i wanted to know why does a moving charge and bar magnet not experience force similar to how two bar magnets experience since they both have magnetic fields. In bar magnets they attract or repel but in a moving charge there is just force? Can you tell what actually happens here?
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$\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$– Markoul11Commented Feb 16, 2022 at 18:24
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$\begingroup$ Atracting or repelling is a very basic example of a force, isn't it? $\endgroup$– HoodyCommented Feb 16, 2022 at 19:43
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2 Answers
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Charges like electrons apart of spin magnetic dipole moment posses also angular momentum like spinning tops that resist forces by an external stationary magnetic field like that of permanent magnets. Therefore their resulted trajectory taken under the influence of externally applied magnetic fields differs from what is expected from two normal magnets in attraction or repulsion.
It is called the magnetic part of the Lorentz force $F_{(M)}=q(\mathbf{v} \times \mathbf{B})$ (i.e. without an external electric field applied) when moving electric charges with spin interact with magnetic fields and the direction of Lorentz force and their trajectory can be found with the right-hand rule taking into account direction of magnetic field in space $B$ and direction of moving particle with velocity $v$.
image source: https://www.youtube.com/watch?v=dFT7-_s0jh0
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$\begingroup$ Since the spin of the electron is responsible for this then if one bar magnet was spinning would it bring the same effect? $\endgroup$ Commented Feb 24, 2022 at 5:34
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$\begingroup$ In practice, No. This was verified in the Stern-Gerlach experiment. The spin angular velocity of the electron for its charge radius is enormous! And never possible to be achieved with macroscopic matter. However, I must admit such an experiment with macroscopic magnetic spinning tops thrown in a Stern-Gerlach apparatus as far as I know was never attempted so far. $\endgroup$ Commented Feb 24, 2022 at 6:11
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Actually, we understand the magnetic force acting on a moving charge to be the "more fundamental" law from which you can derive the force between two permanent magnets. The derivation is suprisingly complicated.
