Why is a coil behaving different in DC and AC? (the formula Z=omega*L shows that it is like a short in DC and has a frequency growing resistance in AC) But how about the curent through wire (supposing there's no core in the coil)? Why is it proportional to the derivative of the voltage applied? If I place a coil at the output of a DC source do i shortcircuit the outputs and probably destroy the source?