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Closed loop problem for lighting in thunderstorm?

  1. Jun 30, 2015 #1

    As far as I know, every circuit capable to flow current must be closed. In other word, open circuit can not flow the current, obviously. Right now, I would like to know this is also true for lighting in bad weather.

    When bottom of the dark and heavy cloud get more and more electron by convectional flow inside the cloud (positive charges are accumulated at the top of the cloud), air breakdown occurs once voltage between cloud and ground overruns breakdown voltage of the air. Then current flows from the cloud to ground. I believe majority carrier of this current is electrons from cloud.

    In circuit theory, this current must be within closed circuit. But I don't see what is closed loop in this case. It looks like current flow doesn't requires closed loop at first glancing.

    How can I overcome this apparent contradiction?
  2. jcsd
  3. Jun 30, 2015 #2


    Staff: Mentor

    Don't forget the displacement current. This is the same "current" that goes through a capacitor and was one of the key concepts in the development of Maxwell's equations. As the conduction current goes one direction, the displacement current goes the other direction, completing the closed loop.

    From a circuit standpoint you can think of lightning as closing a switch in a RC circuit where the capacitor (cloud/earth) is initially charged and the lightning is the current through the resistor.
  4. Jun 30, 2015 #3
    Oh thanks. Yes. displacement current must be included to complete the circuit. Equivalent circuit that charged cloud and earth acts as a charged capacitor and lighting as a current through resistor is just beautiful.

    Can I have one more question? Once electrons are escaping from the cloud, cloud has to be charge-neutrality again. How cloud get electrons to restore charges?
  5. Jun 30, 2015 #4


    Staff: Mentor

    That is a good question, but unfortunately, I don't know the answer to that part. Maybe some meterologist or weather enthusiast here can describe how the cloud becomes charged.
  6. Jun 30, 2015 #5


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