1. The problem statement, all variables and given/known data Hi, My professor offered the following question: Is it possible to have an electromagnetic field that appears as a purely electric field in one inertial frame and as a purely magnetic field in some other inertial frame? 2. Relevant equations 3. The attempt at a solution I agree that if there is a point charge at rest there exists only electric field lines. And I also agree that if the charge is put in motion that from the frame of the lab there is an electric and magnetic field but from a frame attached to the charge there is only an electric field. But I can't convince myself there could be one frame where there is only an electric field and another frame in which there is only a magnetic field. Can someone point me in the direction of what I am missing? Is this a qualitative or quantitative issue? Am I oversimplifying this? Thanks in advance!