I am studying Griffiths and I have the following doubt. For the multipole expansion of the magnetic vector potential Griffiths simply writes the formula for a loop of wire and then ofcourse
is 0 around a loop (eq 5.78 and 5.80) and then he concludes that there is no monopole, but think about a finite segment of line charge that is moving at v(<<c) in that case the integral will not be a closed one, how do we then account for the fact that there are no monopoles then? Also why has he put a closed integral in the first place?