The magnetic field in Stern-Gerlach

In summary, the Stern-Gerlach experiment uses a nonuniform magnetic field to interact with the magnetic moment of the electrons, causing them to divert based on their spin value. This effect cannot be explained by a uniform magnetic field, and is important in understanding quantum physics. The magnetic field can be created using an electromagnet or a permanent magnet, and its strength and direction can determine the direction of the electron's deflection. The electron's spin value can be thought of as a "north" or "south" pole, and a collection of like spin electrons or protons can create an asymmetrical magnet with varying pole strengths. The concept of the electron "flipping" or changing its spin direction is not applicable in this experiment.
  • #1
Chen
977
1
In the Stern-Gerlach experiement, what's so special about the magnetic field that causes the electrons to behave like they do? How would you explain this in layman terms?

We learned that whenever a charged particle passes through a 'normal' magnetic field, a force F = qvB acts upon it, unlike the magnetic field in that experiment which causes the electrons to divert based on their spin value.

Thanks,
 
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  • #2
The important interaction in the Stern Gerlach experiment is not the charge of the electron with apparatus, but the magnetic moment of the electron with the apparatus. For a uniform magnetic field, there would be no displacement, but the Stern-Gerlach magnets produce a nonuniform field that is increasing along one direction.
 
  • #3
Chen said:
In the Stern-Gerlach experiement, what's so special about the magnetic field that causes the electrons to behave like they do? How would you explain this in layman terms?

We learned that whenever a charged particle passes through a 'normal' magnetic field, a force F = qvB acts upon it, unlike the magnetic field in that experiment which causes the electrons to divert based on their spin value.

Thanks,

hi
this is rajarshi please can you tell me how the non uniform magnetic field :confused: is arranged for Stern-Gerlach experiement.
what is the mathematical analysis envolved in this?
 
  • #4
It are silver atoms that are used in the Stern-Gerlach experiment, since these are neutrally charged as a whole, the Lorentz force is not the cause of this effect. Like slyboy said, it's the magnetic moment interacting with the strongly nonuniform magnetic field that does it.

I guess the magnetic field is created with an electromagnet, but I think a permanent magnet would also work. If the edge of the north pole of the magnet is very sharply peaked and the south pole is smooth, the field lines are much 'denser' near the north pole than near the south pole so you get a very nonuniform magnetic field.
Lots about it can be found on the net, just google stern gerlach.
 
  • #5
To imagine what is happening in the Stern-Gerlach experiment from a classical point of view, consider what would happen if you threw a bar magnet into a region with a magnetic field.

The north end of the magnet would be attracted one way in the field, while the south end would be attracted in the other. If the field were uniform, these two forces would cancel. The effect of a uniform magnetic field would be to apply a torque on the bar magnet, but it wouldn't cause it's center of mass to change.

On the other hand, if the magnetic field were not uniform, then the two ends of the bar magnet would experience different strength magnetic fields, and it would be possible for the magnet to have its center of mass moved in one direction. Of course if the magnet were reversed, the force would reverse too, so there you have it, a non uniform magnetic field will spread magnets out while a uniform magnetic field does not.

If you happen to find a magnetic monopole, well it would be attracted to one end or the other of even a uniform magnetic field. But we know that these things are hard to get, so the best we can do is to use a magnetic "dipole". And as illustrated above, a dipole can only be influenced, in terms of an overall force acting on the center of mass, when the dipole is placed in a non uniform magnetic field.

The quantum effect is similar. Hope this helps your intuition on the problem. The Stern-Gerlach experiment is very very important to an understanding of quantum physics.

Carl
 
  • #6
hmm, pardon my stupid question, but could it be that electrons are magnetic monopoles that can come in two different directions, a north and a south (spin up, spin down)? and a bar magnet has two directions due to the pretty much 50/50 split of different spin-oriented electrons? then would this mean that if you isolated a bunch of like spin electrons and protons (or atoms) made a magnet out of them, it would have assymetrical pole strength?

hmm. then again, viewing things this way would only cause problems with bosons...
 
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  • #7
Why doesn't the electron "flip"?

I know this thread is older than the hills...

Why doesn't the "bar magnet" (the electron) "flip" if the poles are "backwards", which would have the consequence of showing one deflected beam instead of two? I would intuitively expect the force pushing the electron away would be unstable, like balancing a ball on the head of a pin. More like if you had a bar magnet resting on a low friction surface and approached with a repulsive pole, it would flip and move toward the magnet in your hand.

Is this because the electron is tied to the silver atom and can't flip?

Is it due to some QM equivalent of precession?

Or is it just a breakdown of the analogy, where there is no classical explanation?

None of the above?

I know I am on thin ice with the classical analogy, but I want to take it as far as I can before it blows up.
 

1. What is the Stern-Gerlach experiment?

The Stern-Gerlach experiment is a classic experiment in quantum mechanics that was first performed in 1922. It involves the use of a magnetic field to split a beam of particles, usually atoms, into two distinct paths.

2. How does the magnetic field in Stern-Gerlach work?

The magnetic field in Stern-Gerlach works by exerting a force on a particle with a magnetic dipole moment. This force causes the particle to deviate from its original path, resulting in the splitting of the beam.

3. What is the significance of the magnetic field in Stern-Gerlach?

The magnetic field in Stern-Gerlach is significant because it demonstrates the quantization of angular momentum in particles. This was a groundbreaking discovery in quantum mechanics and helped to shape our understanding of the behavior of matter at the atomic level.

4. Can the strength of the magnetic field in Stern-Gerlach be adjusted?

Yes, the strength of the magnetic field in Stern-Gerlach can be adjusted to produce different results. By changing the strength of the field, the degree of deflection of the particles can be altered, allowing for more precise measurements and observations.

5. What other applications does the magnetic field in Stern-Gerlach have?

The magnetic field in Stern-Gerlach has been used in various applications such as particle accelerators, mass spectrometry, and magnetic resonance imaging (MRI). It is also used in research to study the properties and behavior of particles at the atomic and subatomic level.

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