Hello friends, A while back I raised the similar question regarding absolute nature of Magnetic force due to a current carrying wire on a moving charge. But supposedly I was shown to be incorrect. Since, Magnetic filed is a relativistic effect, then every magnetic force should be compatible with Principle of relativity ! right ? But consider a simple example of a charge moving along a current carrying wire. Does it matter which one is moving, or is it the relative motion only which counts (according to Principle of relativity). 1.) current carrying wire and charge are at rest relative to each other and the charge starts moving along the wire. 2.) current carrying wire and charge are at rest relative to each other and this time it is the the current carrying wire which start moving along its length. Now, I know, that there will be a magnetic force in scenario (1), but I think there will be NO magnetic force (of-course on the charge ) in the scenario (2). Above preference that there will be force only when the charge will move, says Principle of relative motion does not apply to Magnetic force from a current carrying wire and a charge. Since according to Principle of relativity, the magnetic field and therefore force should depend only on relative motion !! And guys, don't explain the relative nature of magnetic field using the Faraday's law of induction i.e. magnet and conductor problem, since this question is about the ampere's law for magnetism.