In fair weather, over flat ground, there may be a downward electric field of 155 N/C.
(a) Assume that the Earth is a conducting sphere with charge on its surface. If the electric field just outside is 155 N/C pointing radially inward, calculate the total charge on the Earth and the charge per unit area.
(b) At an altitude of 240 m above the Earth's surface, the field is only 125 N/C. Calculate the charge density of the air (assumed constant).