What causes magnets to be bipolar? Why, for instance, not
tripolar? Why is magnetic north always north and magnetic south
always south? (Except during reversals.) I am learning about
electromagnetism and particularly domain theory in school, and I
could not find a satisfactory answer on the web or in my textbooks.
Magnetic field is bipolar because a magnetic field at one position can
have only one direction. There is not uniform magnetic charge, so a
magnetic field cannot just point outward or inward like an electric
field. A magnetic field forms continuous loops. At any point on the
loop, it can have only one direction, appearing to point from one
direction to another.
A magnet tends to align itself with the magnetic field around it. North
and South for magnets are "north-seeking" and "south-seeking" when
stated completely. The north end of the Earth is a south-seeking
magnetic pole. The south end of the Earth is a north-seeking magnetic
pole. Opposites attract for magnets. The north-seeking pole of a
magnet is drawn toward the south-seeking pole of the Earth (i.e. the
north end). If the magnetic field of the Earth should reverse, the
south end would become the south-seeking pole.
Dr. Ken Mellendorf
Illinois Central College
Neither classical electromagnetic theory, nor quantum mechanical
electromagnetic theory excludes the possibility of the existence
of a magnetic "monopole" analogous to the electron. However, attempts
to find the "beast" to date have not been successful -- but not for
lack of effort.
The discovery of a magnetic monopole is a Nobel Prize waiting to be won!!
The "reason" you do not find this discussed in high school texts
(or many introductory college texts either) is that the "reason"
involves vector algebra and calculus -- math that has not been taught
at those levels, at least not yet.
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Update: June 2012