1942 - 1947 CHEVROLET SHOP MANUAL
Section 12 - Electrical System
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12-2
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Permanent magnets are made of hard steel and
hold their magnetism almost
indefinitely. However,
their use is somewhat limited because one cannot
change their strength at will and,
this being the case, it is
impossible to control them. On the automobile permanent magnets are
used in the speedometer and ammeter, as both of these
instruments are measuring devices.
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lated wire, as shown in Fig. 3. When this device
is connected with a source of
electrical energy, the
core becomes magnetized and possesses all of the
properties found in both natural
and permanent magnets. To
explain the reason for this iron core
becoming magnetized it will be
necessary to show the
magnetic properties of the electrical circuit.
Every current-carrying conductor has a magnetic
field surrounding it. The magnetic field always
travels in a clockwise direction
around the conductor, looking in the direction in which the current
flows. In Fig. 4, the arrow indicates the direction of current flow
through the wire or conductor,
and looking along the wire from
the end at which the current enters, the magnetic field is
found to be traveling in a
clockwise direction around it.
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Fig. 5-Polarity of Electro Magnet
In order to determine
the polarity of the electro
magnet shown in Fig. 5, the following rules are
used:
1. Direct
current flows through its circuit from positive to negative.
2. The
magnetic field about a current-carrying
conductor always travels in a
clockwise direction about
the conductor, looking in the direction
in which the current is flowing.
3. Lines
of force always follow a conductor of
magnetism where they possibly
can.
4. Lines
of force always flow from the south to
the north inside the magnet and
from north to south
outside of the magnet.
By referring to Fig.
5, it will be noted that the
current flowing from the positive of the battery passes around the
core of the magnet and back to the negative of the battery. The
magnetic field surrounding the wire is traveling clockwise around the
wire, and in so doing engages the core while it is
traveling upward and follows the
iron core. The lines of force emerging from the top of the magnet
form a north pole and where they re-enter the
core form the south pole.
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Fig. 3-Electro Magnet
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ELECTRO MAGNETS
Electro magnets are made up of an iron core over which is wound a
number of turns of insu-
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Fig. 4-Direction of Lines of Force about
Conductor
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