Sunday, August 07, 2005
Weird Science: Magnetism
Animal, mineral or vegetable? Oh, sorry - been watching way too much Black Adder lately.
Let me restart - and we will concentrate on mineral.
So, what is Magnetism?
Magnetism is a mysterious force of interaction (not unlike opposite sex relationships), but although mysterious it is well known and highly predictable. And I haven’t answered the question yet, have I.
Well then, magnetism is the force of interaction between wires carrying electrical current, between magnets, or between a magnet and a magnetic material. It is the result of the motion of electrical charge at a subatomic level. It’s mysterious. You didn’t expect a clearer answer, did you?
And who, you may ask, started wondering about this strange force and how did it get discovered and then used?
Well the story goes that a shepherd from Asia Minor, called Magnus, got to wondering why bits of soil (naturally magnetic ores in the dirt - called magnetite or loadstone) would cling to his crook (metal top of his staff) and align in orderly directions.
Which gets me to wondering why the top of his shepherd’s staff ended up in the dirt - maybe a few local farm girls could answer that one. Ahem, anyhow, this strange and mysterious behavior (the ore clinging to the crook, not Magnus’s farm girl exploits) got him to passing the information around, likely eliciting strange looks from others - especially farmer’s who had sweet innocent daughters to raise...
Anyhow, by 2700 BC or so, the Chinese took that information and noted that certain materials (loadstone or magnetite again) always pointed in the same direction. This lead to the development of the compass (using pieces of loadstone suspended freely) which then got passed along to Marco Polo who brought the idea back to Europe around 1000 AD.
Once in Europe, this mysterious discovery was quickly used by sailors to point their way north. Or so the story goes.
The idea that magnets had poles (magnetic poles of north and south, not poles for long jumping) was formulated by Petrus Perigrinus in the 13th century.
Later, in the 16th century, Gilbert (as in William the brilliant scientist) explained that the earth itself has magnetic properties and is in fact a large magnet. He also noted that like poles repelled each other and opposites attract. He also found that a single pole can not exist by itself. When a magnet is broken in two, the two separate pieces each retain a north and south pole.
So hop in the time machine and watch the discoveries whizz by. The laws describing the force between two magnets were formulated by many scientists in the 18th century, most notably Charles Agustine de Coloumb. In the 19th century Hans Christian Oersted noted that current carrying wire could swing a compass needle. One year later Andre Marie Ampere showed that coiled wire with an electrical charge acts as a magnet. Then, shortly after Dominique Arago found out that steel could be permanently magnetized by Ampere’s coiled charged wires.
Skipping ahead some more, we see the previous discoveries put to use by William Sturgeon and Joseph Henry in the form of powerful electromagnets.
Then in the 19th century Michael Faraday finds that exposing wire to a changing magnetic field produces electrical current. This is known as Faraday’s law - an electric unit called the Farad named in his honor.
And there is just way much information relating to electricity for one post related to magnetism so will be explored in other weird science articles to come on a more specific basis.
And to think, just because a shepherd was messing about on the ground, this whole electro-magnetic thing became known leading to maglev trains, MRI scanners and computers.
You just never know.