What keeps electrons on wires?

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Discussion Overview

The discussion revolves around the mechanisms that keep electrons bound to current-carrying wires, particularly in the context of external magnetic fields and the forces acting on the electrons. Participants explore both classical and quantum mechanical perspectives, as well as practical examples like X-ray tubes and van de Graaff generators.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions what prevents electrons from leaving a wire when subjected to a magnetic force, suggesting that strong currents or magnetic fields might overcome this barrier.
  • Another participant asserts that electrons lack sufficient kinetic energy to escape the potential well created by the atomic structure of the wire, but acknowledges that electrons can be removed under certain conditions, such as in X-ray tubes.
  • A question is raised about whether classical physics suffices to understand the situation or if quantum mechanics is necessary, particularly regarding the nature of the attractive forces holding electrons in place.
  • One participant explains that while electrons in a wire are bound to the crystal lattice, they are not as tightly bound as non-valence electrons, noting the difference between mean velocity and drift velocity of electrons.
  • Another participant introduces the concept of resistance in wires and references historical experiments with 'exploding wires' that demonstrate the effects of excessive current.
  • A participant emphasizes that electrons in a wire are part of atoms and are attracted to protons, while also discussing how metals allow for electron mobility due to the collective behavior of atoms.
  • The discussion includes a mention of the van de Graaff generator, illustrating how electrons can be stripped from surfaces and the conditions under which they may escape into the atmosphere.

Areas of Agreement / Disagreement

Participants express varying views on the forces acting on electrons in wires, the role of resistance, and the applicability of classical versus quantum mechanics. There is no consensus on the primary mechanisms at play or the sufficiency of classical explanations.

Contextual Notes

Participants reference specific phenomena like the Hall Effect and historical experiments, indicating that the discussion may be limited by assumptions about the nature of electron binding and the definitions of forces involved.

Zorodius
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say you have a current carrying wire pointing in the +x direction, while there's an external magnetic field pointing in +y. Then the electrons in the wire feel a force towards +z.

Well, what stops them from flying off the wire? If you make the current or the magnetic field strength strong enough, can you overcome whatever it is, and tear the electrons off the wire?
 
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They don't have enough kinetic energy to overcome the potential from the atoms.

But or course in certain circumstances electrons can be ripped of the conductor, look how an X-ray tube works for example.
 
could I understand this classically, or would I need quantum mechanics to understand it?

Is the potential you describe due to an attractive nuclear force?

If such a force acts on the electrons to hold them on the wire, why are they still free to move through the body of the conductor?
 
The electrons are not totally free. They are bound to the crystal (the wire), but not as bound as the non-valence electrons are. The electron in the wire as (mean)velocites about 10^6 m/s, but the drift velocity (the velocity the electrons will get EXTRA due to the applied electric field) is only about 1mm/s !

And you sould also perhaps look at the Hall Effect, try google it and see if you get wiser.
 
interesting, thanks!
 
My understanding is that wires have resistance and that current travels through or over the surface of the wire. If there is less resistance over the surface, then where do you think they will go. That is not to say that electrons do not flow through the wire. In the 60's we did experiments, 'exploding wires', where the wire could not handle the current. It produced miniature 'ball lightning'.
 
Remember, Zorodius, an electron on a wire is still part of an atom. It is attracted to the atom's protons by the same magnetic force that any other atom has. But the thing about metals is that when you put a lot of atoms together, they act like one group of combined charges, allowing the electrons to be mobile as long as they keep the overall charge roughly neutral.

Now what if we make the overall charge negative? Have you heard of a van de Graff generator? It uses a belt and brushes (I think...) to strip electrons and put them on a metal sphere much like your shoes strip electrons off a carpet when you shuffle your feet. Those electrons do want to jump off the metal sphere and they collect on the surface of the sphere, slowly dissipating into the atmosphere. Give them an easier path (like through your finger), and they will jump off all at once, bringing the charge on the metal sphere back into equilibrium.
 

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