Calculation of the Magnetic Forces Between Planar Spiral. See Magnetic Forces and Fields for a discussion on this. Magnetic Force Calculation between Magnets and Coils coil the magnetic field. A similar application of the magnetic field distribution created by Helmholtz coils is found in a magnetic bottle that can temporarily trap charged particles. Helmholtz coils typically have loops with equal radii with current flowing in the same direction to have a strong uniform field at the midpoint between the loops.
