Hardware Reference
In-Depth Information
ally flow from negative to positive, as shown in the figure, although we normally think of
current flowing in the other direction.
Figure 8.1
A magnetic field is generated around a wire when current is passed through it.
Electromagnetism was discovered in 1819 by Danish physicist Hans Christian Oersted,
when he found that a compass needle would deflect away from pointing north when
brought near a wire conducting an electric current. When the current was shut off, the
compass needle resumed its alignment with the Earth's magnetic field and again pointed
north.
The magnetic field generated by a wire conductor can exert an influence on magnetic ma-
terial inthefield.Whenthedirection oftheflowofelectric currentorpolarityisreversed,
the magnetic field's polarity also is reversed. For example, an electric motor uses electro-
magnetism to exert pushing and pulling forces on magnets attached to a rotating shaft.
Another effect of electromagnetism was discovered by Michael Faraday in 1831. He
found that if a conductor is passed through a moving magnetic field, an electrical current
is generated. As the polarity of the magnetic field changes, so does the direction of the
electric current's flow (see
Figure 8.2
).
Figure 8.2
Current is induced in a wire when passed through a magnetic field.
