This section has a list of the basic formulas of electromagnetism, given in the SI, Heaviside–Lorentz, and Gaussian systems. Here E and D are the electric field and displacement field, respectively, B and H are the magnetic fields, P is the polarization density, M is the magnetization, ρ is charge density, J is current density, c is the speed of light in vacuum, ϕ is the electric potential, A is the magnetic vector potential, F is the Lorentz force acting on a body of charge q and velocity v, ε is the permittivity, χ e is the electric susceptibility, μ is the magnetic permeability, and χ m is the magnetic susceptibility.