# All magnetic effects, simply provided by a contracted electric field?

Is the contracted electric field of constantly moving charge is what we call a magnetic field? Does the charge, that moves in a straight line has a north and south poles? Contracted electric field has density advantages in the direction perpendicular the moving, is that a north and south?

So give a straight answer - Is the contracted electric field of constantly moving charge is what we call a magnetic field, or there happens something more, with moving charge, except electric field contraction?

• Where did you get that picture? The electric field of a uniformly moving charge is contracted, yes, but symmetrically back to front. It doesn't "pile up" in front at all. – knzhou Sep 13 '18 at 18:26
• @knzhou, one of the questions. The guys there actually answered that it is wrong. Or not completely wrong - it should be mirrored, I didn't understand. – user205695 Sep 13 '18 at 18:29

The distinction between force and field is important because force implies a massive particle on which the force is acting. Therefore there is always a unique rest frame for that particle that you can transform to. A field has no such well defined rest frame and some fields (eg a plane wave) have no corresponding sources. Additionally, $E^2-B^2$ is an invariant, so in fields where this quantity is negative there is no frame where the magnetic field is 0 despite the fact that there is a frame where the magnetic force is 0.