Abstract: The relativity between motional and induced electromotive forces is investigated. The reasons are analyzed for the variation in value of total induced electromotive force for different reference frames. A general formula is proposed for calculating the total induced electromotive force under transformation of reference frame. The total induced electromotive forces of rectangular and circular coils moving outside an infinity long wire carries direct current are calculated. The total induced electromotive force measured by the moving observer is equal to the sum of the electromotive forces measured at different positions of the conductor with different times by the stationary observer.

Key words:  induced electromotive force, transformation of reference frame, relativity theory