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I partially get it but don’t completely understand what is weird about it. Please tell me what I’m getting wrong.

Lets say North(stronger) is on the top and South on the bottom.

I understand the next two bits:

  1. Dipoles entering perfectly aligned with north(top) south(bottom) will be deflected down by the maximum amount. (or will they just rotate 180 degrees and deflect up?)

  2. Dipoles entering perfectly aligned with south(top) north(bottom) will be deflected up by the maximum amount.

What I don’t understand is why dipoles entering at angles e.g. north(45 degrees from top) don’t immediately align themselves with the magnetic field like a compass needle would, and then proceed as 1) or 2) and therefore, all end up with the maximum deflection?

All the explanations I’ve seen seem to think the dipole should not align itself north-south, and should therefore only deflect partially (filling the gap in the middle).

What’s the reason that the dipole can’t align itself north-south?

A) moving too quickly – it’s out of the magnet before it can turn?

B) Angular momentum (Larmor precession) resisting the turning force?

C) something else?

Or have I got this completely wrong and the dipole does align itself, but the quantization isn’t to do with the direction of the angular momentum, but the magnitude of it?

Were they expecting the magnetic dipole moments to have random magnitudes (and thus be deflected proportional to the magnitude)?

Does the angular momentum play any part in this experiment, or does it just produce the magnetic dipole moment?

Lau_gu
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1 Answers1

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When a magnetic dipole is deflected by the magnetic field it releases the potential energy as light as it comes to rest. We measure the amount of deflection and therefore the initial orientation of the dipole by measuring the energy of the released light.

If the dipole is already aligned with the magnetic field then it stays that way, and no energy is released.

If the dipole is not aligned with the field then classically we expect it to rotate to align with the field and release an amount of energy proportionate to the amount of rotation.

If the dipole is aligned exactly opposite with the magnetic field then it is deflected the maximum amount of 180 degrees, and the maximum amount of energy is released.

The "strange" reality is that we only observe 2 outcomes: 1. No energy is released, i.e. the dipole was aligned with the field, or 2. The maximum amount of energy is released, as if the dipole was aligned opposite to the field. We never observe energy associated with any angle in between.

What's more weird is that even if we set up the particle to be aligned at an angle in between aligned and oppositely aligned (by putting it in a magnetic field pointing in the desired direction), we still only observe the 2 above mentioned outcomes. If we do the experiment many times we find that the angle only changes the probability of which of the 2 outcomes will be measured, depending on how close the initial orientation is to either outcome.

Er Jio
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