THE STABLE CONFIGURATIONS OF A FINITE SIZE NAIL IN A MAGNETIC FIELD AND THE PHASE TRANSITION

The standing and tumbling of a nail in a magnetic field is a daily phenomena, We calculated potentials of the finite size nail in the fields of a infinite long wire, the parallel infinite long wires and the circular current loop, respectively. The stable points of the potential determine the stable configurations of the nail. Involved in the intrinsic magnetic moment of the nail, the standing point of nail will change from a meta-stable point to a unstable point while moving in the magnetic field, then tumbling down. Landau theory of phase transition can be used to analyze the stable configuration of the nail. The numerical results shows that the critical index are exactly consistent with the prediction of Landau theory. making the standing and tumbling of a nail to be a perfect model of Landau theory. It is very charming that the abstract concept in theoretical physics are demonstrated in a simple classical phenomena.