a. The top of the atmosphere is at about 400 kV with respectto the surface of the earth, corresponding to an electric field that decreases with altitude. Near the surface of the earth, the field is about `100 Vm^(-1).` Why then do we not get a electric shock as we step out of our house into the openy (Assume the house to be a steel cage so there is no field inside!)
b. A man fixes outside his house one evening a two metre high insulating slab carrying on its top a large aluminium sheet of area `1m^(2)`. Will he get an electric shock if he touches the metal sheet next morning?
c. The discharging current in the atmosphere due to the small conductivity of air is known to be 1800A on an average over the globe. Why then does the atmosphere not discharge itself completely in due course and become electrically neutral? In other words, what keeps the atmosphere charged?
d. What are the forms of energy into which the electrical energy of the atmosphere is dissipated during a lightning? (Hint: The earth has an electric field of about `100 Vm^(-1)` at its surface in the downward direction, corresponding to a surface charge density `=-10^(-9) Cm^(-2) ?.`

Explanation

a. Our body and the ground form an equipotential surface. As we step out into the open, the original equipotential surfaces of open air change, keeping our head and the ground at the same potential.
b. Yes. The steady discharging current in the atmosphere charges up the aluminium sheet gradually and raises its voltage to an extent depending on the capacitance of the capacitor (formed by the sheet, slab and the ground).
c. The atmosphere is continually being charged by thunderstorms and lightning all over the globe and discharged through regions of ordinary weather. The two opposing currents are, on an average, in equilibrium.
d. Light energy involved in lightning, heat and sound energy in the accompanying thunder.