A storm cloud sits 2 km above the ground, and the lower surface of the cloud spans about 2 km^2. Treating the cloud and the ground beneath it as a parallel-plate capacitor with C0 = epsilon_0 A / d, what is the approximate capacitance of this cloud-Earth system?

1. Treat the cloud's underside and the ground as the two plates of a capacitor, with A = 2 km^2 = 2 x 10^6 m^2 and d = 2 km = 2000 m. 2. C0 = epsilon_0 A / d = (8.85 x 10^-12 F/m)(2 x 10^6 m^2) / (2000 m). 3. This works out to 8.85 x 10^-9 F, which rounds to 9 x 10^-9 F. 4. A storm cloud is like a giant capacitor precisely because it splits into two oppositely charged regions, the cloud base and the ground, separated by an insulating layer of air. _Source: OpenStax Physics (CC BY 4.0), Ch 18 "Static Electricity", section 18.5 Capacitors and Dielectrics_