vision?
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 person cannot see the distant objects clearly (though he can see the nearby objects clearly). He is suffering from the defect of vision called:
(a) cataract
(b) hypermetropia
(c) myopia
(d) presbyopia
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
Name the following:
The photosensitive pigment present in the rods of the retina.
What is meant by optical illusion? Give one example.
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
Have a look at the posture of this girl who is reading a book and answer the questions which follow:
Name the problem she is facing.
An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also (ii) for its correction.
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
Draw a ray diagram to show how Hypermetropia is defect can be corrected using a lens.
List two causes of presbyopia. Draw labelled diagram of a lens used for the correction of this defect of vision.
Write whether the following is true or false:
A convex lens is used for correcting myopia.
Choose the correct answer :
Presbyopia is a disease of _____________
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow :
Name the type of lens used to correct this eye defect.
Give Reason:
Deficiency of vitamin A causes night blindness.
Give Reason:
When you enter into a dark room from bright because of sunlight, you can not see things for a few seconds.
Give Technical Term:
The type of lens used to correct myopia is
Choose the Odd One Out:
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
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?
Have a look at the posture of this girl who is reading a book and answer the questions which follow:
 |
- Name the problem she is facing.
- What are the two conditions shown in sections A and B of the eye as applicable to her.
- What kind of reading glasses does she need?
 |
 |
| A | B |
