Magnetics

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

(Given : Permeability of vacuum \(\mu_{0}=4 \pi \times 10^{-7} \mathrm{NA}^{-2}\))