1. The problem statement, all variables and given/known data (sorry for possible notation errors, that might arise during the translation) Why an electric current passing through a closed loop, can be defined only in stationary conditions? 2. Relevant equations 3. The attempt at a solution I think that the reason is that, if the current is not stationary we must consider also displacement current and the tyme varying electric field, but the question is really generic so I have my doubts. Can you help me? Many thanks!