\[\begin {array} {1 1} (a)\;\frac{\mu _0 iv}{2 \pi x} \bigg(\frac{1+b}{b}\bigg) & \quad (b)\;\frac{\mu_o i^2 v}{4 \pi ^2 x} \log \bigg(\frac{b}{l}\bigg) \\ (c)\;\frac{\mu_0 ilbv}{2 \pi x(l+x)} & \quad (d)\;\frac{\mu_0 ilbv}{2 \pi x (l+x)} \end {array}\]