In fair weather, over flat ground, there is a downward electric field of about 150 N/C.
(a) Assume that the Earth is a conducting sphere with charge on its surface. If the electric field just outside is 150 N/C pointing radially inward, calculate the total charge on the Earth and the charge per unit area.
(b) At an altitude of 250 m above Earth's surface, the field is only 120 N/C. Calculate the charge density (charge per unit volume) of the air (assumed constant).