There is some confusion as to what the principle fields in electromagnetics are and what the derived fields are. In the force(Lorentz) equation we see that the force is equal to the charge of the particle times the electric field (E) plus the charge times the particles velocity crossed with the magnetic induction (B). The confusion arises from the way that the equations for the D and B field are written: it seems that B field is to be paired with D and E with H. The truth is that to maintain Lorentz invariance, sildenafil the force equation must either contain D and H or E and B. That is to say, the force shouldn’t change depending on which direction the system moves. To accomplish this, the Lorentz force equation must contain either E and B fields or the D and H fields. Then do we use he E and B field or D and H field? D and H fields are computational aids; these fields do not exist in the microscopic world. B and E fields do, which is why they are the principle electromagnetic fields (the concepts of current or charge density do not exist on the quantum level).