Colin you are right that there is always resistance, however small, and that it plays its part.
However the formulae I gave back in post#12 are the result of integrating
\(\frac{R}{L}dt = \frac{{di}}{{I - i}}\)
assuming L to be constant
If L is in fact a function of current (or therefore time) the maths gets rapidly hairy.
L changes because the core susceptibility changes as more magnetic materia in Sgt Wookie's example, l is drawn in, because it is free to do so and mechanically configured to do so.
However the formulae I gave back in post#12 are the result of integrating
\(\frac{R}{L}dt = \frac{{di}}{{I - i}}\)
assuming L to be constant
If L is in fact a function of current (or therefore time) the maths gets rapidly hairy.
L changes because the core susceptibility changes as more magnetic materia in Sgt Wookie's example, l is drawn in, because it is free to do so and mechanically configured to do so.