Ruhmkorff spark coil
Ruhmkorff's coil which is used in this lighter is called also an inductor. It consists of the internal coil L1, made of few windings on the iron core R, connected to the DC current supplier with a fast switch. When the current flows though the coil L1, a magnetic field is created in the core; this field attracts the switch and interrupts the current. With no current the switch is no longer attracted, it returns to its original position and the current flows again.
In this way, the magnetic flux in the core changes continuously. This generates a current in the second coil L2 , with many windings, positioned around the same core. Due to the electromagnetic induction, the electromotive force e is generated in this second coil, proportionally to the velocity of changes of the current I in the first coil.
.The induced voltage is high, thanks to a great number of windings in the second coil and the rapid changes of the current when the circuit is interrupted.
. Similar devices are used in neon lamps, to start the discharge and in the combustion (benzine) engines, for ignition.