Surface charge density of the earth, σ=10−9 Cm−2
Current over the entire globe, I=1800 A
Radius of the earth, r=6.37×106 m
Surface area of the earth,
A=4πr2=5.09×1014 m2
Charge on earth surface, q=σA=5.09×105 C
Time taken to neutralize the earth’s surface = t.
Current I=qt
⟹t=5.09×105/1800=283 s