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Molecular speed and temperature

  1. Aug 13, 2014 #1
    Imagine a special air filter placed in a window of a house. The tiny holes in the filter allow only air molecules moving faster than a certain speed to exit the house, and allow only air molecules moving slower than that speed to enter the house from outside. What effect would this filter have on the temperature inside the house?
  2. jcsd
  3. Aug 13, 2014 #2


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    Staff: Mentor

    Google for "Maxwell's demon".
  4. Aug 14, 2014 #3
    Essentially, this filter violates the second law of thermodynamics by cooling the house and heating up the outside, even if it is already warmer outside than inside the house. This is very similar to a thought experiment known as "Maxwells Demon", as mentioned by Nugatory.

    Essentially, there is no way to construct such a filter.
  5. Aug 14, 2014 #4
    Thanks :-) both of you
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