Basic Electrical Theory
MAGNETISM
Electromagnetism
The relationship between magnetism and electrical current was discovered by a Danish scientist
named Oersted in 1819. He found that if an electric current was caused to flow through a
conductor, the conductor produced a magnetic field around that conductor (Figure 21).
Figure 21 The Magnetic Field Produced by Current in a Conductor
Polarity of a Single Conductor
A convenient way to determine the relationship between the current flow through a conductor
and the direction of the magnetic lines of force around the conductor is the left-hand rule for
current carrying conductors, as illustrated in Figure 22. The student should verify that the left-
hand rule holds true for the examples shown in Figure 21.
Figure 22 Left-hand Rule for Current
Carrying Conductors
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