Problem 3.203

The radii of spherical capacitor electrodes are equal to $a$ and $b,$ with $a< b .$ The interelectrode space is filled with homogeneous substance of permittivity $\varepsilon$ and resistivity $\rho .$ Initially the capacitor is not charged. At the moment $t=0$ the internal electrode gets a charge $q_{0}$. Find: (a) the time variation of the charge on the internal electrode; (b) the amount of heat generated during the spreading of the charge.