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Q: Why does hitting a magnet with a hammer cause the magnetism to be reduced? A: Because hitting produces heat energy which would increase the mobility of atoms, increasing in this way the randomness of orientation of magnetic moments. Macroscopic net magnetism is due to predominant orientation of magnetic moments along a certain direction. Destruction of macroscopic net magnetism does not mean that individual atoms do not have a magnetic moment, but that the orientation of atomic magnetic moments is random. |
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Q: If the North pole of a magnet points toward the North pole of the earth, doesn't this mean that poles of the same sign, the magnet's North pole and the earth's North pole, are attracting each other? A: The end of a magnetic needle of a compass that points toward the magnetic North pole of the earth is the South pole of the needle. Usually it is marked with the letter N not because it represents the North pole of the needle but because it points toward the North pole of the earth. |
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Diamagnetic materials: materials which do not exhibit magnetism until they are place in an external magnetic field Bext. Then they develop a magnetic dipole moment directed opposite Bext. If the field is nonuniform, the diamagnetic material is repelled from regions of greater magnetic field. The property is called diamagnetism.
Paramagnetic materials: materials in
which each atom has a permanent magnetic dipole moment 
,
but the dipole moments are randomly oriented and the material as a whole lacks a
magnetic field. However, an external magnetic field Bext
can partially align the atomic dipole moments to give the material a net
magnetic dipole moment in the direction of Bext.
If Bext is non uniform, the material is attracted to
regions of greater magnetic field. Theses properties are call paramagnetism.
Ferromagnetic materials: materials, in the absence of an external magnetic field, in which some of the electrons have their magnetic dipole moments aligned by means of a quantum physical interaction called exchange coupling, producing regions (domains) within the material with strong magnetic dipole moments. An external field Bext can align the magnetic dipole moments of those regions, producing a strong net magnetic dipole moment for the material as a whole, in the direction Bext. This net magnetic dipole moment can partially persist when Bext is removed. If Bext is nonuniform, the ferromagnetic material is attracted to regions of greater magnetic field. These properties are called ferromagnetism. Exchange coupling disappears when a sample's temperature exceeds its Curie temperature, and then the sample has only paramagnetism.
Gauss' Law for Magnetic Fields: The net
magnetic flux through any (closed) Gaussian surface is zero.
Bohr magneton constant: 
| Gauss' Law for Magnetic Fields | |
| Spin magnetic dipole moment |  |
| Component (Sz) of S being measured along the z axis |  |
Component of (  s,z ) of s being measured along the z axis |
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| Potential energy (U) associated with the orientation of the spin magnetic dipole moment in an external magnetic field |  |
| Association of the electron's orbital
angular momentum (Lorb), with the orbital
magnetic dipole momentum (orb) |
 |
| Orbital angular momentum is quantized and can have only values given by |  |
| Magnitude of the orbital angular momentum |  |
| Potential energy (U) associated with the orientation of the orbital magnetic dipole moment in an external magnetic field Bext |  |
| Magnitude of the magnetization (M) of a paramagnetic material |  |
| Curie's Law |  |
| Maxwell's Law of Induction |
 |
| Ampere-Maxwell Law |  |
| Displacement current due to a changing electric field |  |
| Ampere-Maxwell Law (rewritten) |  |
[Top] [Previously Asked Questions] [References]
