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We are learning about the Hall Effect in high school, but what confused us was that hypothetically if both protons and electrons were moving, but electrons moved much faster, then wouldn't there still be a weaker Hall voltage? How do we experimentally know that only electrons move?

Obviously, since protons are held together with the strong force, it's much more likely that only electrons would move. But how can it be shown experimentally?

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  • Experiments with cathode rays were ealy evidence. – M. Enns Apr 03 '18 at 01:20
  • @M.Enns: That was evidence that electrons existed in the first place, not that electrons are the free charge carriers in metals. –  Apr 03 '18 at 02:37
  • " since protons are held together with the strong force" please note that the strong force holds the protons and neutrons within an atom. The metals (and solids and liquids) interact with the electromagnetic forces that exist between atoms and molecules. see my answers https://physics.stackexchange.com/questions/262280/if-a-water-molecule-is-neutral-how-do-water-molecules-attract-one-another-by-el/262315#262315 and https://physics.stackexchange.com/questions/209230/how-does-crystal-lattice-explain-electrical-conductance/245439#245439 . The electrons in the conduction band can move – anna v Apr 03 '18 at 05:50
  • in the whole solid , almost as free, while the nuclei are in fixed positions in the lattice of the solid, as holding most of the mass. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/bravais.html#c1 – anna v Apr 03 '18 at 05:51

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It's not true in general that electrons are the charge carriers in electric currents. For example, electric currents in your nervous system are carried by various ions.

The most direct evidence that the charge carriers are electrons in the case of a metal comes from the 1910 Stewart-Tolman experiment, in which a coil of wire was rotated rapidly and then abruptly stopped. The inertia of the electrons caused a current to flow, and the charge-to-mass ratio was verified to be that of the electron.

Obviously, since protons are held together with the strong force, it's much more likely that only electrons would move.

This only makes it unlikely that it's protons, but not that it's nuclei or ions.