Two bar magnets A and B are geometrically similar but the magnetic moment of $A$ is twice that of $B$. $T_1$ is the time period of oscillation when their like poles are kept together. When unlike poles are kept together, the time period of oscillation is $T_2$. The ratio $T_1: T_2$ will be

The magnetic susceptibility of iron is 5499 . The relative permeability of iron will be

If $M$ is the magnetisation induced in the material, H is the magnetic field intensity, B is the net magnetic field inside the material then the correct relation between them is ( $\mu_0=$ permeability of free space)