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The magnet has its own magnetic field and the same goes for the compass. So whenever I place a compass near a magnet, the magnetic field lines of both the compass and the magnet must interact to produce a new magnetic field. Then why is the compass feeling a push or pull?

It may sound like a dumb question but can you please explain why a compass experiences the force?

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  • $\begingroup$ the magnetic field lines of compass and magnet must interact to produce a new magnetic field This “interaction” is merely superposition; they just add as vector fields. $\endgroup$
    – G. Smith
    Jan 18, 2021 at 18:28
  • $\begingroup$ universetoday.com/77072/how-does-a-compass-work/…. $\endgroup$
    – Gert
    Jan 18, 2021 at 19:01
  • $\begingroup$ @G.Smith Since the energy of the magnetic field is $B^2/\mu_0$ you can argue that the two fields interact. $\endgroup$
    – my2cts
    Jan 30, 2021 at 12:34
  • $\begingroup$ This is a very deep question to which physics has no answer. Physicist know how two magnets interact but do not know why (electro-)magnetism exists. $\endgroup$
    – my2cts
    Jan 30, 2021 at 12:37

2 Answers 2

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-Magnetic fields are generated by moving charges
-Magnetic fields exerts a force on moving charges

In your situation you can imagine (although it is a simplification) the moving charges
as the electrons orbiting around the nucleus in lined up orbits (lined up because it is a magnet)

So yes, the final magnetic field is generated by both the objects, but inside inside each object it is not zero, and since inside the objet there are spinning electrons, they experience a force. The the sum of the forces experienced by each electron is the one which makes the compass spin.

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    $\begingroup$ 'the electrons orbiting around the nucleus in lined up orbits (lined up because it is a magnet)' This is incorrect. Ferromagnetism originates from electron spin, not from electron orbital motion. $\endgroup$
    – my2cts
    Jan 30, 2021 at 12:30
  • $\begingroup$ Yes you are right, but then you would need to explain magnetic dipole moment and force dependent from the gradient of the magnetic field (since you can no longer imagine a moving charge and you could not imagine why it undergoes a force). That seemed to me an overkill of the question $\endgroup$ Jan 31, 2021 at 9:47
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Don't know if I understand your question, but I guess answer must be the compass is feeling a push or pull because the two magnetic fields you speak of want to align. That itself is a consequence of the effect magnets have on other moving electrons (magnets).

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    $\begingroup$ Can you please provide a source for a picture of the magnetic field lines created after the interaction of magnetic field lines of compass and magnet That will of great help! $\endgroup$ Jan 18, 2021 at 18:15
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    $\begingroup$ youtube.com/watch?v=NWUgK8W-4JM this shows the field lines, those of bar magnet are similar to compass, instead, the needle IS a magnet. I'm sure if you google there wil be much more similar results. $\endgroup$
    – 12know
    Jan 18, 2021 at 18:24
  • $\begingroup$ Why would two magnetic fields want to align? This is no answer. $\endgroup$
    – my2cts
    Jan 30, 2021 at 12:32

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