Deflection of magnetic dipoles by a magnetic field

[snoopies622]

I'm reading about the Stern–Gerlach experiment and the only part that confuses me is how a magnetic field would deflect particles with magnetic dipoles instead of just rotating them. In this case the magnetic field is non-uniform, but it still seems intuitively strange to me since magnetic field lines around the particles are always closed, and so I imagine that any magnetic field would have a kind of translational net zero effect on them. Would this translational force also appear if I tossed a macroscopic bar magnet through a non-linear magnetic field? (Say, one that always pointed in the same direction but increased in strength in a spacially linear way.)

 

[Dale]

I'm reading about the Stern–Gerlach experiment and the only part that confuses me is how a magnetic field would deflect particles with magnetic dipoles instead of just rotating them.

Suppose you are near the North Pole of your external non-uniform field. In that case your dipole’s North Pole will be repelled and the dipole’s South Pole will be attracted. However, since the South Pole will be closer to the external magnet the field there will be stronger than at the dipole’s North Pole, so the attraction of the South Pole will be stronger than the repulsion of the North Pole and you will have a net attractive force.

 

[snoopies622]

Thanks, Dale. It makes sense analytically but I guess I'll have to do some imagining and drawing pictures for it to work for me intuitively. I'm finding that thinking of gravitational tidal forces is a helpful analogy.