The Earth itself is a relatively good conductor. The atmosphere near the surface of the Earth, the troposphere and stratosphere, is composed mainly of neutral oxygen and nitrogen molecules, and it is a fairly good insulator.
About 30 km above the surface of the Earth, the atmosphere is composed mainly of ions. These ions are created by the bombardment of cosmic rays, and the low density of gas at that height inhibits their recombining to form neutral species. This portion of the atmosphere, called the ionosphere, is a good conductor. (See figure.)
Thus, a very much simplified model of the Earth and its atmosphere consists of two conductors separated by an insulator. Furthermore, there is a net charge of –106 C on the surface of the Earth and a corresponding positive charge on the ionosphere. The potential between the Earth's surface and the ionosphere is about 9 x 105 volts. Thus the model roughly resembles a parallel-plate capacitor.
For these questions, you may consider the charge on the electron to be –1.6 x 10–19 C.
Assuming the electric potential at the Earth's surfaceis zero, which of the following best represents the electric potential as a function of height h above the Earth's surface?