The near point of a long sighted person is 40 cm from the eye. To read a book held at a distance of 25 cm, he will need spectacles containing

Chromatic lenses

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Prismatic lenses

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Concave lenses

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Convex lenses

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Solution

The correct option is D Convex lenses
$A n s w e r : -$ D option
Long sightedness means converging power of eye lens has decreased so to increase converging power converging lens or convex lens is needed.
By using convex lens we are focussing image to be formed at retina ,earlier due to long sightedness near point was shifted to 40 cm but by using convex lens it is now shifted to 25cm

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Similar questions

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 ?
(b) To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses ?

Q. A long-sighted person cannot see objects clearly at a distance less than

40 c m

from his eye. The power of the lens needed to read an object at

25 c m

(a) What is long-sightedness ? State the two causes of long-sightedness (or hypermetropia). With the help of ray diagrams, show :
(i) the eye-defect long-sightedness.
(ii) correction of long-sightedness by using a lens.
(b) An eye has a near point distance of 0.75 m. What short 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 ?
(c) An eye has a far point of 2 m. What type of lens in spectacles would be needed to increase the far point to infinity ? Also calculate the power of lens required. Is this eye long-sighted or short-sighted ?

Q. What is long-sightedness? The near point of a long-sighted person is at

100 c m

from his eyes. What would be the power of the lens to be used by him in order to read a book placed at

25 c m

from his eyes?

Q. A person has near point at

100 cm

. What power of lens is needed to read at

20 cm .

If he/she uses spectacles, having glasses

2 cm

separated from eyes?

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