The earth's surface has a negative surface charge density of 10^(-9)C m^(-2). The potential difference of 400 kV between the top of the atmosphere and the surface results (due to the low conductivity of the lower atmosphere) in a current of only 1800 A over the entire globe. If there were no mechanism of sustaining atmospheric electric field, how much time (roughly) would be required to neutralise the earth's surface ? (This never happens in practice because there is a mechanism to replenish electric charges, namely the continual thunderstorms and lightning in different parts of the globe.) (Radius of earth = 6.37xx10^6 m)

The earth's surface has a negative surface charge density of 10^(-9)C

1.	The earth's surface has a negative surface charge density of 10^(-9)C m^(-2). The potential difference of 400 kV between the top of the atmosphere and the surface results (due to the low conductivity of the lower atmosphere) in a current of only 1800 A over the entire globe. If there were no mechanism of sustaining atmospheric electric field, how much time (roughly) would be required to neutralise the earth's surface ? (This never happens in practice because there is a mechanism to replenish electric charges, namely the continual thunderstorms and lightning in different parts of the globe.) (Radius of earth = 6.37xx10^6 m)
Answer» Solution :Using the radius of earth, obtain total charge of the globe. DIVIDE it by current to obtain TIME = 283 s. Still this method GIVES you only an estimate, it is not strictly CORRECT.

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