1. The problem statement, all variables and given/known data Suppose the magnetic field line pattern is cylindrical symmetric. Explain with Stokes theorem that the field decreases like 1/r (with r the distance from the axis of the cylinder). 2. Relevant equations Stokes theorem 3. The attempt at a solution I was thinking of a circular loop around the axis. The line integral around this loop is B*2*pi*r. But I don't really know what I can say about the curl of B if you only know about the cylindrical symmetry. Thanks in advance for helping me out!!