Deduce the capacitance an isolated conducting sphere. Then find the capacitance spherical capacitor consisting of two hollow concentric spheres of radii $r_1$ and $r_2\left(r_1>r_2\right).$ Now show that a conducting sphere may be regarded as a spherical capacitor where outer sphere is at infinity.

Two capacitors of capacitance $C_1$ and $C_2$ having charges $Q_1$ and $Q_2$ are joined together with

Two capacitors of capacitance $C_1$ and $C_2$ having charges $Q_1$ and $Q_2$ are joined together with

positive plate of one connected to the negative plate of the other. Find the common potential in the two cases.