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Suppose I have a large hunk of metal (make whatever assumptions about it being monocrystalline and 100% pure you like). If I erect the metal in a gravitational field (equivalently: submit it to constant acceleration out in space) will there be any separation between the positive and negative charges? In which direction?

The way I see it, if the external forces are transmitted primarily by the free electrons (effectively a bound plasma), then the negative charge will lead the positive charges causing a negative net charge on the top. If the forces are transmitted primarily by the interactions of the bound electrons (effectively, a frozen set of positive ions) then there will be a net positive charge on top. I lean toward the latter, but would love to learn the truth.

In a similar vein you could, instead of accelerating the metal or letting it sit there in a gravitational field, shape the metal into a disk and set it rotating about its axis of symmetry (or even rotate a bar about an axis perpendicular to it). In the absence of any magnetic field to induce currents, will a potential difference build up between the center and edges of the rotating disk?

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  • $\begingroup$ Why "the external forces are transmitted primarily by the free electrons"? I thought the gravitational force applies to all particles in the same way due to the equivalence principle. $\endgroup$ Commented Dec 27, 2016 at 15:50
  • $\begingroup$ This is less about the gravity, which will have a tiny tidal effect, than about the normal force that counteracts the gravity. In other words, this isn't about freefall, but about sitting there on the surface of a planet, or the locally equivalent accelerating in a rocket ship. $\endgroup$ Commented Dec 27, 2016 at 17:51

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There is the beautiful paper on determination of the Cooper pair mass in superconductors. This experiment is similar to your suggestion about disc, but superconductivity allows to remove scattering from the problem. As you will find out, the experimental result do not coincide with theoretical estimate, so role of gravity on QM particles is not that simple. So the short answer to your question: yes, there is gravitational effect and no, it is not that simple.

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