Sunday, November 13, 2011

Does Radioactive Decay Cause Lightning?

Next week I am supposed to teach a unit of Grade 9 Science: static electricity. I am going crazy trying to make those damned experiments work! You rub this or that with a piece of fur and little pieces of paper are supposed to jump up and down: but try and explain it? Oh, I know, it’s all very simple: there is the triboelectric effect, and there is induced charge, but do you think it actually works the way the lab manual says it does? Try it yourself.

I can hardly begin to count the number of contradictions I find when I actually try to resolve the theory with what I am actually seeingin my basement. Actually, I’m exaggerating: I can resolve quite a few of them,but when I step into the classroom tomorrow I’m supposed to explain this stuffat the Grade 9 level: no Coulombs law, no concept of voltage or capacitance,nothing but “like repels like” and “electricity is made of particles”. It’s a scary prospect.

I’m not going to get into detail today on the experiments, but there is one glaring fact that everybody knows. It’s a lot easier to put a negative charge on something than a positive charge. Why is this?? When I rub a balloon with a piece of wool, doesn’t the wool get just as much positivie charge as the balloon gets a negative charge? But if I walk over to the wall, I can stick the balloon on the wall and it stays right there. If I put the piece of wool on the wall, it just falls down. Yes, I know, the wool is heavier than the balloon. But I have not been able over the last three days of effort to find one indication that there is positive charge on the wool. What am I doing wrong?

I came up with a theory that the air is actually full with a surplus of negative charges. So when you put a negative charge on the balloon, it stays there because the negative air charges are repelled. But the positive charge on the wool is rapidly neutralized by the ambient negative charge.

This sounded OK, but then I read about lighting on the internet. It seems that there is no real theory of how lightning works! There are bits and pieces of a theory, but it just doesn’t all add up. And the first thing that doesn’t make sense is that on some level, the whole planet seems to have a negative charge and the atomsphere is positively charged. So the potential rises as you gain altitude, at a rate of about 100 volts per meter. This trashes my theory of negative charge.

But it got me thinking about lightning, and I asked my self the question: could the charge of the planet be caused by radioactive decay? Alpha particles carry a positive charge and they are being given off by uranium atoms. How many of them make it out of the earth’s crust unscathed to the atmosphere? Are they enough to account for the quantity of atmospheric electricity?

From Wikipedia I got a ballpark figure of 10^20 grams of uranium in the top 25 km of the earth’s crust. This is on the order of 10^18 moles. Since there are 10^5 coulombs in a mole, it is 10^23 coulombs of available electricity. These atoms are decaying at a rate of one decay per atom per four billion years. I ran the figures and it comes to about one million amperes.

Some of these alpha particles will be neutralized before they escape the earth’s crust. But how many? Also from Wikipedia, I learn that there are, worldwide, about 50 lightning strikes per second, each delivering an average of 15 coulombs. In other words, planetary lightning represents an average current of about 1000 amps.

It seems that if less than 1% of the alpha particles generated by uranium decay actually make it into the atmosphere, it would be enough to explain lightning. I guess that’s my theory for today. I recently wrote about how I got ripped off for the Nobel Prize because I was just 78 years late in explaing the Compton Effect by the wave theory of light. Well, maybe I’ll have more luck with this theory.

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