(a) A spherical metal shell is charged to an electrostatic potential V . Cut this shell in half and pull the halves infinitesimally apart. Find the force with which one hemisphere of the shell repels the other hemisphere.
(b) A spherical capacitor is formed from concentric metal shells with charges ±Q and radii b > a. Cut this capacitor in half and pull the halves infinitesimally apart. Find the force with which the two halves repel one another.