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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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