學院物理/電流與電阻

同軸電纜的電阻

$\begin{array}{cc}& R=\int dR=\int \frac{\sigma dr}{a}=\int \frac{\sigma dr}{2\pi rL}\\ & =\frac{\sigma }{2\pi rL}\underset{b}{\overset{a}{\int }}\frac{dr}{r}=\frac{\sigma }{2\pi rL}\ln \frac{b}{a}\end{array}$