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A myopic person has been using spectacle...

A myopic person has been using spectacles of power -1.0 dioptre for distance vision. During old age he also needs to use separate reading glass of power +2.0 dioptres. Explain what may have happened.

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The far point of the person is 100 cm, While his point may have been normal (about 25 cm ). Objects at infinity produce virtual image at 100 cm (using spectacles ). To view closer objects i.e., those which are (or whose images using the spectacles are ) between 100 cm and 25 cm, the person uses the ability of accommodation of his eye-lens. This ability usually gets partially lost in old age (presbyopia). the near point of the person recedes to 50 cm . To view objects at 25 cm clearly. the person needs converging lens of power + 2 dioptres.
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NEW JOYTHI PUBLICATION-RAY OPTICS AND OPTICAL INSTRUMENTS -SOLUTIONS TO EXERCISES FROM NCERT TEXT
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  2. For a normal eye, the far point is at infinity and the near point of d...

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  3. A myopic person has been using spectacles of power -1.0 dioptre for di...

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  4. A person looking at a person wearing a shirt with a pattern comprising...

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  5. A man with normal near point (25 cm ) reads a book with small print us...

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  6. A card sheet divided into squares each of size 1 mm^(3) viewed at a ...

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  7. a. At what distance should the lens be held in Exercise 27 in order t...

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  8. If the object is at (50/7)cm and the image produced is at distinct vis...

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  9. Is the magnification equal to the magnifying power in this case ? Expl...

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  10. What should be the distance between the object in Exercise 28 and the ...

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  11. The angle subtended at the eye by an object is equal to the angle subt...

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  12. In viewing through a magnifying glass, one usually positions one's eye...

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  13. Magnifying power of a simple microscope is inversely proportional to t...

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  14. Why must both the objective and the eyepiece of a compound microscope...

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  15. When viewing through a compound microscope, our eyes should be positio...

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  16. An angular magnification (magnifying power ) of 30x is desired using o...

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  17. A small telescope has an objective lens of focal length 140 cm and eye...

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  18. For the telescope described in Exercise 32 (a ) , whet is the separati...

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  19. Focal length of the Objective lens is 140 cm. Focal length of the eyep...

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  20. A height of a tower formed by a objective lens of a telescope is 4.7 c...

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