Thus, in the secondary circuit is set up a series of currents  alternating in direction, their periodicity depending upon the  rate of interruption of the primary current.  The inductive effect is augmented by the presence of the  iron core, with its alternate magnetisations and demagnetisa-  tions, which are in effect similar to rapid movements of a  strong magnet alternately toward and away from the secondary  windings.     The E.M.F. or voltage of the secondary currents will  depend upon and vary directly as—

1. The number of turns of wire in the coil;

2. The strength of the primary current; and

3. The suddenness of the break of the primary.

The strength, quantity, or amperagre, following Ohm’s  law, will vary directly with those factors, and inversely as  the resistance of the secondary circuit.

1. A very long secondary winding  high E.M.F., with discharge sparks of great length; but its  concomitant high resistance will prevent a great quantity of  current passing, and the sparks will be correspondingly thin  and thready.

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