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6 Magnet Station
Magnetic property of iron
A magnetized iron bar has its power concentrated at two ends, its poles; they are known as its
north (N) and south (S) poles, because if the bar is hung by its middle from a string, its N end tends to point northwards and its S end
southwards. The N end will repel the N end of another magnet, S will repel S, but N and S attract each other. The region where this is
observed is loosely called a magnetic field. Either pole can also attract iron objects such as pins and paper clips. That is because
under the influence of a nearby magnet, each pin or paper clip becomes itself a temporary magnet, with its poles arranged in a way
appropriate to magnetic attraction.
Fundamental nature of magnetism is not associated with iron magnets but with electric currents
The magnetic force is basically a force between electric currents. Bend copper wires into circles with constant separation (figure
below):
--Two circular currents in the same direction attract each other.
--Two circular currents in opposite directions repel each other.
Replace each circle with a coil of 10, 100 or more turns, carrying the same current: the attraction or repulsion increase by an
appropriate factor. In fact, each coil acts very much like a magnet with magnetic poles at each end (an "electromagnet"). Ampere
guessed that each atom of iron contained a circulating current, turning it into a small magnet, and that in an iron magnet all these
atomic magnets were lined up in the same direction, allowing their magnetic forces to add up.
Magnetism is light
Today electromagnetic fields (and other types of field as well) are a cornerstone of physics. Their basic equations,
derived by Maxwell, suggested that they could undergo wave motion, spreading with the speed of light, and
Maxwell correctly guessed that
this actually was light and that
light was in fact an
electromagnetic wave.
Heinrich Hertz in Germany,
soon afterwards, produced such
waves by electrical means, in
the first laboratory
demonstration of radio waves.
Nowadays a wide variety of
such waves is known, from
radio (very long waves,
relatively low frequency) to
microwaves, infra-red, visible
light, ultra-violet, x-rays and
gamma rays (very short waves,
extremely high frequency).