Spherical capacitor (inner radius a, outer radius b): C = 4pi$epsilon_0$$\frac{ab}{b-a}$. As b -> infinity (isolated sphere): C = 4pi*$epsilon_0$a. As (b-a) -> 0 with b ~ a ~ R: C ~ 4pi*$epsilon_0$R^$\frac{2}{b-a}$ = $epsilon_0$A/d (reduces to parallel plate, since A = 4pi$R^2$ and d = b-a). Cylindrical capacitor (inner a, outer b, length L): C = 2pi$epsilon_0$L/ln$\frac{b}{a}$. For (b-a) << a, this also reduces to the parallel plate formula with A = 2piaL. These are derived by finding V from E (using Gauss's law) and applying C = $\frac{Q}{V}$. JEE problems may involve concentric spherical or coaxial cylindrical configurations with multiple dielectric layers.