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I am not a expert on physics, just another high schooler, so sorry if the question is obvious.

This is something I've been wondering about for a while. Why is the charge on a proton equal but opposite to the charge on the electron? A proton is much larger than a electron, and apparently a lot more heavier too. Why, then, is it's charge equal to that on a electron? Just what is charge, and what defines it? What factors decide the charge on a particle?

Also while we're at it, why does the atom in it's default configuration have the same number of protons and electrons? Edit: To expand on this a bit, from what I know the attraction weakens as distance increases. So if theoretically a huge amount of protons were to be somehow brought together despite the repulsions constantly increasing, would a atom with a extremely high atomic number defy the proton = electron rule?

Note: This is not a duplicate. I read through the Phys.SE post Why do electron and proton have the same but opposite electric charge? but I did not find a satisfactory answer (Or even understand many of the professional terms :s)

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Aayush Agrawal
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  • This question is too broad. You ask what is electric charge (Coulomb's law, U(1) symmetry...), why do electrons and protons have the same charge, why do particles have a particular charge (there is not theory which predicts why) , why is the atom neutral... Minor note:A proton is much larger than a electron No, they are both size 0. – jinawee Jan 27 '14 at 16:00
  • @jinawee: cough form factor cough – Christoph Jan 27 '14 at 16:13
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    It is a duplicate. Your not liking the answer already given does not change the fact that they are answer to your question, and we don't need to have the answer scattered over even more questions: they should all be in one place. – dmckee --- ex-moderator kitten Jan 27 '14 at 16:14
  • @dmckee: note that it's only half a duplicate as it contains two separate questions – Christoph Jan 27 '14 at 16:40

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Because we all exist!Because this question can be typed without extreme strains!

Suppose on the other hand they were not equal and differed say even by a part in a billion.Then our body which approximately has $\approx 10^{28}$ atoms.Even considering the feeble charges on individual electrons and protons($e=1.6 \times 10^{-19} C$),a difference in one part in a billion will cause our body to have a charge of magnitude of $\approx e \times 10^{28} \times 10^{-9}=1 C$.That's a lot of charge.

Lets try to calculate the force between two such "charged" objects placed at a distance og $1$ metre.Using Coulomb’s law we get,

$$F=\frac{kq^2}{r^2}\approx 10^9 N$$

That's too big a force.The forces we deal with in everyday life are generally order of a $N$ or a $kN$.Since we don't feel any such force the only conclusion can be they are exactly equal.

So to make a long answer short:It is an experimental fact.

Sandesh Kalantre
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