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(a) What is long-sightedness ? State the...

(a) What is long-sightedness ? State the two causes of long-sightedness (or hypermetropia). With the help of ray diagrams, show :
(i) the ray-defect long-sightedness.
(ii) correction of long-sightedness by using a lens.
(b) What 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 ?
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 ?

Text Solution

Verified by Experts

The correct Answer is:
(b) Convex lenses ; + 2.67 D ; Long-sighted (c) Concave lenses ; - 0.5 D ; Short-sighted
NA
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(a) What is short-sightedness ? State the two causes of short-sightedness (or myopia). With the help of ray diagram, show : (i) the eye-defect short-sightedness. (ii) correction of short-sightedness by using a lens. (b) 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 ?

(a) What is myopia? State the two causes of myopia. With the help of labelled ray diagrams show (i) the eye defect myopia (ii) correction of myopia using a lens. (b) Why is the normal eye unable to focus on an object placed within 10 cm from the eye?

Knowledge Check

  • Long-sightedness is caused due to

    A
    eye ball being too short.
    B
    eye ball being too long.
    C
    the blind spot on the retina.
    D
    None of the above.

  • Long-sightedness is caused due to

    A
    eye ball being too short.
    B
    eye ball being too long.
    C
    the blind spot on the retina.
    D
    None of the above.

  • Long-sightedness is to hypermetropia as short-sightedness is to

    A
    myopia
    B
    focusing
    C
    astigmatism
    D
    accommodation

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    Short-sightedness can be corrected by

    In myopia or short sightedness

    A far sighted person has a near point of 60 cm. What power lens should be used for eye glasses such that the person can read a book at a distance of 25 cm.

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