Question

The electrical potential of the earth is taken as
A.)Zero
B.)Infinity
C.)Unity
D.)None of these

Answer 1

Hint: The earth’s surface is said to be a pool of infinite negative charges. While the atmosphere of the earth consists mainly of positive ions. So there must be a potential gradient set up between the atmosphere and the surface of the earth. So the charge distribution over the whole of earth is zero.

Complete step by step answer:
The earth’s surface is considered as an infinite pool of negative charges, we can determine this by placing a metal plate slightly above the surface of the earth and grounding it to the ground. After some time, the plate acquires a negative surface charge density, which shows there are negative ions or charges present on the surface of the earth.

So, What about the positive charges in the atmosphere? These positive charges are mainly formed due to the cosmic rays that arrive at earth at each moment. These cosmic rays interact with the molecules in the atmosphere, and ions are produced in the process. These ionization increases as we go from the surface of the earth to the exosphere. So the positive charges will be accumulated more in the higher altitudes as compared with lower altitudes.

Since there is a potential gradient existing between the negative charges on the earth and the positive charges in the atmosphere, a current can flow from the atmosphere to the surface of the earth which neutralises the negative charges on the earth.
So simply we can say that the total amount of charge enclosed by the earth is zero. So the potential associated with the earth is taken as zero.

So the answer to the question is option (A)-zero.

Note:
If the charges are neutralised, how do the infinite negative charges on earth exist or be maintained. This can be attributed to lightning, which brings back negative charges onto the earth’s surface.
Lightning’s are occurring all around the world at the rate of 40,000 thunderstorms per day, and on an average, these thunderstorms contribute over 1800 amperes of negative charge to the earth’s surface, which compensates for the charge neutralisation.