Switched infinite-wire retarded potential
= Switched infinite-wire retarded potential
For a spatially uniform line current $I\Theta(t)$, the causal potential outside the line is $A_z=(\mu_0I/2\pi)\operatorname{arcosh}(ct/r)$ for $ct>r$, and zero before arrival. The finite causal integration length makes it finite at finite time, unlike an absolute magnetostatic potential for an infinite wire.