Hi I am confused about rotating magnet. Feynman lectures on physics 13–6 The relativity of magnetic and electric fields, http://www.feynmanlectures.caltech.edu/II_13.html , deals with two inertial frames. Wire is charged in some inertial frame. Can we apply it to tangential parts of curved wire rings as part of an electromagnet? I wonder whether electromagnet is charged with rotation.