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Backstory: I’m a software engineer just getting into electronics and it seems that everything I’ve ever been told about electricity my whole life is a candy-coated lie. I can’t find consistent logical answers to the most basic of questions and it’s driving me mad!

I’m old enough now. I just want to know the truth, even if it hurts.

This is a follow-up to How does resistance *really* work? (DC, battery, LED, atoms, electrons)

The math

A volt is electric potential energy per unit charge

J = CV

V = J/C

Thus “volt” is NOT a unit of charge, as we’ve been told in school - because that’s what a Coulomb is.

However, how does one store a Joule in a Coulomb? My best guess is that it has something to do with the energy levels of the electrons in the atom.

If it’s merely a product of the charge creating an electric field, that makes sense too... it just seems a little tautological - which is maybe okay.

All of this is assuming that the math is correct and not just another candy-coated fairy tale.

The effect of charge on voltage

Here’s a hypothesis I have. Please tear it apart.

  1. A balloon and I are perfectly zero charge.
  2. The balloon is an insulator.
  3. My hair is an insulator.
  4. My body is “ground” (endless electron supply)
  5. I rub my head on a balloon.
  6. The rubbing causes the atoms to energize.
  7. The energy causes some electrons to “level up” to the next shell.

Pause.

Does this energy alone create voltage?

(I’m assuming there’s no charge yet because no hypothetical electrons have left their own atoms)

  1. The most excited electrons “jump ship”.

Are they going to the balloon or to my hair?

I’m assuming they must be drawing from my body and going to the balloon,

  1. The balloon is now “positively” charged (Ben Franklin style) with excess negative electrons (real physics style)

  2. The balloon repels the electrons in my hair, which escape to my body (with great difficulty), during the high-energy rubbing.

  3. My hair is now “negatively” charged (with all those positive holes).

  4. Without the excess energy, the excess electrons (that left to my body) can’t flow back through my hair.

  5. My hair is charged and has -2500 volts between it and neutral things.

  6. The balloon is charged and has +2500 volts between it and neutral things.

  7. There’s now +5000 volts between the balloon and my hair (or -5000 between my hair and the balloon).

  8. Attraction happens and, because the very small amount of current can’t flow, I hear a lightning crack between the balloon and my hair, restoring the balance of the force in true arcing Jedi fashion.

This seems to make sense... but is it true? What's really happening?

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  • $\begingroup$ important note: what you are describing is static electricity, which lives on the surfaces of electrically insulating materials and which can be transferred from one surface to another by rubbing. this is very different from the movement of electrical currents through conductors, and this difference may be the source of your confusion on this topic. we can discuss further... -NN $\endgroup$ – niels nielsen Jan 19 at 7:24
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6 The rubbing causes the atoms to energize.

Not quite. Somehow (and this isn't well modeled), the physical action of the materials pulls electrons off some of the atoms. As the material is moved away (still holding the electrons), the charges are separated.

7 The energy causes some electrons to “level up” to the next shell.

Not really. The energy is stored in the charge separation, not in energized atoms.

I’m assuming they must be drawing from my body and going to the balloon,

Correct here. The rubbing action moves electrons from your hair to the balloon, making it negatively charged.

8 The balloon is now “positively” charged (Ben Franklin style) with excess negative electrons (real physics style)

The balloon is negatively charged either way you look at it. Ben would have said the balloon passed a (positively) charged electrical fluid to the hair. But now we know the charge carriers are negative, so it really moves the other direction.

9 The balloon repels the electrons in my hair, which escape to my body (with great difficulty), during the high-energy rubbing.

No. The rubbing pushes electrons onto the balloon. Since it's a pretty good insulator, they just hang out there and don't really move around much. Your body might have a slight electron deficit, but not much.

10 My hair is now “negatively” charged (with all those positive holes).

Your hair is now (slightly) positively charged because of the electrons that left.

11 Without the excess energy, the excess electrons (that left to my body) can’t flow back through my hair.

No, they can't flow back because they're on an insulator, and it's very difficult for electrons to move across one. If they were all on a metal rod instead, they'd move off into your body rapidly.

12 My hair is charged and has -2500 volts between it and neutral things. 13 The balloon is charged and has +2500 volts between it and neutral things.

The negatively charged balloon would have a negative voltage, not a positive one. But we can assume that these values could be generated.

Attraction happens and, because the very small amount of current can’t flow, I hear a lightning crack between the balloon and my hair, restoring the balance of the force in true arcing Jedi fashion.

"current can't flow". If charge is flowing, it's a current. If charge isn't flowing, there's no current.

Because it's a good insulator, rather than a big "crack", you'll probably hear lots of tiny crackles as you bring the back of your hand or something near the balloon. As your skin gets near enough, the voltage between two bits is enough for them to jump through the air (a spark). But many of the neighboring patches remain charged until something comes close enough to repeat the process there.

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When you do something that moves an electron up or down an orbital (like hit the right material with a photon or perform a chemical reaction), the movement is so small relative to other molecules that the charge appears to not have moved.

When you rub two materials like your hair and the balloon together, you are using the Triboelectric Effect to actually transfer electrons from one object to the other.

As you transfer more charge or move the two objects closer together, eventually the force on the electrons due to the voltage is enough to move electrons from one object to the other. Incidentally, when this starts to happen, the air with extra electrons becomes ionized and its resistance drops, hence BANG! Jedi magic...well, a sudden spark.

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