Magnetic field (Question 1 (8 Marks)) — UPSC Physics Optional IFoS 2022 Paper I

A long straight wire of circular cross-section is made of non-magnetic material (\chi_{\text{m}} = 1^\circ to a good degree of approximation). It is of radius a. The wire carries a current I which is uniformly distributed over its cross-section. Compute the energy per unit length stored in the magnetic field contained within the wire.