The earth's surface has a negative surface charge density of $10^{-9}cm^{-2}$. The potential difference of $400\;kv$ between the top of the atmosphere and the surface results (due to low conductivity of the lower atmosphere ) in a current of only $1800\;A$ over the entire globe. If their were no mechanism of sustaining atmosphere field, how much time (roughly) would be required to neutralise the the earth's surface ? (This never happen in practice became there is a mechanism to replenish electric charges namely the continual thunder storms and lighting in different parts of the globe) . Radius of the earth $=6.37 \times 10^6m$

Question

$\begin{array}{1 1} 28.315\;s \\ 283.1\;s \\ 28.31\;min \\ 283.1\;min \end{array}$