MAGNETISM
Magnetism can be used to produce electricity and
electricity can be used to produce magnetism.
Much about magnetism cannot be explained by our
present knowledge. However, there are certain pat-
terns of behavior that are known. Application of these
behavior patterns has led to the development of gen-
erators, motors and numerous other devices that uti-
lize magnetism to produce and use electrical energy.
See Figure 1. The space surrounding a magnet is per-
meated by magnetic lines of force called “flux”. These
lines of force are concentrated at the magnet's north
and south poles. They are directed away from the
magnet at its north pole, travel in a loop and re-enter
the magnet at its south pole. The lines of force form
definite patterns which vary in intensity depending on
the strength of the magnet. The lines of force never
cross one another. The area surrounding a magnet in
which its lines of force are effective is called a “mag-
netic field”.
Like poles of a magnet repel each other, while unlike
poles attract each other.
Figure 1. Magnetic Lines of Force
ELECTROMAGNETIC FIELDS
All conductors through which an electric current is
flowing have a magnetic field surrounding them. This
field is always at right angles to the conductor. If a
compass is placed near the conductor, the compass
needle will move to a right angle with the conductor.
The following rules apply:
• The greater thecurrentflow throughtheconductor,
the stronger the magnetic field around the conductor.
• The increase in the number of lines of force is
directly proportional to the increase in current flow
and the field is distributed along the full length of
the conductor.
• Thedirectionofthelinesofforcearoundaconduc-
tor can be determined by what is called the “right
hand rule”. To apply this rule, place your right hand
around the conductor with the thumb pointing in
the direction of current flow. The fingers will then be
pointing in the direction of the lines of force.
NOTE: The “right hand rule” is based on the “cur-
rent flow” theory which assumes that current
flows from positive to negative. This is opposite
the “electron” theory, which states that current
flows from negative to positive.
Figure 2. The Right Hand Rule
ELECTROMAGNETIC INDUCTION
An electromotive force (EMF) or voltage can be pro-
duced in a conductor by moving the conductor so that
it cuts across the lines of force of a magnetic field.
Similarly, if the magnetic lines of force are moved so
that they cut across a conductor, an EMF (voltage)
will be produced in the conductor. This is the basic
principal of the revolving field generator.
Figure 3, below, illustrates a simple revolving field
generator. The permanent magnet (Rotor) is rotated
so that its lines of magnetic force cut across a coil of
wires called a Stator. A voltage is then induced into
the Stator windings. If the Stator circuit is completed
by connecting a load (such as a light bulb), current
will flow in the circuit and the bulb will light.
Figure 3. A Simple Revolving Field Generator
Page 10
PART 1
GENERAL INFORMATION
SECTION 1.1
GENERATOR FUNDAMENTALS
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