When studying the Stern-Gerlach experiment, books (and professors) usually consider a collimated beam that is eventually splitted by the interaction between magnetic moment and the non-homegeneous magnetic field. In this case, if the field is OFF you should be able to see a single point on the collector plate, and if the field is ON you should see two points (actually three). Like this:

The original Stern-Gerlach experiment results in sort of an "eye" shape. What is the cause of this elongated shape? I initially though that this was caused by the shape of the atoms beam (the first photograph of the next image shows a line, not a point), but in this case I can't wrap my head around why the extremities of the beam should touch and only split in the middle when the field is ON. Shouldn't I see two straight segments instead?

All help appreciated.

  • $\begingroup$ any sources for the picture? Maybe the field was not strong enough at the sides. $\endgroup$
    – lalala
    Commented May 9, 2017 at 14:08
  • $\begingroup$ Remember that the requirement is that the field is inhomogeneous. That occurs over some length scale. Should that length scale be similar to the width of the beam from the oven, you would see the shape indicated on the right in your picture. $\endgroup$
    – Jon Custer
    Commented May 9, 2017 at 14:31

1 Answer 1


The atomic beam was wider than the magnetic field so the atoms at the extremes did not feel much of a magnetic field. As the beam experienced a weaker and weaker magnetic field the separation became smaller.

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