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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?
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उत्तर
The person is suffering from an eye defect called myopia. In this defect, the image is formed in front of the retina. Hence, a concave lens is used to correct this defect of vision.
Object distance, u = infinity = ∞
Image distance, v = – 80 cm
Focal length = f
According to the lens formula,
`1/"v" - 1/"u" = 1/"f"`
`1/(-80) - 1/(-∞) = 1/"f"`
`1/(-80) = 1/"f"`
f = −80 cm = −0.80 m ...(concave lens)
∴ power of modified lens,
P = `1/"f"`
= `1/(-0.80 "m")`
= −1.25 D
A concave lens of power −1.25 D is required by the person to correct his defect.
संबंधित प्रश्न
What is the far point and near point of the human eye with normal vision?
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
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?
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?
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
Name the following:
The photosensitive pigment present in the rods of the retina.
Name the following:
The eye defect caused due to shortening of the eye ball from front to back.
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
Draw a ray diagram to show how Hypermetropia is defect can be corrected using a lens.
Distinguish between the following pair of words:
Myopia and hypermetropia
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?
Draw a neat labeled diagram to show how hypermetropia can be rectified.
Name the following:
The defect of the human eye caused due to the uneven surface of the cornea.
Give Technical Term:
The type of lens used to correct myopia is
In Myopia the human eye _______.
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
Assertion: Myopia is the defect of vision in which a person cannot see distant objects clearly.
Reason: This due to eye-ball being too short.
Which of the following statement is correct?
Match the following:
| Column - I | Column - II |
| 1. Retina | a. Path way of light |
| 2. Pupil | b. Far point comes closer |
| 3. Ciliary muscles | c. near point moves away |
| 4. Myopia | d. Screen of the eye |
| 5. Hypermetropia | e. Power of accommodation |
Given alongside is a diagram depicting a defect of the human eye. Study the same and answer the questions that follow:
 |
- Name the defect shown in the diagram.
- Give two possible reasons for this defect.
- Name the parts labelled 1 to 4.
- Name the type of lens used to correct this eye defect.
- Draw a labelled diagram to show how the above mentioned defect is rectified using the lens named above.
