Is lightning caused by the cloud acting as a capacitor?

  1. So I was looking up what causes thunderstorms online and found this:
    "As hail moves within the cloud it picks up a negative charge by rubbing against smaller positively charged ice crystals. A negative charge forms at the base of the cloud where the hail collects, while the lighter ice crystals remain near the top of the cloud and create a positive charge.

    The negative charge is attracted to the Earth's surface and other clouds and objects and when the attraction becomes too strong, the positive and negative charges come together, or discharge, to balance the difference in a flash of lightning (sometimes known as a lightning strike or lightning bolt). The rapid expansion and heating of air caused by lightning produces the accompanying loud clap of thunder."

    The line that really interested me was this: "and when the attraction becomes too strong, the positive and negative charges come together". This sounds to me like a capacitor.

    Am I correct in thinking this or am I mistaken?
  2. jcsd
  3. mfb

    Staff: Mentor

    Well, you have separated charges with a bad conductor (air) in between, that is similar to a capacitor.
  4. (i think) you have thought a correct analogy between lighting and capacitance . What i think is that when lighting strikes them the maximum capacitance of air is crossed and the charge is finally transferred from clouds to the land .
  5. Baluncore

    Baluncore 3,305
    Science Advisor

    You have described the currently accepted paradigm correctly. Unfortunately it does not explain everything that is observed and so will be subject to revision at some time in the future.

    When the potential difference between two parcels or pools of opposite charge exceeds the breakdown voltage of the air, an ionised path called lightning forms that discharges the local charge difference.

    There is capacitance between the two parcels of air and there is a charge difference. The voltage is therefore V = Q / C, derived from the definition of capacitance C = Q / V.
  6. To answer the question you posed in the title, whether capacitance "causes" lightning is a matter of semantics.
    Without the capacitance, there would still be a discharge, but it would have to be a continuous current. It would not be lightning-like.
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