 - A magnetic field is generated when electric charge carriers such as electrons move through space or
within an electrical conductor. The geometric
shapes of the magnetic flux lines produced by
moving charge carriers (electric current) are
similar to the shapes of the flux lines in an electrostatic field. But there are differences in the ways electrostatic and
magnetic fields interact with the environment.
Electrostatic flux is impeded or blocked by metallic
objects. Magnetic flux passes through most metals with little or no effect,
with certain exceptions, notably iron and nickel. These two metals, and alloys and
mixtures
containing them, are known as ferromagnetic materials because they
concentrate
magnetic lines of flux. An electromagnet provides a good
example.
An air-core
coil carrying direct current produces
a magnetic field. If an iron core is substituted for the air core in
a given coil, the intensity of the magnetic field is greatly increased in the immediate
vicinity of the
coil. If the coil has many turns and carries a large current, and if
the core material has exceptional ferromagnetic properties, the flux
density near the ends
of the core (the poles of the magnet) can be such that the electromagnet
can be used to
pick up and move cars.
When charge carriers are accelerated (as opposed to moving
at constant
velocity), a fluctuating magnetic field is produced. This generates a
fluctuating electric field, which in turn produces another varying magnetic
field. The result is
a "leapfrog" effect, in which both fields can propagate over vast
distances through space. Such a synergistic field is known as an
electromagnetic field. This
is the phenomenon that makes wireless
communications and broadcasting possible.
| LAST UPDATED: |
17 Apr 2001
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