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An electron and a proton have opposite charges. But how can we be so sure that they have equal amount of charge but opposite? Can't there be a slight difference?

Qmechanic
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Strong Lizard
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1 Answers1

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Because of the huge number of protons and electrons present in a handy-sized chunk of matter (like, for example, a baseball), if there were even a very tiny difference in the magnitude of the charge between an electron and a proton in a single atom, that difference would give rise to macroscopic effects that could easily be measured. Those effects do not exist even at the scale of things like planets, so we have high confidence that those charges are exactly opposite and equal.

niels nielsen
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    I don't think this is a particularly convincing answer. For instance, if the proton had a charge 1.00000001 times greater than the the charge of the electron, then for a large chunk of matter to be electrically neutral, we'd just need to stick one extra electron floating about for every 10^8 protons to make things neutral. This would not be readily apparent. – Mason Nov 19 '19 at 19:48
  • @Mason Not readily apparent? In 1 mol of hydrogen atoms there would be a charge of $6~10^{15}~e$, i.e. about $10~^{-3}$ C. That is a sizable charge! (see for instance https://en.wikipedia.org/wiki/Orders_of_magnitude_(charge) ). – GiorgioP-DoomsdayClockIsAt-90 Nov 20 '19 at 00:31
  • You're missing the point, @GiorgioP. If there was a charge imbalance, you could just add extra electrons to offset the extra charge from the protons. So one mol of hydrogen, would have around $10^{15}$ more electrons in it than protons, which might be hard to measure. There's no law of the universe saying that there must be the same number of electrons as protons. – Mason Nov 20 '19 at 02:36