FIG. 21. Diagram of Induction Coil.
Likewise at every "break" in the circuit caused by the interrupter, the lines of force disappear and a second current impulse is induced in the secondary coil. As the number of lines of magnetic force created and destroyed at each make and break is the same, the two electromotive impulses in the secondary are equal. By adding a condenser, however, the current at "make" is caused to take a considerable fraction of time to grow, while at "break" the cessation is instantaneous in comparison. The rate of "cutting" of the lines of force is very much more rapid at "break" than at "make" therefore. The currents at "break" manifest themselves as a brilliant torrent of sparks between the ends of the secondary wires when they are brought near enough together.
The central iron core around which the coils are wound is for the purpose of increasing or concentrating the number of lines of force that pass through the coils. Magnetic lines flow more easily through iron than through air and so prefer that path. It is made up of a bundle of fine iron wires in order to avoid induced currents which would be set up in the iron were it a solid mass and so retard its rapidity of magnetization or demagnetization as to hamper the efficiency of the coil.
LESSON EIGHT. THE PRINCIPLE OF THE TRANSFORMER.
The transformer is a device for raising or lowering A the electromotive force of an alternating current. In principle it consists of two insulated coils of wire called the primary and the secondary wound around an iron ring as shown in the illustration.
FIG. 22. Diagram showing the principle of a Transformer.
If the primary coil is connected to a source of alternating current it will rapidly magnetize and demagnetize the iron ring. The magnetic lines thus created will pass through the secondary coils setting up induced currents.
The ratio of the electro-motive force of the induced current to that of the primary current is in direct proportion to the ratio of the number of turns in the two coils. For example, if the secondary contains twice as many turns as the primary, its electro-motive force will be twice as great.
