Abstract

The applicable ranges of the principle of relativity were reconsidered. There are magnetic field forces between positive charge and negative charge in an electric doublet which is moving in a laboratory reference frame, whereas, analyzing the electric doublet with the same physical method in a reference frame which is at rest relative to the electric doublet, no magnetic field force exists between the two charges. The results obtained in the two frames are self-contradictory. Maxwell’s equations maintain the form invariant under Lorentz transformation can not fully prove that electromagnetism laws satisfy requirement of the principle of relativity, because the form invariant are the same as the expression for Doppler effect.

Key words: The principle of relativity, applicable range, inertial reference frame, magnetic field force, Maxwell’s equations.