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Induction from a spark, simple question, please help!

  1. Jul 24, 2011 #1
    If I wanted to know how to find the magnetic flux through a loop, I'd need to know the current flowing near it. If that current is in the form of a spark, how do I represent that?

    The spark is nearly instantaneous, and I've got no idea how to determine the number of charges which flowed within it...

    essentially - I want to find the magnetic flux in a loop due to a spark nearby. I know that the breakdown of air is at .97MV/m... and suppose I know the length of the spark. where do I go from there? do i need more information?

    any thoughts?

  2. jcsd
  3. Jul 24, 2011 #2


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    You haven't really given us anything to go on. We would need to know the voltage between the source of the spark and whatever it is going to. (If it's just a spark in the air then just the applied voltage to the source) Is the spark just in normal air or another type of gas?
  4. Jul 24, 2011 #3
    lets say normal air with the breakdown at .97MV/m... say the spark is 2m long, that'd give us an initial V = 1.94MV
  5. Jul 24, 2011 #4


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    Alright. So how long does this spark last?
  6. Jul 24, 2011 #5
    You need two more pieces of information to solve this problem; either:
    -The energy of the spark,
    -The current of the spark,
    -Resistance of the air(at breakdown)
    time/duration of spark
    or energy

    From any of those you would solve for current. The easiest to find would probably be to find energy. For a spark plug (example) you would simply find the energy stored in any capacitors and inductors, and that would give you the energy.

    From there, realize that power is current times voltage, and that power is energy per unit time. That should get you started.
  7. Jul 24, 2011 #6
    Suppose the flash lasts for .1s...
    that gives us
    ... does this get us any further?
  8. Jul 24, 2011 #7
    You still haven't given us anything that will let us know the energy. We need the energy of the spark to do this.

    Once you have the spark energy:

    Or if you have resistance:

    Also, if you know length then Vbreakdown=kbreakdown*r

    If you have a desired current 'I' then you will have to provide P watts of power for a given spark IE:
    P=Idesired*kbreakdown*r watts

    If it's a short duration spark, then time will be determined by input Energy and resistivity of ionized air.
    Last edited: Jul 24, 2011
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