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Bar magnets have two poles. They produce dipole magnetic fields. Magnetic fields can have more than two poles - quadrupole fields have four.
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Dipole, Quadrupole, and Multipole Magnetic Fields

You are probably familiar with bar magnets. Bar magnets have two magnetic poles - north and south. The magnetic field around a bar magnet is called a dipole ("two poles") magnetic field. Bar magnets are not the only objects capable of creating dipole fields. Electricity flowing through a coiled wire can generate a dipole magnetic field. The magnetic fields of some planets, including Earth, are "more or less" dipole fields.

Dipoles are not the only shape magnetic fields come in. Quadrupole fields (four poles) are fairly common. Sometimes magnetic fields have six or even eight poles (an octupole!). Any field with more than two poles is called a multipole field.

Many astronomical objects have magnetic fields that are pretty much dipoles. However, some objects have complex magnetic fields that are a combination of a dipole and one or more multipole fields. The magnetic fields of Earth and Jupiter are strongly dipolar, with only minor multipole contributions. However, the quadrupole elements of the magnetic fields of Uranus and Neptune are similar in strength to their dipole portions.

Last modified May 5, 2009 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA