There is a mark "N" on the base of the Helmholtz coils that indicate the direction of the magnetic field produced by the coils when current flows through them. Normally when a bar magnet is placed in the Helmholtz coils the bar magnet will oscillate. However, if the mark "N" on the Helmholtz coils POINTS SOUTH, then the bar magnet ROTATES INSTEAD of oscillating when the current is turned on. WHY? Please give a brief answer