OPERATION AND CARE OF LOW AND HIGH TENSION MAGNETOS AND MAGNETO IGNITION SYSTEMS
GENERAL PRINCIPLES
The red-painted toy magnet that is one of the properties of childhood and with which everyone is familiar, may well be used as the beginning of a study of the magneto, for with it the characteristics of magnetism may be observed. A little experimenting will show that the magnet will attract, or “pick up”, iron and steel objects only, having no effect on copper, brass, lead, wood, or, for practical purposes, any other substance. Furthermore, it illustrates the fact that when iron and steel are in contact with it, they in turn become magnetic, able also to attract tacks and other bits of the same metals. Iron, however, is shown by experiment to be magnetic only when in actual contact with the magnet, losing its magnetism as soon as the contact is broken, while when steel is magnetized by touching it to a magnet it remains magnetic. This fact is illustrated by the magnet itself, which is of steel and therefore capable of retaining its power for a greater or less time, depending on its quality and hardness.
Fig. 1.
Magnetic
Lines of
Force.
If iron filings are scattered on a piece of paper laid over a magnet they will not fall evenly and regularly, but will collect most thickly at the ends, or poles, of the magnet, showing that there the magnetic attraction is stronger than at any other points. If the filings are examined closely it will be seen that they have taken up definite positions, forming lines and curves extending between the two poles (Fig. 1). This is the simplest method by which the magnetism may be made visible, and it illustrates the fact that the power of a magnet acts in a series of lines passing from one pole to the other. If a piece of iron or steel is placed across the poles of a magnet these lines, or as many of them as possible, will use it as a bridge or conductor, because they can pass through it more easily than through air. Such a piece of iron or steel is called a keeper, and by its use the magnet will retain its strength for a much greater time than if the lines are obliged to make their way through the far greater resistance that the air presents to their passage.
These lines, which are known as magnetic lines of force, always move in the same direction, passing through the air or the keeper from the north pole of the magnet to the south pole, and passing through the metal of the magnet itself from the south pole to the north pole.
The strength of a magnet depends on the number of these lines of magnetic force that it possesses. If two magnets, one strong and the other weak, are placed under sheets of paper on which iron filings are scattered, their comparative strengths are clearly shown by the difference in the number of lines of force that the filings show them to possess.
The space through which a magnet makes itself felt is known as the magnetic field, and this is large or small, according to the number of lines of force. The stronger the magnet, the larger will be the sweep of the curves of its lines of force, and the greater will be the field that they form.