The inductor below is conducting an arbitrary current, with the switch on. Suddenly the switch is set off and and voltage over the inductor raises to the negative infinity according to Vl = L*di/dt However, voltage is defined as energy per charge. V=J/C The energy stored "in" the inductor is finit and El = L*i^2/2 Combining these equations, would the voltage instead then raise to Vl = L*i^2/(2*C) ? Where C is the sum of all free charges or something, relevant for the equation? I guess what I've wrote above is far to simplified to describe what would happen, but let's consider this thought experiment also. Imagine that there are only two relevant charges in the whole system. When the current is switched off, this would get an infinite potential energy distributed on a finite number of charge. This would thus have inifinite energy created out of a finite amount of energy, thus the Vl=Ldi/dt model must begin to show serious flaws at some point? EDIT: And no we don't consider things such as parasitic capacitance, eddy current or anything like that here.