Question

Answer the following : (a) The top fo the atmosphere is at about 400 kv with respect to the surface of earth, the field is about `100 Vm^(-1)`. Why then do we not get an electric shock, as we step out of out house into the open ? (Assume the house to be a steel cage so that there is no field inside).
(b) A man fixes outside his house one evening a two meter high insulating slab carrying on its top, a large aluminium sheet of area `1 m^(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 conducity of air is known to be 1800 A on an average over the globe. Why then does the atomsphere not discharge itself complety in due course and become electrically neutral ? In other words, what keeps the atmosphere charged ?
(d) What are teh forms of energy into which the electrical energy fo the atmosphere is dissipated during a lighting ?

Answer 1

(a) Since our body and the surface of earth, both are conducting, therefore, our body and the ground form an equipotential surface. As we step out into the open from our house , the orignal equipotential surfaces of open air charge, keeping our body and the ground at the same potential. That is why we donot get an electric shock.
(b) Yes, the man will get the shock. This is because the steady discharging current of the atmostphere charegs up the aluminium sheet gradually adn raises its voltage to an extent depending on the capacitance of the condenser formed by the aluminium sheet, the ground and the insulating slab.
(c) The atomosphere is being charged continously be thunderstoms and lighting all over the globe. It is also discharging due to the small conductivity of air. The two opposing process, on an average,are in equilibrium. Therefore the atmosphere keeps charged.
(d) During a lighting the electrical energy of the atmosphere is dissipated in the form of light heat and sound.