Abstract: The relative motion between a bar magnet and a conducting ring is considered to be an example, we firstly discuss the difference of electric and magnetic field in the magnet and the ring reference system. Also, starting from Lorentz force which is the nature of motional emf in the magnet reference system, we deduce Faraday＇s law of induction. Then we directly give the mathematical expression of the property of induced electric field by using the principle of relativity and in-depth discussion of the relation between the electric field and the magnetic field in the ring reference system. Finally, we present and simple analysis different consideration of Einstein and Feynman on this issue.

Key words: principle of relativity, Lorentz force, Faraday＇s law of induction, relativity of electromagnetic fields