For 10 points, identify this counterpart to the electric field, with strength measured in Teslas or Gauss.
Because it is divergence-free, the curl of its vector potential can be used in the Lorentz Force equation, where it is crossed with velocity, and they do not do any work on objects that move through them. The Hall effect can be used to find the sign of the charge carriers when a current flows in one of these. Biot-Savart's law describes the magnitude of these, and its line integral is proportion to the current according to Ampere's Law. For 10 points, identify this counterpart to the electric field, with strength measured in Teslas or Gauss.
Because it is divergence-free, the curl of its vector potential can be used in the Lorentz Force equation, where it is crossed with velocity, and they do not do any work on objects that move through them.
{magnetic fields}