Physics Question from JEE Main 2023 · 31 January, Shift 1

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