Q no 32. A long straight wire of circular cross-section is made of a non-magnetic material. The radius of cross-section of the wire is a. The wire carries a current I which is uniformly distributed over its cross-section. The energy stored per unit length in the magnetic field contained within the wire is
(a) $\frac{{\mu }_o{I}^2}{8\mathrm{\pi }}$
(b) $\frac{{\mu }_o{I}^2}{16\mathrm{\pi }}$
(c) $\frac{{\mu }_o{I}^2}{4\mathrm{\pi }}$
(d) $\frac{{\mu }_o{I}^2}{2\mathrm{\pi }}$