Section 12 - Electrical System

Section 12
A knowledge of electricity is of great value to service men in working on the electrical units of an automobile, because it enables them to grasp more clearly the operating principles of the various units comprising the electric starting, lighting and ignition systems on Chevrolet cars and trucks.
If service men will carefully study the few simple principles of electricity and magnetism out­lined in the following pages, they will better under­stand the function, operation, testing and repair of the electrical system as explained in this chapter.
Magnetism is the property some bodies have to attract iron and steel, and those bodies having this property are called magnets.
Magnetism was first discovered in the form of magnetic iron ore, known as magnetite. It was found that pieces of this iron ore would stick to­gether, and that if a piece of this ore was suspended by a thread, it would always come to rest with one end pointing in the direction of the magnetic north pole and the other end pointing toward the south pole.
It was found that by bringing the north ends of two of these natural magnets toward each other, there was a decided repelling action between them. The same was true when the two south ends were brought together. However, when the north end of one magnet was brought toward the south end of
out this principle the operation of most electrical machines would be impossible.
Further experiments proved that if a piece of steel was rubbed with a natural magnet, it acquired all of the properties of the natural magnet, without in any way affecting the strength of the natural magnet. In trying this experiment with a piece of iron it was discovered that while the natural mag­net was in contact with the iron, it possessed the properties of a magnet, but the instant the natural magnet was removed from the piece of iron, it lost all of its magnetic properties. From these experi­ments it was proved that steel and iron could be magnetized, and that steel retains magnetism while iron would lose its magnetic properties very readily.
Another experiment used was to lay a piece of paper over a magnet and sprinkle iron filings over the paper. The iron filings will arrange themselves in arcs about the magnets as shown in Fig. 1.
From these experiments certain deductions were made. First, that there is a field of force about every magnet. This field of force is known as the lines of force and is present about all magnets. We do not know in what direction these lines of force travel, but to develop the use of magnetism a rule has to be established. This rule is-"the lines of force of a magnet flow from the south to the north inside of the magnet and from the north to the south outside the magnet," as shown in Fig. 2. This is another important rule to learn about magnetism.
Fig. 1- Lines of Force
another magnet, there was a decided attraction. This proved that like poles repel each other and that unlike poles attract each other. This is one of the most important laws of magnetism, and with-
Fig. 2-Direction of Lines of Force
Lines of force will always follow a conductor of magnetism where they possibly can. Magnetic conductors are-iron, steel, nickel and cobalt.





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