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What are bifocal lenses ? Who needs to u...

What are bifocal lenses ? Who needs to use them ?

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Bifocal lenses are eyeglasses made of two distinct lenses-an upper convex lens and a power concave lens- attached suitably. It is used by people suffering from a visual defect where they cannot see nearby and distant objects clearly. The concave lens is used for to aid distant vision while convex lens helps viewing nearby objects clearly.
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ZEN PUBLICATION-THE HUMAN EYE AND THE COLOURFUL WORLD-ZEN ADDITIONAL QUESTIONS SECTION - SHORT ANSWER TYPE QUESTIONS - I
  1. What is hypermetropia or far-sightedness ? Name the type of lens used ...

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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  20. Explain how the colour of the scattered light depends on the size of t...

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