How Do Magnetic Forces Differ Between Magnets and Wires?

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SUMMARY

The discussion centers on the differences in magnetic forces between permanent magnets and current-carrying wires. It establishes that the force between two magnets aligns with the magnetic field lines, while the force between two wires is perpendicular due to the Lorentz force, which is defined as perpendicular to both velocity and magnetic field (B). The magnetic moment of iron filings aligns with the magnetic field, but the force experienced is along the magnetic field gradient, which can differ in direction from the field lines themselves. This distinction is crucial for understanding magnetic interactions in different contexts.

PREREQUISITES
  • Understanding of magnetic fields and forces
  • Familiarity with the Lorentz force law
  • Knowledge of magnetic moments and field gradients
  • Basic principles of electromagnetism
NEXT STEPS
  • Study the Lorentz force in detail, focusing on its applications in electromagnetism
  • Explore the concept of magnetic field gradients and their implications
  • Investigate the behavior of magnetic moments in various materials
  • Learn about the differences in magnetic interactions between static magnets and current-carrying conductors
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Students and professionals in physics, electrical engineering, and anyone interested in the principles of magnetism and electromagnetism.

nemuritai
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I understand the iron fillings become little magnets all pointing in the same north south direction similar to the spin aligned electrons in the permanent magnet.
Similarly, a compass near a wire traces out the magnetic field lines ie North/South.

My question is how do I reconcile the fact that the force of a magnet on another magnet is along the field lines whereas for two wires it is perpendicular? The latter is from the fact that the lorentz force is perpendicular to v and B, but why is the force of two magnets alongside the magnetic field instead of perpendicular?

Is the force alongside the B field in one and perpendicular in the other? What error have I made? Magnetic_field_of_bar_magnets_attracting.png
 
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An iron filing has a magnetic moment that experiences a torque that rotates it so that its long axis lines up with the local field lines. The force on it is along the direction of the magnetic field gradient which is not necessarily along the local field lines. In the case of the bar magnets that you show in the photo, the magnetic field and its gradient are roughly in the same direction. In the case of the infinite wire the magnetic field is in the azimuthal direction but its gradient is in the radial direction.
 
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