# On the creation of the magnetic field in the Stern-Gerlarch experiment

My question is on the experimental setup of the Stern-Gerlach experiment, the model diagram in my textbook shows the magnetic field being created by a North pole and South pole magnet (I am assuming they are equal strength magnets, which may be incorrect).

Upon examining this picture though I realized that the magnetic field gradient say $$\frac{\partial B}{\partial z}$$ would be positive in the upper half plane and negative in the bottom half. This is confusing me as I know the force on the magnetic dipole is proportional to the magnetic field gradient, thus I would expect that this would influence the deflection, but this isn't mentioned in the text. So I am wondering if anyone knows how this is reconciled, or if perhaps in the real experiment the magnetic field was actually generated such that the gradient is constant in one direction throughout the region.

• I'm a little unclear on your description and how it's confusing you, the field in the picture has a gradient only in the z direction as required, and this is what deflects the silver atoms used. Also you should state what text your talking about so there is some context. Jan 10, 2022 at 7:09
• What is a North pole magnet? Jan 10, 2022 at 7:20
• It is unclear why you think the magnetic field gradient is "positive in the upper half and negative in the bottom half". You can improve the question by clarifying why you think that. Jan 10, 2022 at 12:54

(b) I don't understand about $$\frac{\partial B_z}{\partial z}$$ changing sign. Surely it's always negative in the gap between the poles, taking the $$z$$ direction as downwards (or upwards!). I think that the 3 black lines coming from the pointy bottom of the North Pole and diverging are representative magnetic field lines.