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Helium vs Air Plasma

  1. Aug 23, 2014 #1
    After a science fair experiment we have measured the similarities and differences of plasma created by air and helium. Our methodology is as follows.
    Methodology A(air):
    1. Light a match and place it on a small raised surface inside a microwave
    2. Cover the match with a glass bowl/beaker, leaving a slight gap so air can ventilate the match.
    3. Close the microwave door and turn it on for 15-20 seconds
    4. Place electromagnet directly outside the microwave door
    microwave door

    Methodology B(helium):
    1. Light a match and place it on a small raised surface inside a microwave
    2. Fill a glass bowl/beaker with Helium, upside down so it doesn’t escape (because helium is lighter than air).
    3. Cover the match with the bowl/beaker, leaving a slight gap so air can ventilate the match.
    4. Close the microwave door and turn it on for 15-20 seconds
    5. Place electromagnet directly outside the microwave door


    The helium reacted differently in the following ways: The helium plasma only took 2 seconds to ionize, whereas the air plasma took 3. Also the colour was slightly different in the two experiments. Perhaps the biggest difference was how when the electromagnet was introduced the air plasma took the shape of a small ball near the top of the beaker, while the helium plasma shook violently and eventually turned into an ionized flame. I was wondering why this happened and the science behind it.
    Thanks in advance; Harry
     
  2. jcsd
  3. Aug 23, 2014 #2

    Simon Bridge

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  4. Aug 25, 2014 #3

    Simon Bridge

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    This is a domestic microwave oven right?
    With a turntable?

    Something like this:


    How many repeats of each experiment did you do?
    Did you do the experiment without switching the microwave on?
    Did you do the experiment without lighting the match, but the microwave is on?
    (i.e. what is the role of each part of the experiment?)

    I take it the match went out during the experiment - did you wait for the match to go out before turning the microwave on?

    Note: in one you have a mix of air and helium, in the other you just have air.
    After the match is lit, you can add the burning products from the match - these include carbon, sulfur, and phosphor compounds.

    You have vibrations from the oven machinery, and uneven air-flow into and out of the container.

    So there are quite a lot of variables to consider.

    The main difference you observed concerned the stability of the glow - which will be due to the different mass and thermal properties of the gasses.

    Note: microwave ovens do not have enough energy to ionize helium to a plasma.
    From what I gather, it is unlikely that the glow you see is from a plasma and more likely from normal hot gas - maybe the phosphor from the match is florescing? Need to check some more.
    http://hyperphysics.phy-astr.gsu.edu/hbase/waves/mwoven.html
     
    Last edited by a moderator: Sep 25, 2014
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