# Energy creation in a moving solenoid - Physics > Classical Physics

Abstract: The electromagnetic energy $U {em}$ stored in the magnetic field of an idealsolenoid at rest appears for a moving observer as $U- {em}$, a sum of magneticand electric energies satisfying: $U- {em} > \gamma U {em}$. We explain thisseemingly paradoxical result calculating the stresses in the solenoid structureand showing that the total energy of the solenoid transforms by the expectedrelativistic factor $\gamma$.

Author: Nelson R. F. Braga, Ranieri V. Nery

Source: https://arxiv.org/