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I Lightning movement

  1. Apr 25, 2017 #1

    I need to know a bit about lightning/discharge, in a small scale ofcourse.
    I have the impression that we can somehow (with a battery) charge a metallic tip and then if we put another metallic tip close enough, a lightning will be created. Is this correct?

    In addition, I would like to know, is it possible to have a disk with several metallic tips on its surface and when approaching that to a charged metallic tip, lightning will be created across all the metallic tips of the disc? In other words, is it possible to make the lightning travel from one tip next to the other? How?

  2. jcsd
  3. Apr 25, 2017 #2


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    Yes, like the spark plug in your car.
  4. Apr 25, 2017 #3


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    The only problem is that you need a voltage between the two discs that is dangerously high. To get a spark to form, you have to ionise the air in between. That involves producing free electrons which can carry the current, which requires several thousand volts and a spark plug gap is only around 1mm wide. There are ways to make this happen more safely and the Plasma Balls you can buy in Novelty / Science shops produce safe versions of lightning strikes by using gas at low pressure and a high frequency to cause the sparks to flow. These sparks are essentially just like lightning strikes. A very similar thing happens in fluorescent light tubes but they don't look as impressive - they are designed to produce light instead and the 'spark' travels down the inside of the tube and all you see is the glow of the phosphor coating round the outside.
    Unfortunately, we can't really recommend home experimenting, even with models of lightning. :smile:
  5. Apr 25, 2017 #4


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  6. Apr 25, 2017 #5
    very interesting finding!
    but how does it work? how does it relate to my (2nd) question exactly?
  7. Apr 25, 2017 #6
    An electrical discharge (lightning), happens when there is a large difference in charge between one object and another.
    A lot of different tips on one object will not vary much in electrical potential.
    No discharge
  8. Apr 26, 2017 #7


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    It's the Field that counts, here - i.e. the separation between those two charges needs to be small or they won't talk to each other, whatever the value of the charges.
  9. Apr 26, 2017 #8


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    @physea :

    (1) It is a Marconi radio transmitter which uses high energy sparks to generate the radio waves .

    The rotating disc has a ring of electrode points on it and the spark from the two fixed electrodes jumps to each point on the disk in turn as the disk revolves .

    (2) An inverse of that could be a conical pendulum with an electrode point on the end rotating above a ring of fixed electrode points .

    (3) High energy sparks do not always follow the simple rules about conduction paths . If you ever have the opportunity visit the Deutsches Museum in Munich and see the high voltage discharge laboratory demonstrations . You will see sparks there doing some quite amazing things .
    Last edited: Apr 26, 2017
  10. May 18, 2017 #9
    that's not true, lightning (weather phenomenon) happens with many meters distance

    also, see 2:40 of this
  11. May 18, 2017 #10


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    Misunderstanding here. I should have written "small enough" to make it clearer. I still say that it is the Field (=volts per meter) that causes ionisation (in the absence of other ionising particles or radiation) An added detail is that it is the local field that I am talking about. The local field around a sharp point is much higher than in the gap in between so you can say that the volts are shared unequally (as in volts per meter) across a gap.
    B ut my point was that the displaced charge can be anything from hundreds of coulombs (across the plates of a large Capacitor) to milliCoulombs, as on the ball of a Van Der Graaf generator. The volts can be the same and the arc will strike - all other things being equal.
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