A material of resistivity $\rho$ is formed into a solid, truncated cone of height $h$ and radii $r_{1}$ and $r_{2}$ at either end (Fig. $\mathbf{P 2 5 . 5 9}$ ). (a) Calculate the resistance of the cone between the two flat end faces. (Hint: Imagine slicing the cone into very many thin disks, and calculate the resistance of one such disk.)
(b) Show that your result agrees with Eq. (25.10) when $r_{1}=r_{2}$