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As we all know, if we rub ebonite rod with a fur, the rod becomes negatively charged(electrons get passed from fur to rod). But what happens if we will do that many times with the same fur but each time with another ebonite rub? I mean, is it possible that once(at one point) all electrons in this fur will run out? The fur without electrons? And, how can we to restore a previous state of this fur (with balance of protons and electrons)?

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The reason electrons leave the fur is that there is a favorable potential difference between the electron in the outer shell orbit, and an electron in an outer shell orbit in the rod. (This is a bit of a simplification, but not a misleading one.)

If you were to do this act many times, stealing many electrons (and a lot of negative charge) from the fur, the fur would eventually have a perceptible net positive charge, which could be considered as a charge-per-unit-area $\rho$. This will change the net effective potential for an electron to leave. If $\rho$ becomes big enough, the electrons will stop leaving.

Mind you, at that point, the fur still has plenty of electrons, and even plenty of outer-shell electrons left. It's just that you can't strip any more by rubbing with an ebony rod. However, gradually the fur will regain its electrons from the air, so if you wait long enough, it becomes a good source of electrons again.

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  • $\begingroup$ Is this to say if you had a bunch (call it a thousand) of ebony rods with gradually increasing electrostatic charge (with the first one uncharged and the last one half of the charge accrued by the first one with a linear distribution of charge in between) held in a vacuum and rubbed them one after another on the same fur the last one would not develop any charge? Another way to say this: would subsequent rods in a vacuum with the same initial charge each have reduced charge than those preceding them in a similar scenario? $\endgroup$
    – CoryG
    Dec 6, 2016 at 0:53
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You can only remove the outer shell free electrons. It is impossible to get electrons free this way as you may just get a large maximum charge.

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The ebonite rod is a good conductor, so electrons will be floating on every part of it's orbit having sufficient electrons on it's highest energy level. The fur is just like the carbon atom that is a solid but a non metal, chemically the carbon atom has 2 inner electrons and 4 valence outer electrons which it really doesn't give away. So electrons are donated by the ebonite rod, and the ebonite rod becomes negatively charged.

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