66 Electromagnetism
In the spring of 1820, Hans Oersted was giving a lecture to one of his classes when an
amazing thing happened. He made a grand discovery—the only major scientific discovery
made in front of a class of students. It was a simple demonstration for graduate-level students of how electric current heats a platinum wire. Oersted had not focused his research on
either electricity or magnetism. Neither was of particular interest to him. Still, he happened
to have a needle magnet (a compass needle) nearby on the table when he conducted his
demonstration.
As soon as Oersted connected battery power to his wire, the compass needle twitched
and twisted to point perpendicular to the platinum wire. When he disconnected the battery,
the needle drifted back to its original position.
Each time he ran an electric current through that platinum wire, the needle snapped
back to its perpendicular position. Oersted’s students were fascinated. Oersted seemed flustered and shifted the talk to another topic.
Oersted did not return to this amazing occurrence for three months—until the summer
of 1820. He then began a series of experiments to discover if his electric current created a
force that attracted the compass needle, or repelled it. He also wanted to try to relate this
strange force to Urkraft.
He moved the wire above, beside, and below the compass needle. He reversed the current
through his platinum wire. He tried two wires instead of one. With every change in the wire and
current, he watched for the effect these changes would produce on the compass needle.
Oersted finally realized his electric current created both an attractive and a repulsive force
at the same time. After months of study, he concluded that an electric current created a magnetic
force and that this force was a whole new type of force—radically different than any of the
forces Newton had described. This force acted not along straight lines, but in a circle around the
wire carrying an electric current. Clearly, he wrote, wires carrying an electric current showed
magnetic properties. The concept of electromagnetism had been discovered.
Fun Facts: The aurora borealis, or “northern lights,” are an electromagnetic phenomenon, caused when electrically charged solar particles collide with Earth’s magnetic field. In the Southern hemisphere these
waving curtains of light form around the south pole and are called the aurora australis, or “southern lights.”
More to Explore
Beaumont, LeIonce. Memoir of Oersted. Washington, DC: Smithsonian Institution, 1997.
Brain, R. M., ed. Hans Christian Oersted and the Romantic Quest for Unity. New
York: Springer, 2006.
Cohen, Bernard. Revolutions in Science. Cambridge, MA: Harvard University Press,
1995.
Dibner, Bern. Oersted and the Discovery of Electromagnetism. Cambridge, MA:
Burndy Library, 1995.
Oersted, Hans. The Discovery of Electromagnetism Made in the Year 1820. London:
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