The total inductance \(L_{\mathrm{P}}\) of a solid cylindrical conductor (of radius \(r\) ) due to both internal and external flux linkages out of distance \(\mathrm{D}\) is given by (in \(\mathrm{H} / \mathrm{m}\) )

(a) \(2 \times 10^{-7}\)

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

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

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