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प्रश्न
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?
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उत्तर
A person suffering from short-sightedness can correct the defect by wearing spectacles fitted with concave lens. In order to find the power of the concave lens, we have to first calculate its focal length.
Given, the far point of the short-sighted person is 1.5 m from the eye (the person can see the object kept at infinity if the image of the object is formed at the person's own far point of 1.5 m from the eye).
`u=oo("the distance of the object")`
`v=-1.5m("far point of the defective eye in front of thhe lens ")`
`f=? ("focal length")`
The focal length can be calculated using the lens formula `1/f=1/v-1/u`
Substituting the values in the formula, we get
`1/-1.5-1/oo=1/f`
f=-1.5m,
Since,` 1/oo=0`
Now, that we know the focal length of the concave lens, its power can be calculated.
Power `P=1/(f) ("fin metres")`
∴ `P=-1/1.5=-0.667 Dioptres ~~-0.67 "Dioptres"`
Hence, the power of the concave lens required to rectify the defect is -0.67 D.
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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.
Which defect of vision can be rectified:
by using a concave lens?
A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.
- Name the type of defect he is suffering from.
- How can this defect by corrected?
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.
Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and hot it is corrected by a lens.
The near point of a long-sighted person is 50 cm from the eye.
- Can she see clearly an object at:
- a distance of 20 cm?
- at infinity?
- To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?
Name the following:
The photosensitive pigment present in the rods of the retina.
Differentiate between members of the following pair with reference to what is asked in bracket.
Myopia and hyperopia (cause of the defect)
Choose the odd one out from the following terms and name the category to which the others belong.
Endolymph, Tympanic membrane, Semi-circular canal, Blind spot
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:
Draw a labeled diagram to show how the above mentioned defect is rectified using the lens named above.
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?
Name an old age eye defect. Why is it caused?
Differentiate between:
Myopia and Hypermetropia.
Give Technical Term:
The type of lens used to correct myopia is
In Myopia the human eye _______.
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.
