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प्रश्न
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).
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उत्तर
A person suffering from hypermetropia can correct the defect by wearing spectacles with convex lenses. In order to find the power of the convex lens required, we have to first calculate its focal length.
Given that the near point of the hypermetropic eye is 50 cm in front of the eye (the person can see an object kept at the normal near point of 25 cm from the eye if the image of the object is formed at the person's own near point of 50 cm from the eye).
u = -25 cm (the distance of the object at the normal near point)
v = -50 cm (the location of the near point of the defective eye)
f = ? (focal length)
The focal length can be calculated using the lens formula `1/v-1/u=1/f`
Substituting the values in the formula, we get `1/50-1/-25=1/f`
`1/-50+1/25=1/f`
`((-1+2))/50=1/50=1/f`
∴f=50cm=0.5cm
Now that we know the focal length of the convex lens, the power can be calculated.
Power P=`1/f(termertrs)`
∴` P=1/0.5=+diopters`
Hence, the power of the convex lens required to rectify this defect is +2 dioptres.
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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.
Name the defect of vision in a person:
whose near point is more than 25 on away.
What is the scientific name of
short-sightedness
Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.
A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.
How can this defect by corrected?
What is Hypermetropia (far sightedness)?
Select the odd one in the following series:
Endolymph, Tympanic membrane, Semi-circular canal, Blind spot.
Distinguish between the following pair of words:
Myopia and hypermetropia
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.
Name the common defects of the eye.
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.
Explain the Term: Cataract
Give Technical Term:
The type of lens used to correct myopia is
Due to elongation of _______ and increase in curvature of the eye lens, a person cannot see distant objects clearly.
Nearsightedness : concave lens : : farsightedness : _______
Myopia and hypermetropia can be corrected by:
Myopia may arise due to ____________.
Which of the following statement is correct?
Draw ray diagram showing myopic eye.
