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Fact File About Magnetism
2021/ All magnets have
two poles, labeled ``N'' and ``S''. You cannot have a single
magnetic pole (a ``monopole'') by itself. If you break a magnet
in half you get two magnets, each with two poles.
2022/ The Earth’s
magnetism has existed for 3 billion years and is generated
3,000 kilometres under our feet by the stirring of our planet’s
liquid iron core. This liquid iron core causes the Earth to
act like a giant magnet; the magnetic lines are organized
on a bipolar basis, more or less in alignment with the Earth’s
rotational axis.
2023/ The magnetic poles
of the earth are not located at the geographic poles. The
angle between the geo- graphic North Pole and the magnetic
"north" pole is called the magnetic declination.
The angle of declination depends on one's location on earth.
2024/ Sometimes magnetic
north and south switch, so the magnetic north pole is suddenly
near the geographic South Pole, and the magnetic south pole
is near the geographic North Pole. This is called magnetic
reversal and has happened hundreds of times over millions
of years.
2025/ The Earth's magnetic
field is called the "magnetosphere" and stretches
over 37,000 miles into space.
2026/ Many animals seem
to be able to detect the Earth's magnetism. The Arctic Tern's
migratory route follows the Earth's lines of magnetic force.
Many other animals such as caribou, sea turtles, whales, birds
and fish may also use the Earth's magnetism to find their
way.
2027/ After World War
II, submarine warfare equipment was put to good use. The sea
floor of the world's ocean was mapped using magnetic exploration
and depth-sounding devices. The first topographic maps of
the ocean floor were produced. Along with this came the discovery
that the ocean floor was actually moving thus supporting Arthur
Holmes' concept of plate tectonics.
2028/ The south pole
of the Earth's magnet (which attracts the north pole of a
compass needle) is called the North magnetic pole because
of its position. It is located 1200 miles from the geographic
north pole, off the Arctic shore of Canada.
2029/ The north magnetic
pole, first located (1831) by English explorer Sir James C.
Ross, is now about 78°N and 104°W in the Queen Elizabeth
Islands of northern Canada. The south magnetic pole, reached
(1909) by English geologists Sir T. W. E. David and Sir Douglas
Mawson, is now about 66°S and 139°E on the Adélie
Coast of Antarctica.
2030/ Pigeons, especially
those bred for their homing instincts, seem to be able to
detect the Earth’s magnetic fields. Cornell University
pigeon researcher Dr. Charles Walcott says that magnetic sensitivity,
along with an ability to tell direction by the sun, seems
to help pigeons find their ways home.
2031/ Uranus is greenish
due to the presence of methane in its atmosphere. Its magnetic
field is 50 times greater than Earth's, and is shrouded in
a thick smog composed of ammonia, methane, helium, and other
elements.
2032/ The earth's magnetic
field is decreasing. It has been determined that for the past
150 years its strength has decreased 6 percent.
2033/ The aurora borealis
("Northern Lights") is caused by the Earth’s
magnetic field and its interaction with ionized particles.
2034/ The magnetic poles
follow circular paths with diameters of about 100 miles (160
km).
2035/ The world produces
between 1 and 2 exabytes of unique information per year, which
is roughly 250 megabytes for every man, woman, and child on
earth. An exabyte is a billion gigabytes, or 1018 bytes. Printed
documents of all kinds comprise only .003% of the total. Magnetic
storage is by far the largest medium for storing information
and is the most rapidly growing, with shipped hard drive capacity
doubling every year.
2036/ The official definition
of a second is the time it takes for 9,192,631,770 oscillations
of the Cesium atom at zero magnetic field.
2037/ Not only do the
poles change their position, the magnetic field itself changes
in strength. In the early 1800s, the field was about 6 percent
greater than it is now. Around 1600 A.D., it was 50 percent
greater, but 5,500 years ago it was only about one-half the
present value.
2038/ To magnetize a
sewing needle rub it about twenty times on a magnet.
2039/ The magnetic stripe
on your credit card contains important information about your
account in magnetic code. Anything that de-magnetizes the
stripe can wipe out the code and make the card unusable. Some
common "de-magnetizers" are magnetic clasps on a
purse or wallet, televisions, and stereo speakers.
2040/ Magnetic resonance
imaging, or MRI, is a more recent brain imaging technique
that is rapidly gaining widespread use for identifying brain
disorders. This technique uses a magnetic field and radio
waves, rather than X rays.
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