When an electric circuit is getting opening by a switch, we notice of course that the current stopS.to flow but we can also observe a very brief flash more or less bright depending on circumstances between the metallic separating parts of the switch. This flash, called spark, is the result of a complex phenomenon in which take place simultaneously the burning of metallic particules pulled away from the switch and the ionization of gases situated at this spot and being induced by the electric field existing between the poles of the switch.