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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Original artwork by Windows to the Universe staff (Randy Russell).

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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