A spherical capacitor consists of two thin concentric spherical shells of radii R₁ and R₂. 

(a) Show that the capacitance is given by C = 4πe₀R₁R₂ / (R₂ – R₁).

(b) Show that when the radii of the shells are nearly equal, the capacitance is given approximately by the expression for the capacitance of a parallel-plate capacitor, C = e₀A/d, where A is the area of the sphere and d = R₂ – R₁.