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Let us say we have a negatively charged conducting sphere:

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If we put an insulator into contact with the sphere: enter image description here

Would the negative charges located in the contact region transfer from the surface of the conductor onto the surface of the insulator that's in contact with sphere? Would the outcome be any different if the insulator was a dielectric?

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  • $\begingroup$ Vacuum is a very good insulator. The negatively charged sphere will hold charge for quite some time under low field conditions... $\endgroup$
    – Jon Custer
    Aug 15, 2019 at 22:10
  • $\begingroup$ @JonCuster But there is no reference to vacuum in the problem, the insulating rod is in direct contact with the sphere. $\endgroup$
    – Hilbert
    Aug 15, 2019 at 22:59

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It depends on how "good" your insulator really is. In an ideal theoretical situation your insulator may truly be an insulator: there's no free charge in it and the conductivity is exactly zero, hence the charge on the conductor will remain there. If the insulator is a dieletric with only bound charges, then the field of the free charges on the conductor will influence all the bound charges and make them rearrange a bit, polarizing the material (but creating no current).

In real life no material is an ideal insulator, so it allows some charges of the conductor to be transfered. But since the insulator has a poor conductivity, the charge transfered won't get very far and will concentrate on the interface between insulator and conductor.

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