En and Ec are the non-conservative and conservative electric field respectively. I've quoted this from the textbook I'm using (University Physics by Young and Freedman 12th edition). Now, it seems to me that the author just invoked the assumption that the inductor have negligible resistance and hence it only needs very small electric field (thus approximately zero?) to move the charges through it out of nowhere. It seems wishy-washy to me, it's very convenient so that we can just advance through the discussion and go ahead with the derivation and come up with a very nice equation. My question is, really, how come the net electric field within an inductor is zero? The proposition that 'the inductor just have a very very small resistance so the electric field is zero' isn't very convincing to me, can anyone expound on this for me?