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Magnetism
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Question:
I am doing (creating ) a curriculum for MOSI, in Tampa, and need to
know what is going on now and what are planned future applications of
magnetism. Where can I find this info. online?
A science question: Do we really know how all the forces are related--
elec. mag. nuclear electromagnetic waves? and just what happens at the atomic
level when a substance become magnetic?
Replies:
I am not sure about where to find the online info you
asked about, but I can tell you that electricity and magnetism
were linked together during the mid-latter 1800's by James C. Maxwell
and others...at least from a fields point of view. The current
theories have linked together all of the forces successfully
(electromagnetic, nuclear, weak, etc.) except for gravity
(PLEASE do not flame me for this, you theoretical physicists
out there - I know that string theory pulls in gravity too but
from my understanding it is not yet universally accepted,
however elegant its form).
Now, for the other question; a substance becomes magnetic when
a few things happen. First, you must realize that each electron
has a small magnetic "moment", i.e., it responds to an external
magnetic field by lining up either parallel (lowest energy) or
antiparallel (higher energy). Certain substances are said to
be diamagnetic..these have as many parallel orientations, or
"down spins,", as they have antiparalle, or "up spins." Diamagnetic
substances are not magnetizable. Other substances have more ups
than downs, or more downs than ups, and these are said to be either
paramagnetic or ferromagnetic. Imagine that these substances each
have a little bar magnet (which is the sum of the bar magnetics of
all the electrons) on each atom. Now, if the interaction between
"bar magnets" is strong, all the bar magnets will tend to want to
point in the same direction, EVEN in the ABSENCE of an external magnet.
Such substances are said to be "ferromagnetic" and can be "permanently"
magnetized (actually if you whack a ferromagnet hard enough, you can send
a strong shock wave through the material and disorganize the
atomic bar magnets, demagnetizing the substances).
Finally, some substances have a weak spin-spin interaction
and are not permanently magnetizable; these are paramagnetic
materials. Liquid oxygen is paramagnetic; if you pour liquid
oxygen between the poles of a magnet, the stream is deflected.
However, liquid nitrogen is diamagnetic; in the same experiment
the stream is unaffected.
I have glossed over quite a few details in this explanation, and
resorted to a fundamentally simplistic way of thinking about
electron spin...but I hope that this explanation suffices.
Topper
Actually both nitrogen and oxygen streams would be deflected. The
distinction is that diamagnetic substances (nitrogen) are repelled from
regions containing magnetic fields while paramagnetic substances (oxygen)
are attracted into them.
Some of the most exciting applications of magnetism have to do not so
much with static as dynamic properties, and all substances exhibit dynamic
magnetic properties. A particular example is nuclear magnetic resonance,
which gives all kinds of important information about chemical structure ---
e.g. the shape of proteins --- and about chemical and physical events ---
e.g. how photosynthesis works. An extension of this is magnetic imaging in
medicine. This allows "photographing" the inside of the body without the
use of X-rays. Also, the conductivity of the body muddles up electrical
signals such as one gets from the brain (EEG's) and heart (EKG's), but does
not do the same with magnetic signals. You can therefore map in 3
dimensions electromagnetic activity inside the body by detecting the
magnetic field. (This usually requires "superconducting quantum inter-
ference detectors" or SQUIDs.) This has been used to study normal activity
--- e.g. the changing activity of the brain as one thinks, speaks, or re-
members --- as well as pathological activity --- e.g. the exact location of
defective tissue sparking epileptic seizures or cardiac arrhythmias has
been located in some people, allowing therapeutic intervention.
The National High Magnetic Field Laboratory has recently relocated to
the University of Florida at Gainesville, so there should be a lot going on
right in your neighborhood, so to speak.
christopher grayce
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Update: June 2012
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