Torque on slowly moving electric or magnetic dipoles in vacuo
The torque on a moving electric or magnetic dipole in slow motion is deduced using the Lorentz transformation of the fields to first order in v/c. It is shown that the obtained equations are independent of the model adopted for the dipole, whether it is of Amperian or Gilbertian type, thus showing the complete validity of the Amp\`ere equivalence principle even in dynamical conditions. The torque is made of three terms: beside that due to the direct torque on the dipole there are two more terms: one due to the torque on the associated perpendicular dual-dipole caused by motion, while the other is the inertial torque due to the displacement of the dipole which carries with it the field linear momentum, or the hidden momentum.
physics.class-ph↗