Capacitance C = $\frac{Q}{V}$ where Q is the charge on one plate and V is the potential difference between the plates. SI unit: farad (F) = $\frac{C}{V}$. Dimensional formula: [M^(-1) L^(-2) $T^4$ $A^2$]. Capacitance depends only on geometry and dielectric, not on Q or V. Parallel plate capacitor: C = $epsilon_0$A/d where A is the area of overlap and d is the plate separation. For Earth (R ~ 6400 km): C = 4pi*$epsilon_0$*R ~ 711 uF, showing 1 F is enormous. Practical values: pF to mF. A capacitor stores charge and energy by maintaining a potential difference. The electric field between parallel plates is uniform: E = $\frac{sigma}{epsilon_0}$ = $\frac{V}{d}$. Edge effects (fringing fields) are neglected in the ideal parallel plate model.