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This is probably a very stupid question but I couldn't find an answer on google.

Consider a neutral material - say, some block of metal. There is exactly as many electrons as protons and the electrons are bound to the nuclei with the electromagnetic force.

Now, add some electrons to it. It becomes negatively charged, until something with a lower charge contacts it.

The electromagnetic force makes negative charges away from other negative charges.

So why doesn't the object directly repel its overload of electrons? What prevents them to escape into the vacuum? Is there another interaction that I don't know which is occuring?

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  • $\begingroup$ It is a mobility of electrons in metal that makes the metal locally charged positively due to going away the metallic electrons. So the resulting attraction may become sufficient to bind an extra electron to the bulk of metal. $\endgroup$ – Vladimir Kalitvianski Aug 25 '19 at 8:44
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The electrons do feel mutual repulsions and so will spread out, to an extent that their repulsion will be overcome by attractions of nearby protons. Increasing distance reduce the force, and attration due to protons don't let them fly off into space.

But this happens only to an extent. Keep adding more negative charge, and you'll reach a point when electrons are able to fly off. This results in phenomenon such as Corona discharge.

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