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My chemistry teacher/book states that lightning is just light, and therefore has no mass and takes up no space (we're not very far through the book yet, it's defining matter).

However, I take issue with this statement - it feels wrong. My reasoning is this: Lightning, as far as I know, is simply electrical energy. Also, I believe that electrical energy needs a medium to travel through, right?

If this is true, wouldn't the air the lightning travels through be the mass and space the lightning takes up?

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up vote 6 down vote accepted

Lightning is not 'just light', it is according to this NOAA National Severe Storms Laboratory FAQ,

Lightning, as best we understand, is a channel of electrical charge, called a stepped leader that zigzags downward

So, technically speaking, the mass of a lightning bolt could be the sum of all the electrons and the plasma within the electrical charge channel. (thank you to tpg2114)

Each electron has a mass of about $9.11 × 10^{-31}$ kilograms, but it would not really be feasible to exactly count how many electrons there are in a single lightning bolt, hence, not feasible to get an exact mass.

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The light itself is caused by an electrical charge which creates a plasma in the air through which it travels. So I would say that if you wanted to "weigh" a lightning bolt, you would have to take the weight of the plasma, not just the electrons. –  tpg2114 Sep 23 '13 at 14:57
    
@tpg2114 yes, that is why I said lightning is not just light (as the OP's teacher claims) –  user29350 Sep 23 '13 at 14:59
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Sure, but you claim So, technically speaking, the mass of a lightning bolt would be the sum of all the electrons within the electrical charge channel. which I disagree with. It should be the weight of the plasma, which is not just the electrons. –  tpg2114 Sep 23 '13 at 15:01
    
Of course, if you don't agree with my disagreement, you can leave your answer as is and I can post my own when I get some time :) –  tpg2114 Sep 23 '13 at 15:01
    
@tpg2114 I agree with you, just had not had the chance to edit until now...thank you for the additional insight. –  user29350 Sep 23 '13 at 15:04
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It depends on how you define "lightning". When electrons flow from clouds to the earth, ionizing the air and producing light, does your definition include the electrons, the air, the plasma, the light, or a subset?

Pedantically speaking, I would say that lightning is the flow of electrons, and to me a flow is an abstract idea (the action of moving in a steady, continuous stream) instead of a concrete object with a mass.

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