This question refers to the moment of the emission. Suppose the electrons get emitted in a small beam. Are the spins of the emitted electrons in the moment of their emission are showing all in different directions?

Since the emission takes place at least only when there is a potential difference the electrons get accelerated after emission. Are the spins of this accelerating electrons are showing all in different direction too?

  • $\begingroup$ Why wouldn't they be? What is emitting electrons in your question? $\endgroup$
    – Floris
    Apr 7, 2015 at 8:21
  • $\begingroup$ @Floris Nothing specail designed. Some piece of metal. $\endgroup$ Apr 7, 2015 at 8:58

1 Answer 1


Quantum mechanic predicts, that the allowed directions of the spins are quantized. This is one of the main findings of the Stern–Gerlach experiment. In a thermal beam I suppose the the spins to be equally in up and down. (There is no reason why they should not.) But "up" and "down" only correspond to a specific direction in space if there is an external magnetic field breaking the spherical symmetry. So I would conclude that the spins are showing in all directions.

But (as the Wikipedia article mentions): It is difficult (if not impossible) to repeat a Stern-Gerlach experiment with free electrons since they are not neutral and thus the Lorentz force gives you a hard time.

  • $\begingroup$ I agree with your conclusions of the first part of the question. What is about the second part? $\endgroup$ Apr 7, 2015 at 8:43
  • $\begingroup$ If the electrons are emmited by a thermal source there is no need for a potential difference. A static electric field alone will not change the direction of the spins. $\endgroup$
    – bernd
    Apr 7, 2015 at 8:47
  • $\begingroup$ Perhaps a misunderstanding. It seems to me that we are talking about the same. There has to be plate or somthing else with less electrons then protons. $\endgroup$ Apr 7, 2015 at 8:51
  • $\begingroup$ Could you answer this question too, please? $\endgroup$ Apr 7, 2015 at 10:33
  • $\begingroup$ All directions are possible until you try to observe them. The observation forces spin along a particular axis. QM "allows" any direction. $\endgroup$
    – Floris
    Apr 7, 2015 at 11:26

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