Hi forum Can anyone explain where the energy is .... Consider a railigun, a voltage is put across the two parallel rails, a current starts building up, whille some energy is stored in the magnetic field inside the current loop. The energy stored in the magnetic field is: U=0.5*L*I^2 I being the current and L the self inductance of the loop. As the projectile moves the area of the loop increases. I would expect that the self inductance of the loop then was decreasing, lowering the energy in the magnetic field while accelerating the projectile....but it seems that it is the other way around....(using https://www.eeweb.com/tools/rectangle-loop-inductance to calculate the inductance for different values) Where is the energy coming from ?