Ans. The secondary circuit.
Ques. What names are given respectively to the currents in circuits 1 and 2?
Ans. The primary and secondary or induced currents.
Primary Induction Coils.—These represent the simplest form of coil, and are used chiefly in low tension ignition to intensify the spark when a battery forms the current source.
A primary coil consists of a long iron core wound with a considerable length of low resistance insulated copper wire, the length of the core and the number of turns of the insulated wire winding determining the efficiency. The effect of the iron core is to increase the self-induction.
The spark produced, as previously explained, is due to self-induction, and it should be remembered that in the operation of the coil, the spark occurs at the instant of breaking the circuit, not at the instant of making.
Secondary Induction Coils.—The arrangement shown in fig. 137, may be considered as a very simple or rudimentary form of secondary induction coil. In the actual coil, the primary and secondary circuits (corresponding to 1 and 2 in fig. 135) are made up of coils of insulated wire, as shown in fig. 143, the primary coil P, being wound over a core C and the secondary coil S being wound over the primary.
The one property of such an arrangement that makes it of great value for most purposes is that the voltage of the induced currents may be increased or diminished to any extent depending on the relation between the number of turns in the primary and secondary winding.
This relation may be expressed in the following rule: