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2 questions

  1. Feb 2, 2007 #1
    1.If the tube of a faulty barometer is pushed down into the mercury trough, the barometric height will further decrease. Why does this happen?

    2. If I am provided with two similar bars, one is a magnet and the other is soft iron. How can I distinguish between them with out using any other thing?
  2. jcsd
  3. Feb 2, 2007 #2


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    Show some work- we cannot help you until you first attempt the problem
  4. Feb 3, 2007 #3
    I think that when tube is lowered, mercury should rise up. But this doesnt happen.

    If I suspend both the rods, both will come to rest in North-South direction so I cannot think of any other way except cuttin the 2 rods into four and then testing them.
  5. Feb 5, 2007 #4
    I'm still working on the first question. Meanwhile the second is easier.

    Take one of the bars and place its one end at about the middle of the length of the other bar (so that they look perpendicular to each other). If there's a strong attraction b/w the two bars at this position it means that the bar you're holding in your hand is the magnet. If the attraction is weak then you're holding the iron bar.

    Principle: Magnetic field due to a magnet is weak at the center.
  6. Feb 5, 2007 #5
  7. Feb 5, 2007 #6


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  8. Feb 6, 2007 #7
    It is not mentioned in the question what the fault is. Does it imply that air is trapped in place of vacuum?
  9. Feb 6, 2007 #8
    Yes. Thats exactly the case!!
  10. Feb 6, 2007 #9
    Well, then here's my explanation (although I'm not entirely sure):

    For a capillary tube dipped in mercury, a depression in mercury level is observed inside the tube. Here air is the medium above the surface in the tube as well as the vessel. For the faulty barometer a somewhat similar condition must be happening because there is some air trapped inside. But clearly the barometer tube is no capillary tube and that's why I'm doubtful on this explanation.
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