Regard the Earth and a cloud layer 673 m above the Earth as the "plates" of a capacitor.

Regard the Earth and a cloud layer 673 m above the Earth as the "plates" of a capacitor. Assume that the cloud layer has an area of 1 km2, that the air is pure and dry, and that charge builds up until a maximum electric field of 2.58x106 N/C builds up between the "plates". What is the maximum charge (in C) that the cloud can hold?