For a single-phase, two-wire line consisting of two solid cylindrical conductors of same radius, \(r\), the total circuit inductance, also called loop inductance, is given by (in \(\mathrm{H} / \mathrm{m}\) )

(a) \(2 \times 10^{-7} \ln \left(\frac{\mathrm{D}}{r^{\prime}}ight)\)

(b) \(4 \times 10^{-7} \ln \left(\frac{\mathrm{D}}{r^{\prime}}ight)\)

where \(r^{\prime}=e^{-\frac{1}{4}} r=0.778 r\)