(i) They travel from north pole to a south pole outside the magnet and south pole to north pole inside the magnet.
(ii) They are closed and continuous curves.
(iii) Two magnetic field lines never intersect each other. If the lines intersect, then at the point of intersection there would be two directions (the needle would point towards two directions) for the same magnetic field, which is not possible.
(iv) The number of field lines per unit area is the measure of the strength of magnetic field, which is maximum at poles. The magnetic field is strong, where the field lines are close together and weak where the lines are far apart.
