Say I wrapped a piece of wire around an iron bar in a closed circuit connected to a DC power supply, the electrons starts flowing and moving charge produce magnetic field. Yet a bar magnet can produce a magnetic field without any charged particles moving around, are the magnetic fields produced by the two objects different types?
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2$\begingroup$ Electrons are moving inside any permanent magnet (including the bar magnet) in a certain ordered fashion, which is why they produce magnetic field. In a way, there are current loops aligned with each other inside a permanent magnet. In an ordinary (non-magnetic) material these loops are disordered and do not produce net magnetic field $\endgroup$– Yuriy SJan 20, 2016 at 6:50
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2 Answers
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All macroscopic objects we observe are emergent from the underlying particle/atomic/molecular nature, which by the way follows quantum mechanical equations.
a) The reason we see electric fields is fundamentally because electrons and protons have electric charge, which generates their electric field. There are many ways that electric fields can be macroscopically induced. Analogously, the reason we see magnetic fields is because particles/atoms/molecules have magnetic dipole moments inherent in their nature, which have elementary magnetic fields.
b) A second source of electric and magnetic fields comes from the behavior of elementary and fields under motion: they obey Maxwell's equations, which tell us that changing electric fields generate magnetic fields and changing magnetic fields generate electric fields.
Say I wrapped a piece of wire around an iron bar in a closed circuit connected to a DC power supply, the electrons starts flowing and moving charge produce magnetic field.
A magnetic field is generated from the moving charges due to the laws of b), and the small dipole ferromagnetic domains described in a) orient themselves according to the external field and magnetism is retained even when the current is off. The current enhances the total magnetic field after first orientations of the dipoles.
Yet a bar magnet can produce a magnetic field without any charged particles moving around, are the magnetic fields produced by the two objects different types?
In a permanent magnet the domains after being oriented in a direction retain it because they are in the lowest energy state of the solid when oriented.
The magnetic field is the same type of field for all cases.
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$\begingroup$ So do you mean the magnetic field created by the bar magnet is due to the collective strength of all the electrons magnetic dipole aligning in same direction? and electron is a charged particle that have spin which explain its magnetic dipole moment? $\endgroup$– user6760Jan 20, 2016 at 7:57
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$\begingroup$ Not electrons, the magnetic domains are conglomerates of molecules that have magnetic dipole moments all aligned, but they are small and random if a magnetic field is not previously imposed. In permanent magnetic materials the new orientation is retained because it is energetically favorable. I have given a link. The magnetic moment of molecules appears because of the electron clouds connecting them: moving electric fields, except quantum mechanically, not classical electromagnetism, although it can be thought as an approximation. $\endgroup$– anna vJan 20, 2016 at 8:04
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$\begingroup$ For permamanent magnets the nuclear spin and magnetic moment are important. see this page for magnetic moment of iron hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nspin.html . It is not a simple story because quantum mechanics enters. $\endgroup$– anna vJan 20, 2016 at 8:11
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There is only one type of magnetic field, but there are multiple ways to generate a magnetic field. A bar magnet has a permanent magnetic field while a electromagnetic has a magnetic field only when the current is applied.
Another way to get a magnetic field is to induce one. So you place an iron bar near one pole of a bar magnet but not touching. The bar magnet will then induce a magnetic field on the previous nonmagnetic iron bar.
For superconductors you can float a magnet over them. The magnet induces an electrical current in the superconductor which creates a magnetic field within the superconductor. The magnetic field in the superconductor is opposite the magnet so the magnet floats over the superconductor (Youtube video).
