Consider the Earth and a cloud layer 800 m above the planet to be the plates of a parallel-plate capacitor.
a) If the cloud layer has an area of 3.0 km2 = 3000000 m2, what is the capacitance?
(b) If an electric field strength greater than 3.0 x 106 N/C causes the air to break down and conduct charge (lightning), what is the maximum charge the cloud can hold?