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What is presbyopia ? Write two causes of...

What is presbyopia ? Write two causes of this defect.

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Presbyopia is a defect of vision where a person can see distant objects clearly but nearby objects appear blurry. This defect arises in aged persons due to causes.
(i) ciliary muscles gradually become weak, and
(ii) eye lens hardens and its flexibility diminishes with ageing. Because of these reasons, eye loses its power of accomodation and its near point gradually recedes. So, nearby objects cannot be focussed on the eye lens clearly.
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ZEN PUBLICATION-THE HUMAN EYE AND THE COLOURFUL WORLD-ZEN ADDITIONAL QUESTIONS SECTION - SHORT ANSWER TYPE QUESTIONS - I
  1. Name the part of eye where the image is formed in a nornaml human eye....

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  2. What is hypermetropia or far-sightedness ? Name the type of lens used ...

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  3. What is presbyopia ? Write two causes of this defect.

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  4. What are bifocal lenses ? Who needs to use them ?

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  5. A person is able to see objects clearly only when these are lying at a...

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  6. What is dispersion ? What happens when light is passed through a glass...

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  7. A beam of white light falling a glass prism split up into seven colour...

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  8. List the three phenomena of light responsible for the formation of rai...

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  9. A beam of light consisting of red, blue, and yellow colours is inciden...

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  10. When a beam of white light is passed through a triangular glass prism,...

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  11. Name the phenomenon responsible for (i) advance of sunrise (ii) colour...

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  12. A star sometimes brighter and at other times fainter. What is this eff...

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  13. Why do we see a rainbow in the ske only after rainfall ?

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  14. Mention any four phenomena that can be observed due to atmospheric ref...

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  15. What is the difference in colours of the sun observed during sunrise/s...

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  16. Sun appears red in colour during sunrise but appears white at noon. Ex...

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  17. Why does the sun seem to rise two minutes before the actual sunrise an...

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  18. The sun near the horizon appears flattened at sunset and sunrise. Expl...

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  19. Is the position of a star as seen by us its true position ? Justify yo...

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  20. "Stars appear higher than they actually are". Give reason.

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