Two particles, each of mass m and charge q, are attached to the two ends of a massless rigid rod of length 2R. The rod is rotated at constant angular speed about a perpendicular axis passing through its centre. The ratio of the magnitudes of the magnetic moment of the system and its angular momentum about the centre of the rod is :

A magnetic substance has susceptibility –0.05 at 300 K. The magnetic susceptibility of the substance at 600 K will be :