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The connection between electricity and magnetism was made by Oersted,
a Danish scientist, in 1820. He had frequently demonstrated the
nonexistence of a connection between electricity and magnetism. His
usual procedure was to place a current-carrying wire at right angles
to, and directly over, a compass needle to show that there was no
effect of one on the other. One occasion, at the end of his lecture,
he placed the wire parallel to the compass needle and saw the needle
move to one side. When he reversed the current in the wire, the
needle, to his amazement, deviated in the opposite direction. Thus a
great discovery concerning electromagnetism was made quite by
accident.
There is no actual knowledge as to why some materials have magnetic
properties and others have not. The "electron theory" generally is
accepted as the best explanation of magnetism. It is also known as
the "domain theory."
According to the theory, an electron moving in a fixed circular orbit
around the proton creates a magnetic field with the north pole on one
side of the orbit and a south pole on the other side. It is assumed
that the orbiting electron carries a negative charge of electricity,
which is the same as electrical current flowing through a conductor.
Current flow, then, is from negative to positive. When a number of
magnetized orbiting electrons exist in a material, they interact with
each other and form "domains," or groups of atoms having the same
magnetic polarity. However, these domains are scattered in random
patterns throughout and the material is, in effect, demagnetized.
Under the influence of a strong external magnetic field, domains
become aligned and the total material is magnetized. The strength of
its magnetic field depends on the number of domains that are aligned.
In magnetic substances, the domains align themselves in parallel
planes and in the same direction when placed in a magnetic field.
This arrangement of the electron-created magnets produces a strong
magnetic effect.
If you stroke a piece of hardened steel with a magnet, the piece of
steel itself will become a magnet. (Steel railroad tracks laid in a
north-to-south direction become magnetized because they lie parallel
to the magnetic lines of the earth.) Much stronger magnets and
magnetic fields can be produced by electrical means. Placing a piece
of steel in any strong magnetic field will cause it to become
magnetized.
A magnetized field surrounds any conductor carrying an electrical
current. The discovery of that fact resulted in the development of
much of our electrical equipment. The "field of force" is always at
right angles to the conductor. Since the magnetic force is the only
force known to attract a compass needle, it is obvious that a flow of
electric current produces a magnetic field similar to that produced
by a permanent magnet. Not only is the field of force at right angles
to the conductor, but the field also forms concentric circles about
the conductor. When the current in the conductor increases, the field
of force is increased. Doubling the current will double the strength
of the field of force.
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