Question related to electromagnetic theory

[uzair_ha91]

Question:
A circuit contains an iron cored inductor, a switch and a DC source arranged in series. The switch is closed and after an interval reopened. Explain why a spark jumps across the switch contacts.
Attempt:
I guess it's related to self induction and back emf but am unable to understand how a spark can be produced in such a case...

 

[lanedance]

on the right track, to produce an electrical arc, you first need quite a large voltage...

thinking about what's going on, before opening the switch you have a steady flow of current through the inductor, which produces a magnetic field

when you open the switch you immediately intererupt the current & so the magnetic field...

can you find any equations to help explain what is going on...