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A base-level question about electromagetism, magnetic fields, & conductors

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ejeffrey:

--- Quote from: RJSV on October 04, 2023, 11:51:32 pm ---   In my training, a pure beam of electrons will repel each other, (being 'like' charges), which are focused in the CRT case, to counter the tendency to spread out during travel.
Actually surprised, that similar situation, going down a wire, isn't the same, as far as the generated magnetic field, thinking the atoms etc. in a copper wire will have positive charges that balance the negative (moving) charges.  Or did I read previous posts wrong ?
(thanks)

--- End quote ---

Yes.  The copper nucleii provide a positive charge to balance out the electrons and make the whole thing net neutral.  This creates a screening potential that reduces the effective range of the coulomb interaction dramatically and allows electrons to approximately move as free particles.


That's basically why we have wires.  Electron beams in vacuum theoretically have "zero resistance" but you are limited to very low density of charges before the mutual repulsion causes a problem.

Conductors are a bunch of positive charges that allow you to cram many orders of magnitude more electrons in a given space and conduct a lot more current.  The problem is that the positive charges tend to get in the way of the electrons.  What makes a good conductor is that the nuclei arrange themselves such that they screen the charges while still allowing free movement of the electrons.

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