Physics - Current Electricity Question with Solution | TestHub

Consider small volume element between $r$ and $r+dr$
Resistance of this volume along rational directions,
$dR=\frac{\rho dr}{4\pi r^2}$
As all element resistance are in series,
$R=\in t_{r=a}^{r=b}\frac{\rho dr}{4\pi r^2}=\frac{\rho }{4\pi }{\left(-\frac{1}{r}\right)}_{r=a}^{r=b}=\frac{\rho }{4\pi }\left(\frac{1}{a}-\frac{1}{b}\right)$