Just want a quick simple question answered. Say if I have a charge density as seen in frame and they want me to find the charge density and charge current density as seen in frame .
I haven't been given the charge current density as seen in frame so my question is, for my four-current vector can I just set the three current to the zero vector, i.e. setting the frame as the rest frame for the three current so that it sees the three current as (0,0,0) relative to that frame if this makes sense? Can I always do this?
And actually passed?