A rod with circular cross-section area 2 cm^2 and length 40 cm is wound uniformly with 400 turns of an insulated wire. If a current of 0.4 A flows in…

A rod with circular cross-section area $\displaystyle 2 \mathrm{~cm}^2$ and length $\displaystyle 40$ cm is wound uniformly with $\displaystyle 400$ turns of an insulated wire. If a current of $\displaystyle 0.4$ A flows in the wire windings, the total magnetic flux produced inside windings is $\displaystyle 4 \pi \times 10^{-6} \mathrm{~Wb}$. The relative permeability of the rod is (Given : Permeability of vacuum $\displaystyle \mu_0=4 \pi \times 10^{-7} \mathrm{NA}^{-2}$ )