Principles of Induction Coil.
a. Comparison with transformer. The induction coil is essentially a transformer. This similarity may be noted
by comparing the circuit diagrams of the transformer and induction coil in figure 36. Electrically, the action of an
induction coil is the same as that of a transformer, and the same basic principles apply to it. The transformer in its
simplest form consists of two conducting coils which have mutual inductance between them. The common connection
between the windings of the induction coil does not affect the mutual inductance between the coils. As a result of the
mutual inductance, a varying current in one winding induces an ac voltage in the other. The value of the induced ac
voltage depends on the turns ratio and on the rate at which the current changes: the higher the rate of change, the greater
the induced voltage. The induced voltage has the waveshape of the changing current. This action of the transformer is
explained in detail in TM 11-681.
FIGURE 36. Comparison of Transformer
and Induction Coil.