I was trying to understand how an ignition coil circuit works practically, and came upon this website explaining the behavior of an ignition coil when subjected to changes in voltage: http://www.learnabout-electronics.org/ac_theory/inductors.php
Especially the following paragraph:
This voltage will however now be much larger than the original supply voltage; this is because the amplitude of a voltage induced into a conductor is proportional to (among other factors) the rate of change of the magnetic field. At switch on, because there were two opposing voltages changing, the supply increasing and the back e.m.f. decreasing, the rate of change was slowed down. However at switch off there is no supply voltage so the magnetic field collapses extremely quickly causing a very rapid rate of change and therefore producing a very large voltage pulse.
should lead to symmetric behavior when a switch is closed and opened. In fact, according to my understanding, the voltage spike shown in the following graph should be in the other direction, as it would oppose the decrease in current. Am I understanding inductors incorrectly, or is there in practice much more to the topic which simple EE theory does not cover?