(a) What is short-sightedness ? State the two causes of short-sightedness (or myopia). With the help of ray diagrams, 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 ?

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Solution

a) Short Sightedness is that defect of vision due to which a person can see nearby objects clearly but cannot see distant objects clearly.
Causes:
1. Excessive curvature of the eye lens
2. Elongation of the eyeball
Ray diagram for:
(i) eye-defect short sightedness

(ii) Correction of short-sightedness by using a lens

(b) Concave lens should be used to restore proper vision
calculated power:
$h e r e comma space f a r space p o i n t space o f space m y o p i c space e y e space equals space 1.5 m T h e space o b j e c t space space k e p t space a t space i n f i n i t y space c a n space b e space s e e n space c l e a r l y space i f space t h e space i m a g e space o f space t h i s space o b j e c t space i s space f o r m e d space a t space 1.5 m I m a g e space d i s tan c e comma space v space equals space 1.5 m 1 over v minus 1 over u equals 1 over f fraction numerator 1 over denominator negative 1.5 space end fraction minus 1 over infinity space equals 1 over f f space equals space minus 1.5 m P space equals space 1 over f equals space fraction numerator 1 over denominator negative 1.5 end fraction space equals space minus 0.67 D$

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Similar questions

(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. Complete the following sentences :
(a) A short-sighted person cannot see .............. objects clearly. Short-sightedness can be corrected by using ............... lenses.
(b) A long-sighted person cannot see ............... objects clearly. Long-sightedness can be corrected by using .............. lenses.

Q. A person suffering from myopia (short-sightedness) can see clearly only up to a distance of 2m.What is the power of concave lens required to rectify this defect?

Q. What is myopia (or short sightedness)? What is the cause of this defect? How can this defect be minimized? Explain drawing a ray diagram.

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